Nitrogen Fixation: Root and Bacteria Interactions
Nitrogen is an important macronutrient because it is part of nucleic acids and proteins. Atmospheric nitrogen, which is the diatomic molecule N2, or dinitrogen, is the largest pool of nitrogen in terrestrial ecosystems. However, nitrogen can be “fixed,” which means that it can be converted to ammonia (NH3) through biological, physical, or chemical processes. As you have learned, biological nitrogen fixation (BNF) is the conversion of atmospheric nitrogen (N2) into ammonia (NH3), exclusively carried out by prokaryotes such as soil bacteria or cyanobacteria. The following equation represents the process:
The most important source of BNF is the symbiotic interaction between soil bacteria and legume plants, including many crops important to humans (Figure 1). The NH3 resulting from fixation can be transported into plant tissue and incorporated into amino acids, which are then made into plant proteins. Some legume seeds, such as soybeans and peanuts, contain high levels of protein, and serve among the most important agricultural sources of protein in the world.
Farmers often rotate corn (a cereal crop) and soy beans (a legume), planting a field with each crop in alternate seasons. What advantage might this crop rotation confer?
[reveal-answer q=”890921″]Show Answer[/reveal-answer]
[hidden-answer a=”890921″]Soybeans are able to fix nitrogen in their roots, which are not harvested at the end of the growing season. The belowground nitrogen can be used in the next season by the corn.[/hidden-answer]
Soil bacteria, collectively called rhizobia, symbiotically interact with legume roots to form specialized structures called nodules, in which nitrogen fixation takes place. This process entails the reduction of atmospheric nitrogen to ammonia, by means of the enzyme nitrogenase. Therefore, using rhizobia is a natural and environmentally friendly way to fertilize plants, as opposed to chemical fertilization that uses a nonrenewable resource, such as natural gas. Through symbiotic nitrogen fixation, the plant benefits from using an endless source of nitrogen from the atmosphere. The process simultaneously contributes to soil fertility because the plant root system leaves behind some of the biologically available nitrogen. As in any symbiosis, both organisms benefit from the interaction: the plant obtains ammonia, and bacteria obtain carbon compounds generated through photosynthesis, as well as a protected niche in which to grow (Figure 2).
Mycorrhizae: The Symbiotic Relationship between Fungi and Roots
A nutrient depletion zone can develop when there is rapid soil solution uptake, low nutrient concentration, low diffusion rate, or low soil moisture. These conditions are very common; therefore, most plants rely on fungi to facilitate the uptake of minerals from the soil. Fungi form symbiotic associations called mycorrhizae with plant roots, in which the fungi actually are integrated into the physical structure of the root. The fungi colonize the living root tissue during active plant growth.
Through mycorrhization, the plant obtains mainly phosphate and other minerals, such as zinc and copper, from the soil. The fungus obtains nutrients, such as sugars, from the plant root (Figure 3). Mycorrhizae help increase the surface area of the plant root system because hyphae, which are narrow, can spread beyond the nutrient depletion zone. Hyphae can grow into small soil pores that allow access to phosphorus that would otherwise be unavailable to the plant. The beneficial effect on the plant is best observed in poor soils. The benefit to fungi is that they can obtain up to 20 percent of the total carbon accessed by plants. Mycorrhizae functions as a physical barrier to pathogens. It also provides an induction of generalized host defense mechanisms, and sometimes involves production of antibiotic compounds by the fungi.
There are two types of mycorrhizae: ectomycorrhizae and endomycorrhizae. Ectomycorrhizae form an extensive dense sheath around the roots, called a mantle. Hyphae from the fungi extend from the mantle into the soil, which increases the surface area for water and mineral absorption. This type of mycorrhizae is found in forest trees, especially conifers, birches, and oaks. Endomycorrhizae, also called arbuscular mycorrhizae, do not form a dense sheath over the root. Instead, the fungal mycelium is embedded within the root tissue. Endomycorrhizae are found in the roots of more than 80 percent of terrestrial plants.
What Is The Difference Between Autotrophic And Heterotrophic Organisms?
We explain that what is the difference between Autotrophic and Heterotrophic Organisms? with the examples of autotrophs and heterotrophs Organisms. In addition: Definitions and energy production in detail to easily understand.
Do you know how the beings that live on Earth nourish themselves and get energy? We know that animals get energy when they eat, but what happens, for example, with algae or other beings that do not have a mouth and a digestive system?
We will see what is the definition of autotrophic and heterotrophic beings , the differences between autotrophic and heterotrophic nutrition and some examples to understand it better. Continue reading the article to learn more about the beings that populate our planet!
Welcome to the Living World
It is the partial oxidation (breakdown) of glucose to 2 molecules of pyruvic acid (C 3 H 4 O 3 ) in the absence of O 2 . It occurs in cytoplasm of all living organisms.
Its scheme was given by Gustav Embden, Otto Meyerhof & J. Parnas. So it is also known as EMP pathway.
In anaerobes, it is the only process in respiration.
In plants, glucose is derived from sucrose (end product of photosynthesis) or from storage carbohydrates. Sucrose is converted to glucose & fructose by an enzyme, invertase.These 2 monosaccharides readily enter glycolytic pathway.
Glucose & fructose are phosphorylated to form glucose-6-phosphate by the enzyme hexokinase. It is then isomerised to produce fructose-6-phosphate. Subsequent steps of metabolism of glucose and fructose are same.
It includes 10 steps under the control of different enzymes.
- In the conversion of glucose into glucose 6-phosphate.
- In the conversion of fructose 6-phosphate to fructose 1, 6-diphosphate.
PGAL is oxidised and with inorganic phosphate get converted to 1, 3-bisphosphoglycerate (BPGA). During this, 2 redox-equivalents (2 H-atoms) are removed from PGAL and transferred to NAD+ forming NADH + H+.
BPGA becomes 3-phosphoglyceric acid (PGA) yielding energy. This energy is trapped by the formation of ATP.
ATP is also formed when PEP converts to pyruvic acid.
In glycolysis, 4 ATP molecules are directly synthesised from one glucose molecule.
Pyruvic acid (pyruvate) is the key product of glycolysis. Its metabolic fate depends on the cellular need.
Part 3: Plant’s Perspective on Seeds, Sex, and Microbes
00:00:13.17 My name is Ian Baldwin and I am delighted to be giving Part 3 of a talk entitled Studying
00:00:20.05 a plant's ecological interactions of the genome. in the genomics era.
00:00:24.20 In Parts 1 and 2, I gave a short, biased history of this very interdisciplinary field of plant-herbivore
00:00:31.12 interactions, and I also talked a lot about the model system that we work with, Nicotiana
00:00:35.14 attenuata, and how it deals with attack from a nicotine-tolerant herbivore.
00:00:40.07 In this talk, I'm going to be telling you about how the plant utilizes, well, sex and
00:00:46.24 microbes to be able to protected its seeds and try. try to present that in an evolutionary
00:00:53.24 We've been working on this plant, Nicotiana attenuata.
00:00:56.19 It grows in the Great Basin Desert of the United States.
00:00:59.09 It's a native plant and thanks to the long-term, patient funding of the Max Planck Society,
00:01:04.02 we've developed a very impressive toolbox, molecular toolbox for this particular plant.
00:01:09.15 And we transform the plant in our laboratories in Germany, and take the plant back out to
00:01:14.04 a field station in Utah to study its ecological interactions.
00:01:19.00 In Part 2, I talked a lot about how the plant deals with attack from this particular specialist
00:01:24.23 herbivore, Manduca sexta, and how the herbivore has particular elements in its oral secretions,
00:01:31.00 its spit, called fatty acid amino acid conjugates.
00:01:34.07 These are the structures, and these FACs are the signals that elicit a six-layer series
00:01:40.12 of responses in the plant that involve defense, avoidance, and tolerance.
00:01:45.12 And these are the ones that I talked about in Part 2 of the talk.
00:01:49.05 I want to start this talk off by building on part six, the ability of the plant to avoid
00:01:57.01 this particular herbivore by changing pollinators.
00:02:00.04 Now, what I told you about last time was that this pollinator, the mother of the larvae,
00:02:07.00 is a good guy because it's an excellent pollinator, but it. every time it pollinates it nectars
00:02:12.00 and lays eggs, and the eggs of course hatch into the bad guy.
00:02:15.19 And the plant has come up with the solution of solving this particular dilemma of having
00:02:19.20 a good guy and a bad guy in the same genome by switching the type of flowers that it produces.
00:02:25.15 So, normally it produces these night-open flowers, as you can see here, and these are
00:02:31.03 pollinated by the moth -- they open up at night and scent at night and attract the moth
00:02:35.17 at night times.
00:02:37.02 But when it's heavily attacked by the larvae of the moth's babies, then the plant begins
00:02:43.24 to produce these morning-open flowers, here, and these morning-open flowers are not pollinated
00:02:50.07 by hawk moths -- it doesn't even attract them because it doesn't scent at night -- but rather
00:02:54.20 opens up in the morning time and is pollinated by hummingbirds.
00:02:59.01 Now, hummingbirds have this wonderful characteristic that they don't lay. they law hummingbird
00:03:03.16 eggs. they don't lay moth eggs, and so it avoids the whole problem of attracting a major
00:03:07.15 herbivore by getting good pollination services.
00:03:10.24 Now, you might be asking, why doesn't the plant always make those morning-open flowers
00:03:16.14 instead of those night-open flowers and just go with the hummingbird instead?
00:03:20.11 Well, we think the reason is because the hummingbird is not a very good outcrosser.
00:03:26.12 It likes to trap-line -- it moves from flower to flower to flower in the plant and therefore
00:03:30.08 largely selfing the plant.
00:03:32.03 And if you go out and look at a seed capsule in a natural population like this one and
00:03:37.07 you sequence the seeds that are in that seed capsule, you'll find that there's an awful
00:03:41.04 lot of outcrossed seeds, which means that, despite the fact that this is a selfing plant,
00:03:47.01 that this is a plant that is perfectly capable of selfing, it shows no evidence of inbreeding
00:03:52.13 depression, but in the natural world it does a lot of outcrossing.
00:03:56.23 Now, why is that crossing so important to this particular plant?
00:04:00.05 Well, it's probably a consequence of the fact that it chases fires in ecologic time, as
00:04:06.04 I told you about in Part 1 of this talk.
00:04:08.20 And it chases fires by producing a seed that lives in the seed bank for a long period of
00:04:13.24 time, in that inter-fire interval.
00:04:16.05 Now, if you're going to survive in the seed bank for a long period of time, it's much
00:04:20.19 better to have many different copies of a lottery ticket, to hope that you're going
00:04:26.14 to find that one particular geno. genotypic combination which allows you to survive all
00:04:32.00 the different things that might happen in the hundreds of years while you lie dormant,
00:04:35.16 as compared to having many copies of the same seed, many copies of the same lottery ticket,
00:04:41.11 which is what happens when you self.
00:04:42.23 So, we think that outcrossing is very important because it provides the genetic material,
00:04:48.10 the genetic diversity, that allows you to survive this long inter-fire interval.
00:04:53.12 So, in this talk, what I'm going to do is tell you about three elements that might help
00:04:59.15 this plant survive that long-term inter-fire interval, and be able to still evolve quickly,
00:05:06.12 despite this very long component of its life stage.
00:05:09.08 I'm going to talk about pollinator attraction, I'm going to talk about post-pollination mate
00:05:13.09 selection, I'm going to talk about opportunity. opportunistic mutualisms that the plant develops
00:05:20.08 with microbes that are in the soil.
00:05:23.00 And I'm going to first start out with the pollinator attraction.
00:05:25.07 But, to do that, I need to set a context of mate selection for plants.
00:05:30.06 Now, plants can select mates at two different stages, actually at 3 different stages that
00:05:36.00 I'm going to tell you about, but I'm just gonna describe experimental evidence. evidence
00:05:39.15 for two of them.
00:05:40.22 The first stage can be the pre-pollination stage, when it brings in different pollinators
00:05:46.11 that will then bring in pollen loads that have different types of genetic. different
00:05:51.04 genetic compositions.
00:05:52.20 And I'll talk a little about the flower traits that select for particular types of pollinators.
00:05:58.04 Then, there's a stage of the post-pollination pre-zygotic selection, and that is when the
00:06:05.09 gamete delivery device, which is first. it really contains. composed of two parts.
00:06:11.09 Its first part is the postman that brings the pollen grains to the stigma, and then
00:06:16.15 the second part of the gamete delivery device is the pollen tubes that actually grow through
00:06:21.00 the style, and then deliver the two sperm nuclei that conduct the double fertilization
00:06:27.05 that isn't required for seed development, the fertilization of the embryo and the fertilization
00:06:32.18 of the endosperm.
00:06:34.09 And then, lastly, the third arena of mate selection, which I'm not going to talk about
00:06:39.00 in this, but I just wanted to mention, is the post-zygotic mate selection that involves
00:06:43.08 differential seed filling and seed abortion, once the seeds have been fertilized -- post-zygotic
00:06:49.13 mate selection.
00:06:51.22 So, in order to out. to maximize outcrossing, so that you have some opportunity to select
00:06:57.16 mates, you've got to get pollinators who have visited a number of different plants of different
00:07:03.08 genotypes, be attracted to a flower, and deposit those pollen grains onto the stigma.
00:07:08.08 Now, we've been looking at many of the different pollinators that visit attenuata flowers and
00:07:13.07 we're trying to find out whether or not some of them deliver different qualities of genetic
00:07:19.01 material to the flower.
00:07:21.02 And what I want to do is talk a little bit about how it is that particular pollinators
00:07:25.04 are manipulated by floral traits, so that they can be enhanced and selected for by the
00:07:31.18 Now, I mentioned that the hummingbird, there depicted, is probably not as good of a pollinator
00:07:37.17 as the moth, simply because of its behavior of trap-lining and largely selfing the plants.
00:07:44.17 But I want to tell you a little trick that the plant conducts to be able to get better
00:07:49.08 outcrossing services from this particular hummingbird.
00:07:52.02 And here we have to look at the chemistry of both the headspace of the flower as well
00:07:56.17 as the nectar.
00:07:57.22 And if you look carefully at the chemistry of the headspace, you see there's lots of
00:08:00.24 different molecules there -- there's peaks on the chromatogram that are numbered -- and
00:08:04.08 you'll notice that benzylacetone, the molecule I told you about in Part 1 of this talk, as
00:08:08.22 well as Part 2 of this talk, is the main floral attractant.
00:08:13.19 But there's another peak that comes right after benzylacetone and that's a surprising
00:08:17.15 peak because it's a poison.
00:08:19.08 It's the nicotine molecule I told you about in Part 2.
00:08:22.07 And you can see that the nicotine peak is quite large in the nectar, in particular.
00:08:27.13 And that asks a very interesting question: why would you want to put a poison in the
00:08:33.01 very nectar, the very reward, that you're trying to use to attract pollinators with?
00:08:39.10 So, the first question we had was, well, maybe nicotine isn't a repellent for hummingbirds
00:08:44.23 and maybe even nicotine allows hummingbirds to become addicted to these flowers?
00:08:49.09 And in a number of experiments that Danny Kessler and I did with some extremely high-tech,
00:08:53.20 Max Planck-level equipment that involved oil drums and Easter Lily flowers, we were able
00:09:00.05 to show very nicely that, within the concentration range of nicotine in the nectar, it's very
00:09:06.22 clear that nicotine is a repellent to hummingbirds and we were also able to demonstrate that
00:09:12.09 hummingbirds do not become addicted to nicotine, unlike human beings.
00:09:18.04 And if you look at the concentrations of nicotine in the nectar of plants from 10 different
00:09:25.00 populations, and here you're seeing data from five plants from ten populations, with the
00:09:29.23 mean and standard error of six flowers from each one of those five plants from the ten
00:09:35.18 different populations, you see that the concentrations vary all over the place, but there's a large
00:09:41.10 fraction of the flowers that are producing concentrations that are repellent to the hummingbirds
00:09:47.03 and some of them are even producing concentrations that are quite toxic.
00:09:51.00 And if you look closer, within a given and inflorescence, you find the explanation for
00:09:55.09 why the standard error bars on that graph are so large.
00:09:59.18 And the reason is that the flowers within the inflorescence have a random distribution
00:10:04.20 of nicotine in their nectar.
00:10:07.06 There is one really poisonous flower, usually, in a typical inflorescence, while the other
00:10:12.18 ones are not so bad at all, and there's no predictability for where that particular poisonous
00:10:18.18 flower is.
00:10:20.02 And this affects hummingbird behavior in a very characteristic way, because they tell
00:10:24.18 you very nicely when they don't like a nectar -- they basically probe and then they back
00:10:30.12 off and spit and they they fly away.
00:10:33.00 And here comes a hummingbird flying along, trap-lining, hitting a poisoned flower, there,
00:10:37.11 and then popping off to another plant.
00:10:39.03 And we hypothesized, by having a randomly poisoned flower in an inflorescence, the plant
00:10:45.10 is able to get better outcrossing rates from these relatively poor outcrossing hummingbird
00:10:52.18 So, we conduct an experiment.
00:10:53.18 The experiment was very simple.
00:10:54.18 We simply just transformed the plants so that we could silence nicotine production and we
00:10:59.02 antherectomized flowers so that flowers would only receive pollen if they were visited by
00:11:05.11 a hummingbird, and to ensure that we covered up the plants at night, and had them only
00:11:09.20 exposed during the daytime -- we did that in two native populations -- and then we genotyped
00:11:15.09 all the seeds produced from those flowers that were pollinated by and fertilized by
00:11:19.12 those hummingbirds.
00:11:20.22 And. and the results are very clear.
00:11:23.12 For. for plants, for flowers that were producing nicotine and had that random poisonous flower
00:11:29.04 in the bouquet, they had significantly more fathers fathering their seeds than the flowers
00:11:36.06 that did not produce nicotine.
00:11:38.08 So, nicotine-laced nectar increases outcrossing rates.
00:11:41.15 So, I think it's abundantly clear that we shouldn't be thinking of nectar as simply
00:11:46.11 just the solution of sucrose and glucose and fructose that is a reward for. to pay the
00:11:53.01 postman with.
00:11:54.15 We should consider all the other metabolites that frequently occur in nectar solutions
00:11:58.17 and think about them in the context. very much similar to the context of the secret
00:12:03.08 formulas of many of the soft drink producers, namely, to manipulate how the consumer behaves,
00:12:08.24 and the plant is of course using chemistry to be able to optimize outcrossing and solve
00:12:14.20 all the other problems that pollination entails.
00:12:17.17 Now, in addition to using chemistry, a plant also uses its morphology, its movement.
00:12:23.18 And here you see a time-lapse video of a flower that undergoes a movement behavior of starting
00:12:31.00 out low during the early evening, and then slowly up, increasing its angle, opening up
00:12:38.02 its corolla, scenting, going through anthesis, and then getting ready to receive its favorite
00:12:46.17 And this movement turns out to be circadian it happens on a daily basis for the three
00:12:51.12 days that a flower is open.
00:12:53.14 It turns out to be controlled by the plant's clock -- there's a little clock in the pedicel
00:12:57.19 of the flower that controls that movement behavior.
00:13:00.18 I'm not going to talk about that now, but I do want to address the question about why
00:13:04.19 these flowers wave, why they do this waving behavior.
00:13:07.23 Now, again, using very technical Max Planck-level type of equipment, Danny Kessler and Felipe
00:13:14.07 Yon had taken soda straws that they got from McDonald's and use them to tether the flowers
00:13:22.10 in particular positions -- up high like a flower would be at night, at the horizontal
00:13:27.20 as it would be in the afternoon, and then downward as it would be in midday -- and then
00:13:31.11 simply allowed a hawk moth to pollinate and interact with these flowers that had all been
00:13:37.19 antherectomized -- an incision was made to take out the pollen grains.
00:13:41.05 And, as you can see, if the flowers are in their upward position, the hawk moth is able
00:13:46.09 to pollinate and access the flowers, and the flower would be able to mature seeds and capsules
00:13:52.14 as it would normally would.
00:13:53.21 Now, I told you in Part 1 that the hawk moth uses this sensory sensilla on the end of that
00:13:59.14 very long proboscis you can see right here to find its way into the flower using the
00:14:06.03 floral scent that not only acts as a long-distance attraction. attractant, but also a very
00:14:11.22 short-distance cue that allows the moth to find the hole of the flower.
00:14:15.10 Now I'm telling you that there's an additional layer to this interaction, that the flower
00:14:20.16 basically has to get it up so the moth can get it in -- it's very much like Dirty Dancing.
00:14:26.22 The flower is using this moving behavior to filter out other pollinators so that it's
00:14:32.08 pollinated primarily by its favored one, this Manduca sexta.
00:14:37.13 So, there are clearly many other ways in which plants could be. flowers could be manipulating
00:14:42.19 and choosing particular type of pollinators and pollinators may be delivering different
00:14:47.23 pollen loads of different genetic quality, but we simply don't know very much about that.
00:14:52.05 Now, I want to switch to the next stage in the potential for mate selection in flowers,
00:14:56.18 and that is the post-pollination, pre-zygotic possibilities, and tell you about the role
00:15:02.16 that ethylene, a plant phytohormone, that it plays in this process.
00:15:08.05 And I'm gonna start out with two plants that we have sequenced, that occur on the opposite
00:15:14.09 sides of the Grand Canyon: one to the north of the Grand Canyon, we call the Utah Lady
00:15:19.22 and one to the south of the Grand Canyon, that we call the Arizona Lady.
00:15:23.12 Both of their genomes would have been released just recently.
00:15:28.02 And we've basically asked these two ladies to tell us what they think about various men
00:15:33.22 from both Utah and Arizona.
00:15:35.07 And I'm going to only give you the data, today, on the mate preferences from the Utah men
00:15:43.09 from these two particular ladies.
00:15:44.24 Now, when these two particular ladies were asked, in mixed pollen pollination experiments,
00:15:51.01 where all men had equal numbers of pollen grains placed on the stigma, to choose, and
00:15:56.24 you can see that the lady from Utah made a very particular choice and clearly had Mr.
00:16:05.04 G2 from Utah as its favorite, and did not like G10 at all, while the lady from Arizona
00:16:10.19 liked G10 and didn't have any preference, and didn't sire any seeds with G2.
00:16:17.04 And these preferences for G2 and G10, respectively, between the two ladies, were consistent across
00:16:22.23 years from 2008 through 2010, and a number of different replicates in 2010 with many
00:16:28.21 different filial generations of the men.
00:16:31.20 And you can see these are very consistent mate choices on the part of these two flowers.
00:16:38.09 two flower types.
00:16:40.06 Now, what's interesting about these particular choices, if we just go back to the lady from
00:16:43.23 Utah, who likes G2, if she gets G2 placed on her stigma, she shuts down the advertisement
00:16:51.16 -- she no longer scents, produces this benzylacetone scent to attract pollinators, and she goes
00:16:56.21 ahead and sires a large number of her seeds, 28% of them, with the G2 pollen source.
00:17:03.04 If, on the other hand, she receives primarily the unfavored G10 pollen source, she continues
00:17:09.12 to advertise -- she continues to emit floral scents, perhaps hoping to be able to bring
00:17:13.13 in one of her favorite pollen grains.
00:17:16.16 Now, you may be wondering, since we've been doing these experiments with antherectomized
00:17:19.19 flowers that don't have all that self. potential for self-pollination, you wonder whether or
00:17:24.14 not being same mate preferences might occur with a lot of self pollen, and indeed they
00:17:29.21 If you don't antherectomize them, you of course get a large number of self-pollinated seeds
00:17:33.19 -- so, self-pollination is sort of a backup, a security blanket -- but they still show
00:17:37.11 those very distinct preferences for G2, if you're the Utah lady.
00:17:42.01 Now, you may also be thinking that, well, maybe these men just are. some of them are
00:17:47.01 wimps and are not really very good at siring seeds.
00:17:50.08 So, we did a bunch of experiments with single genotype pollination, giving each one of the
00:17:54.24 26 men an opportunity to pollinate seeds in both of the genetic backgrounds, and turns
00:17:59.13 out that all of them are perfectly viable men.
00:18:02.24 They're perfectly capable of producing pollen tubes and fertilized seeds that are perfectly
00:18:06.24 valuable and fecund.
00:18:08.16 So, there's nothing wrong with the men.
00:18:10.21 It's really a question of the females choosing.
00:18:13.09 Now, there's another component of this process that I need to tell you about.
00:18:18.05 When a mixed pollen load comes and there is one of the favored pollen grains in that mixed
00:18:23.07 problem load, the plant responds very rapidly after the pollen is deposited on the stigma
00:18:28.13 with a little ethylene burst, this phytohormone.
00:18:32.03 And the ethylene burst is directly proportional to the preference of the female for the mates
00:18:38.18 that have been deposited on the pollen.
00:18:40.14 So, the ethylene burst is a harbinger of future mate preferences, once the pollen tubes are
00:18:46.09 grown down and fertilization occurs.
00:18:48.18 Now, we have the ability, genetically, to abrogate the ethylene signaling process.
00:18:53.02 We can do it in two ways: we can make plants that are ethylene mute, because they can't
00:18:56.16 speak ethylene, they can't produce ethylene -- so we do that by knocking out a gene called
00:19:00.19 ACC oxidase -- and we can also make plants ethylene deaf, that can't hear ethylene, because
00:19:06.16 we've been able to abrogate the perception, the receptor that ethylene is perceived by
00:19:11.12 in plants, by expressing an ETR1.
00:19:15.00 And in these two plants that are genetically unable to either produce or perceive ethylene,
00:19:20.19 the ethylene burst is abrogated, the plants continue, even when they're pollinated, to
00:19:26.02 produce the floral scent, they advertise and advertise, and what's most interesting is
00:19:30.12 that every single pollen grain deposited on the stigma grows a pollen tube, and successfully
00:19:36.09 fertilizers seeds in direct proportion to the number of pollen grains placed on the
00:19:41.03 So, that again tells you that there's nothing wrong with these men it's all a process of
00:19:45.23 pre-zygotic mate choice happening in this. in the stylar tissues.
00:19:51.07 And you can show that very nicely by taking all the men that we'd had from Arizona, Utah,
00:19:55.21 making one big mixed pollination with equal numbers of pollen grains and pollinating the
00:20:00.07 ethylene deaf plants, and you can see that the number of seeds produced here really reflect
00:20:04.17 pretty much the distribution of pollen grains on the stigma, again.
00:20:09.00 So now, for the really big question, is. these females have very specific and consistent
00:20:16.16 mate choice preferences. are these preferences adaptive?
00:20:20.10 In other words, can the female actually select good mates versus bad mates?
00:20:25.07 Now, how do you do that?
00:20:27.06 Well, one way to do that is to find out whether or not the mates that they choose sire seeds
00:20:33.15 that live longer in the seed bank and are able to grow into viable offspring when the
00:20:38.12 seed bank finally gets activated.
00:20:39.23 So, we've been testing that hypothesis over the last almost 15 years, creating seed bags.
00:20:45.21 seed banks all over Utah with various combinations of seeds, and testing and looking at all the
00:20:51.15 different mortality agents of the seeds, because the seeds are attacked by fungi and other
00:20:55.09 types of bacteria as they lie there in the seed bank.
00:20:58.11 And. and this process is one where we wanted to see whether or not the preferences that
00:21:05.07 the females were making were also producing offspring that lived longer in the seed bank.
00:21:12.06 So, remember the lady from Utah?
00:21:14.12 She likes, when she's given a choice amongst these 11 men from Utah, she likes G2.
00:21:21.11 And it turns out that G2, when you bury those seeds in the seed banks, they survive much
00:21:26.11 better than the other ones -- hey survive better in mixed pollinations they survive
00:21:30.02 better in single pollinations.
00:21:31.22 And remember that lady from Arizona?
00:21:33.08 She liked G10.
00:21:34.20 And G10 survives much better in at least two of the. two of the burial sites much better
00:21:40.08 in single and as well as a mixed pollinations.
00:21:42.16 So, it's pretty clear that the selected mates survive better in those seed banks, and we
00:21:48.05 can infer from that that this mate choice is adaptive.
00:21:52.05 Now, we don't really have any idea how the females are able to make these adaptive mate
00:21:57.19 choices amongst the men.
00:21:59.08 But we want to maybe think a little bit about what happens in animal systems.
00:22:03.00 In animals, the gamete delivery system that we call males is a diploid, and sometimes
00:22:10.19 these diploids end up being selected by females to have very particular types of behavior.
00:22:16.13 They have certain exaggerated traits like you've seen in the pictures in the background.
00:22:21.03 Sometimes they have exaggerated fighting behaviors, where they display their strength and virility,
00:22:25.21 and then females. and then they're supposed to be watching these behaviors and making.
00:22:29.10 saying, well, maybe I can infer that the genetic quality of a particular mate that is dominant
00:22:35.19 in these. in these behaviors it's a good person to be. a good mate to be mating with.
00:22:42.07 And Darwin recognized this as sexual selection in a very important paper in 19. in 1871.
00:22:49.21 And he inferred from the basic principles of how we define male and female that sexual
00:22:58.06 selection should be a very important evolutionary process, simply because we defined females
00:23:04.01 as being the ones that make the big, expensive, and few gametes, and we define males as the
00:23:09.02 one that makes the many, small, inexpensive gametes, that there's going to be male-male
00:23:12.24 competition and female choice, and that there's going to be selection on males and females
00:23:19.02 by the other sex.
00:23:20.18 Now, let's think about mate choice in plants.
00:23:24.15 And there are basically two parts to the gamete delivery system.
00:23:28.08 There's part one when the pollinator brings the mixed load into it, and we've just talked
00:23:32.07 about how different floral traits could maybe select for different types of pollinators
00:23:36.06 they may be bringing different quality mates to the stigma.
00:23:43.07 But then there's part two, which I think is much more interesting.
00:23:47.15 Part two is when the pollen tubes grow down and deliver the two sperm nuclei for the double
00:23:53.02 fertilization that occurs in the most angiosperm reproductive systems: the fertilization of
00:24:00.00 the embryo and the fertilization of the endosperm to finally form the seed.
00:24:05.00 Now, that pollen tube that delivers those two sperm nuclei is haploid, unlike the diploid
00:24:12.03 mate. gamete delivery system that we call males in animals.
00:24:17.05 It's haploid and that haploid pollen tube is stripped of all its epigenetic modifications
00:24:23.11 and expresses over 90% of the transcriptome of the genome of a potential mate before fertilization.
00:24:32.23 And this means that a female plant has the ability to get an unvarnished analysis of
00:24:41.05 the heritable genetic quality of a mate before committing to a fertilization.
00:24:46.17 And this contrasts with what a female animal has to do, who has to make a decision based
00:24:51.21 on the behavior and phenotype of a diploid.
00:24:53.18 And we all know that diploids are liars because they can hide recessive alleles by their diploid
00:25:00.15 And this it means that pre-zygotic mate choice in a plant could make mate choice in animals
00:25:06.06 look like a blind date.
00:25:07.24 Now, let's think about, what are the traits that females may be selecting on when they're
00:25:14.09 making this pre-zygotic mate selection?
00:25:17.00 Now, we know that these seeds live in the seed bank for a long period of time, we know
00:25:21.02 that they sit there and wait and they have a circadian clock that tells them to wake
00:25:25.02 up, and listen for, and smell particular cues, and then decide whether or not they're going
00:25:28.08 to either stay dormant or grow again.
00:25:30.24 They're going to stay dormant if there is an unburned vegetation above them that's leaking
00:25:34.15 a bunch of chemicals, particularly terpenoids and abscisic acid.
00:25:38.09 That activates abscisic acid signaling in the seed and it prevents the seeds from germinating
00:25:42.18 -- it keeps them nice and dormant, quiet they're still in that Sleeping Beauty stage.
00:25:46.11 But, if a fire comes along, pyrolyzes all those molecules, creates a bunch of signals
00:25:51.03 that are carotenoids plus some phenolics that stimulate gibberellin signaling, and cause
00:25:56.05 to then. the seeds to then germinate.
00:25:59.13 Now, we wanted to see, what all the traits were that were correlated with those mate
00:26:05.21 And one of the traits that came out in this analysis is that there's a protease inhibitor
00:26:09.09 that I talked about in Part 2 of this series, which is strongly selected for.
00:26:15.15 And the lady from Utah turns out to produce lots of this protease inhibitor and the lady
00:26:19.19 from Arizona turns out to have a nonsense-mediated decay, where this prote. protease inhibitor
00:26:25.11 transcript is degraded and the concentrations are pretty low in seedlings.
00:26:30.01 It's an important defense trait for established seedlings and plants, but we don't really
00:26:35.08 know what this protease inhibitor is doing in the. umm. seed as it lives through
00:26:40.14 the seed bank.
00:26:43.03 What we do know is that if we take. we manipulate protease inhibit production, either from just
00:26:48.12 the natural nonsense-mediated decay of the Utah and Arizona, or by transforming plants.
00:26:54.16 so, we take the Arizona nonsense-mediated decay gene and we remove that from the Arizona
00:26:59.22 plant and replace it with the Utah gene, which works, and we do the opposite, where we silence
00:27:04.18 the Utah gene in the genotype, we get also high and low protease-inhibitor-producing
00:27:09.20 plants, and we take seeds from those, as well as the mate-selected ones, and we bury them
00:27:13.24 in four different places in Utah, and we see that every single time the plants that are
00:27:19.12 producing high levels of protease inhibitor survive better in the seed bank than the ones
00:27:23.18 that are producing low levels of protease inhibitor.
00:27:25.16 Now, we don't really know what this produce inhibitor is doing.
00:27:28.21 And it's probably a complicated process, and it probably also involves another component,
00:27:34.03 which is the third component of this talk, which is the business of acquiring microbiomes.
00:27:39.20 We know that Nicotiana attenuata seeds, when they're created, they're born, they're born
00:27:44.21 They have no microbiome.
00:27:46.18 But as soon as they germinate and they stick their hypocotyl out into the soil, they start
00:27:51.16 to acquire, from that amazing marketplace of different types of microbes that live in
00:27:57.19 the soils of native places in Utah, they acquire particular individual microbes that they carry
00:28:05.05 with them, they harbor, they feed, they cultivate, and they carry them right on through to the
00:28:09.15 end of their lives.
00:28:10.23 And we know that this is a very robust microbiome.
00:28:13.13 It's a microbiome that's robust to geographic variation, it's robust of mycorrhizal associations,
00:28:19.06 so that that the business of whether or not they're. they're establishing mutualisms
00:28:23.09 with mycorrhizal fungi are not something we've been able to test by using mycorrhizal knockout
00:28:28.04 lines, that you can see in this particular reference listed at the bottom.
00:28:32.09 That doesn't influence the composition of the microbiome.
00:28:35.09 And it's also robust to the defense signaling pathway that I talked about in some detail
00:28:41.12 in Part 2 of this talk, namely the jasmonate defense signaling pathway that's so important
00:28:46.10 for protecting plants against herbivores.
00:28:48.15 If you have defenseless plants, they still have the same microbiome, basically, the same
00:28:52.22 core microbiome in the plants.
00:28:55.03 Now, what is interesting is that there is one phytohormone signaling pathway which dramatically
00:29:01.03 influences the microbiome.
00:29:02.18 And that is the ethylene signaling pathway.
00:29:05.02 And if you take the same two ethylene-abrogated plants that I told you about earlier -- the
00:29:10.16 ethylene deaf plants and ethylene mute plants -- and you do inoculation experiments one
00:29:15.14 at a time with the different natural bacterial species that they acquire, they allow anyone
00:29:21.00 to come in.
00:29:22.00 So, in other words, ethylene signaling basically controls the plants immigration policy for
00:29:27.16 the bacterial microbiome that it. that entails.
00:29:33.11 Now, we know that these bacteria can function in important ways for plant fitness as single
00:29:40.15 We know that there's certain bacteria like this Bacillus megaterium that we call V55
00:29:44.10 that plays a very important role in reducing sulfur for the plant when they're sulfur-deficient,
00:29:48.16 and supplying that reduced sulfur in terms of a volatile compound called DMDS that supplies
00:29:54.07 sulfur deficiencies, particularly when the plant is sulfur-deficient because of an overactive
00:29:59.24 Yang cycle, which produces ethylene.
00:30:02.20 And you can read about in those references down there.
00:30:05.03 But plants in the real world don't acquire just one bacterial species they acquire consortia
00:30:12.01 of bacterial species.
00:30:13.13 And we've learned very recently that these consortia of bacteria play a very important
00:30:18.11 role in protecting plants against fungal diseases.
00:30:21.22 The plant, there, on the right, is a plant that does not have its microbiome and is attacked
00:30:26.20 by a native fungal disease of Alternaria and Fusaria, while the one on the left has its
00:30:31.07 native bacterial microbiome and is protected.
00:30:34.17 And what we learned about this process, primarily through an accident. because for almost
00:30:39.11 15 years of planting transgenic plants in Utah, in order to meet APHIS regulations,
00:30:44.13 we have been taking plants that were basically sterile from Germany and planting them into
00:30:49.24 the field site in Utah.
00:30:51.08 And our planting procedure means that the plants were not able to acquire their natural
00:30:56.06 microbiome from the soil until day 33, which is a very long time to be not able to get
00:31:04.02 that very important set of mutualists to you.
00:31:06.12 It's very much like babies who are cesarean-born rather than being vaginally delivered.
00:31:11.21 Cesarean-born babies take a much longer time to acquire their intestinal microbiome that's
00:31:16.12 so important for their immunocompetence.
00:31:19.05 And we were just basically, by planting the plants as sterile out into the field at day
00:31:23.10 33, putting them in a very vulnerable position, which caused them to suffer from this black
00:31:27.09 death disease, and we have a paper in the Proceedings just last year -- Proceedings
00:31:31.09 of the National Academy -- that shows just how effective five bacteria. five native
00:31:37.04 bacteria. and if we just inoculate them at the seedling stage, they're able to protect
00:31:41.13 the plants much more effectively than fungicides and all sorts of cultivation techniques that
00:31:46.14 we've tried that you can read about in that paper if you care about it.
00:31:49.20 Now, we're just beginning to learn about where this microbiome exists and Rakesh Santhanam,
00:31:55.01 who is the genome-enabled field biologist number 52 from the department, who just defended
00:32:01.20 his thesis, has developed some beautiful techniques to visualize these particular microbiomes
00:32:07.03 and, using FISH hybridization techniques, can image exactly where a particular taxa
00:32:13.03 of bacteria is existing on the root surface.
00:32:15.23 And what. what those images are telling us is that they're growing on the root surface
00:32:19.20 and interlacing and interconnecting in sort of diffuse manners and seem to be fed. you
00:32:24.19 can see these little spots of red or green or blue that are particular taxa of bacteria
00:32:29.22 that are growing at a very particular location. and it looks like they're being fed by complex
00:32:34.12 carbohydrates exuded from the root.
00:32:36.10 So, again, going back to the baby analogy, babies, when they drink mother's breast milk,
00:32:42.14 are very much enhanced in their microbiome, because the breast milk contains very complex
00:32:49.11 carbohydrates that only the beneficial bacteria that are good for the baby's immune system
00:32:53.21 can grow on.
00:32:55.00 That's why breast milk is so good for babies.
00:32:57.12 And we think that, perhaps, roots are doing the same thing -- they're producing complex
00:33:01.03 carbohydrates that are encouraging certain bacterial taxa and not others.
00:33:07.02 This is definitely for the future to go at.
00:33:09.02 So, the take-home message here is that, while it's great to have a genome of this plant,
00:33:15.11 and it's wonderful to be able to see how the various sorts of traits that we've learned
00:33:19.05 are important for the natural history of this plant are embedded in that genome, we can
00:33:23.07 see the signatures of it, it's also clear that we're going to have to be taking much
00:33:27.22 more attention to the attenuata's extended genome, namely that of the microbes that it
00:33:33.24 develops mutualistic associations with that are opportunistic with every time they germinate
00:33:38.15 in the soil.
00:33:40.02 And it should also be clear from what I've told you that there is another way that a
00:33:45.20 plant can solve some of its adaptation constraints.
00:33:49.23 For everybody who grew up learning about evolutionary biology from the new synthesis, we had this
00:33:55.05 particular metaphor of constraints on adaptive fitness for a plant.
00:34:01.15 These are fitness landscapes, where fitness is on the y axis and different combinations
00:34:06.07 of nuclear genes are on the x and z axes, and you can see that there's some particular
00:34:11.02 peaks in those fitness landscapes that selection would drive organisms up to the top of these
00:34:16.10 peaks, but then not be able to traverse those crevasses to other peaks, as a consequence
00:34:21.08 of the genetic constraints in the organism's genome.
00:34:24.23 Well, what I've told you about are two ways in which there may be solutions for organisms
00:34:30.20 to be able to traverse these crevasses.
00:34:33.13 One of them is by adopting a mutualistic association to solve a particular fitness problem, like
00:34:40.02 acquiring a microbiome which allows you to then, you know, become much more resistant
00:34:44.21 to fungi or solve your sulfate reduction problems.
00:34:47.19 And also, if you grow in a genetically diverse population, which is exactly what attenuata
00:34:52.10 does, by. through rapid haploid selection during the mating process, you might be able
00:34:58.02 to acquire their alleles, that allow you to then traverse those crevasses in the adaptive
00:35:04.14 So, I think there's much to be learned about how an organism that might have a very long
00:35:10.23 life cycle, because of a long dormancy period, is still able to evolve very rapidly, select
00:35:17.11 for alleles that might optimize its fitness, and select for microbiomes that allow it to
00:35:22.01 short-circuit some of the genetic constraints.
00:35:23.21 So, when you have a plant that grows in populations that are very, very genetically diverse, because
00:35:30.00 when fires swing through they recruit seed banks that are not only last year's seeds,
00:35:35.16 but also seeds from 10 years ago and 100 years ago, you have a lot of diversity there, and
00:35:40.23 if you can select that out, the best alleles out of those very diverse populations, through
00:35:45.22 the mating process, you may be able to optimize your fitness for the long haul.
00:35:52.15 And another point I wanted to make is that I've told you that ethylene signaling plays
00:35:56.17 an important role for harmonizing a plant's phenotype with the environment -- that's something
00:36:00.16 lots of people know.
00:36:01.17 I've also told you that ethylene signaling plays an important role in recruiting the
00:36:05.04 microbiome that's important for the opprotu. for the opportunistic mutualisms.
00:36:09.02 And, also, ethylene signaling plays an important role in the mate selection process.
00:36:13.12 So, a lot of our laboratory's future research will be to understand the role that ethylene
00:36:19.13 signaling plays in this rapid adaptation process.
00:36:23.22 So, I've now come to the end of Part 3 and I hope that the main take-home message of
00:36:31.22 these. these three-part talks is how wonderful it is to be a biologist in this particular
00:36:38.17 time, how wonderful it is to be a genome-enabled field biologist.
00:36:42.13 That allows you to utilize all the amazing molecular and chemical techniques that we
00:36:50.04 can use to manipulate phenotypes at a time when we still have some interesting natural
00:36:55.09 history left on the planet to explore.
00:36:58.16 Thank you for your attention.
00:36:59.20 And I also want to thank all the people who of course fund this work, Brigham Young University
00:37:04.17 particularly for the use of their nature preserve, where we do the releases, for all the many
00:37:09.22 talented photographers who have provided photographs for these talks, and particularly
00:37:14.12 Gundega Lapina, who has done an enormous help in supporting the production of this. of these talks.
00:37:20.09 And for all the scientists in the group who have provided some unpublished data that I've
00:37:24.11 talked about.
00:37:25.11 Thank you for your attention.
- Part 1: A Short Biased History of an Interdisciplinary Field
Figure 3. A Venus flytrap has specialized leaves to trap insects. (credit: “Selena N. B. H.”/Flickr)
An insectivorous plant has specialized leaves to attract and digest insects. The Venus flytrap is popularly known for its insectivorous mode of nutrition, and has leaves that work as traps (Figure 3).
The minerals it obtains from prey compensate for those lacking in the boggy (low pH) soil of its native North Carolina coastal plains. There are three sensitive hairs in the center of each half of each leaf. The edges of each leaf are covered with long spines. Nectar secreted by the plant attracts flies to the leaf. When a fly touches the sensory hairs, the leaf immediately closes. Next, fluids and enzymes break down the prey and minerals are absorbed by the leaf. Since this plant is popular in the horticultural trade, it is threatened in its original habitat.
11.15: Autotrophic Plants - Biology
Plants obtain food in two different ways. Autotrophic plants can make their own food from inorganic raw materials, such as carbon dioxide and water, through photosynthesis in the presence of sunlight. Green plants are included in this group. Some plants, however, are heterotrophic: they are totally parasitic and lacking in chlorophyll. These plants, referred to as holo-parasitic plants, are unable to synthesize organic carbon and draw all of their nutrients from the host plant.
Plants may also enlist the help of microbial partners in nutrient acquisition. Particular species of bacteria and fungi have evolved along with certain plants to create a mutualistic symbiotic relationship with roots. This improves the nutrition of both the plant and the microbe. The formation of nodules in legume plants and mycorrhization can be considered among the nutritional adaptations of plants. However, these are not the only type of adaptations that we may find many plants have other adaptations that allow them to thrive under specific conditions.
Next we have the tiny organisms called bacteria. Like plants and algae, autotrophic bacteria can also gain energy from their surroundings. Let’s examine three tiny bacteria autotrophs.
[caption align=“aligncenter” width=“600”] Cyanobacteria[/caption]
Cyanobacteria Probably one of the most important types of bacteria, cyanobacteria are known to be aquatic and live in large colonies. Cyanobacteria contribute a lot to our planet. For example, Earth’s oxygen is mainly composed from vast amounts of cyanobacteria. Even more interesting is that cyanobacteria also contributes to the development of plants. The chloroplast in plants are actually individual cyanobacterium that are living in a plant’s cell. Without cyanobacteria it’s doubtful we would be able to survive! Green and Purple Sulfur Bacteria Next we have green and purple sulfur bacteria. Green sulfur is often a light greenish color, while purple sulfur is purple or reddish brown. The interesting thing about these two bacteria is that instead of using water to help make their own food, they instead use H2S. Taking this substitute, green and purple sulfur bacteria oxidize the H2S into sulfate so they can use it to make food. These two bacteria are best friends when it comes to living with each other, as they usually coexist in aquatic environments. From odd plants, colorful algae, and mysterious bacteria, it is amazing how living things can thrive in our world.