Phytochromes: the most important twitch on the planet – Audio
Phytochromes helping plants use light
Richard Vierstra, Professor
Department of Genetics
UW-Madison College of Agricultural and Life Sciences
vierstra@wisc.edu
(608) 262-8215, (608) 262-0307
8:30 – Total Time
0:18 – A definition of phytochromes
0:53 – How phytochromes work
1:22 – How plants interpret light
2:04 – What is shade avoidance
2:43 – Managing plants for higher yields
3:10 – Increased yield, increased resource demand
3:36 – An applied example
4:30 – What a new corn field will look like
5:05 – Most plants use phytocromes
5:29 – The technology is now
6:01 – Moving out of the lab
6:32 – How the discoveries were made
7:09 – The ah-ha! moment
7:37 – Tools of the research trade
8:21 – Lead out
TRANSCRIPT
Sevie Kenyon: Rick, can you tell us what this molecule is that you work with?
Richard Vierstra: I work on this amazing photoreceptor that’s called phytochrome. And, plants being sessile, which means that can’t move around, have really adopted great ways for them to capture food. And one way, is to survive so they know when spring comes, when summer s around, and eventually when fall, so they know when to germinate, grow, flower, and eventually die. So, they attrain all this to the light environment using these amazing photoreceptors.
Sevie Kenyon: And Rick, your working at the molecular here, can you tell us what goes on at that point in the plant?
Richard Vierstra: Ok so these phytochromes, what they have is a pigment inside them that’s buried inside the molecule. So when that pigment absorbs light it twitches, and I would argue that this is probably the most important twitch on the planet because when that twitch happens, plants turn green. They germinate, they become photosynthetic, they flower, and eventually they senesce. And they do that by measuring that twitch.
Sevie Kenyon: So what are these molecules actually doing?
Richard Vierstra: Ok, so when they twitch, what the chromophore does is it flips inside the protein coat of this photoreceptor. There is a ripple effect upon this twitch that leads to eventually an output domain that tells the plant that the lights on, or the lights off. And it can also tell the plant how long the light’s been on, it can tell the plant how long the light’s been off, and it can also tell the plant what the color of the light is. So it can actually allow the plant to sense whether it’s in full sun or whether it’s being shaded by other plants. It turns out that is a really important process in agriculture. It’s called shade avoidance.
Sevie Kenyon: And Rick, can you further describe what shade avoidance means to the agricultural community?
Richard Vierstra: Take plants and you put them in a dark corner, they will grow tall and spindly, and what the plant is trying to do is it’s trying to grow towards situations in which there’s better light. And this happens in a field. So when you have a lot of crops growing together in close situations, they are measuring not only whether a plant is above them, but they’re also measuring whether there’s a plant alongside them. It does this by measuring the twitch of phytochromes, and so it can then sense competition, so if there’s competition, then what’ll happen, it will start growing taller.
Sevie Kenyon: And Rick, as you work with these molecules, are you also looking at ways to manage this process?
Richard Vierstra: Now the problem with shade avoidance is that the plant is spending all this time making stems so it can grow tall instead of making food that we eat. We want to pack a lot of plants in, but we want to suppress the shade avoidance response. To do that, we have to manipulate phytochromes so that the plant sees light in a different way.
Sevie Kenyon: Does this also then increase yields and increase demands on soil and water resources required?
Richard Vierstra: All the demands will grow up as your increasing let’s say, crop density. But, if we can manipulate the phytochrome system, then we can maybe keep the plants in check in terms of how much they take out of the soil, and how big they grow. And therefore, if we can suppress how big they grow, maybe we can divert more of the carbon, for example, that they fix, into the thing we eat, into the seeds and fruits and things like that.
Sevie Kenyon: Can you give us an example of this?
Richard Vierstra: Well, a good example is corn. Corn right now, when you pack them in, they actually start growing taller and taller and taller. And you know, the idea now that many of the Ag. Companies want to increase corn production by fifty percent? How are they going to do that? They are going to increase the density of corn in the field by fifty percent. So that is then going to really accentuate the shade avoidance response. Which means corn is going to grow taller and taller and taller, as it gets more and more crowded. And so we have to figure out ways to suppress that. So our understanding of phytochromes hopefully will lead to solutions. We’ve actually now got collaborative projects where we’re trying to put these engineered phytochromes into corn. So we should be starting next fall, where we’re going to be engineering the phytochrome system in corn, in lines that will eventually be used for breeding.
Sevie Kenyon: Based on what you know about this, what might this new cornfield look like?
Richard Vierstra: Hopefully they’d be very short. So they’d be very packed rows, and the plants would be short, but each one would produce the same ear, and the same size ear. We’re also hoping that we’ll eventually develop lines of different species. For example, that will flower at different times of the year. So we might be able to get Chrysanthemums to bloom in the summer rather than in the spring, or we might be able to get Poinsettias to bloom at different times of year. So eventually I think with this phytochrome system we hope to start manipulating other things besides shade avoidance.
Sevie Kenyon: Is this process fairly uniform across plants in general?
Richard Vierstra: Yeah, many plants have very strong shade avoidance responses. Almost all the major crops do— wheat, corn, barley, tomatoes. Anything that you try to pack in at high density, they will try to avoid competition by growing tall.
Sevie Kenyon: Well Rick, maybe I can get you to look into your crystal ball a little bit. What o you see, and how long may this take before we can apply it?
Richard Vierstra: Well we’re actually hoping to try to start doing that now. So in the last few years my lab has been trying to understand how phytochromes work at the atomic level. We’re now starting to engineer phytochromes so that they see light in different ways; so they’re more active or less active, or stay active longer or stay active for shorter period of time. In that case we can start manipulating how plants perceive their light environment. And we’re at that point of doing it now.
Sevie Kenyon: At these early stages Rick, is this work being done in greenhouse or is it being done outside somewhere?
Richard Vierstra: So right now all our work is being done in growth chambers inside environments using model organisms. So we’ve recently taken our understandings of the atomic level, and moved that understanding into plant phytochromes, which we’ve now started to reengineer how they work. We’ve now, for example, developed phytochromes that are poorly active. We’ve developed one that’s fifty times more active than the wild type. So it needs fifty times less light to actually tell the plant that the light’s on.
Sevie Kenyon: Rick maybe you can tell us a little bit about how you made these discoveries.
Richard Vierstra: We started off by trying to understand how phytochromes work, both genetically at the biochemical level. We got lucky in that, as we started finding models of these phytochromes in bacteria. And we started using those as models to understand the structure. We’ve then progressed through sort of the evolutionary tree. We started out with very primitive bacteria, we moved into Cyanobacteria, we moved into fungi, and now we’ve actually moved into plants. So now we understand from this tree how phytochromes work. From there, we are now starting to engineer plant phytochromes.
Sevie Kenyon: Rick I’m a little curious, what was this lucky moment that caused this revelation?
Richard Vierstra: The lucky moment was really getting the first structure, which came from a bacterium that actually lives in a nuclear reactor. The “Ah Ha” moment for us was seeing the first structure. So we could actually see where the chromophore was, how it might work, we didn’t know all the details at the time, but it was almost for us like seeing god. Where we final had something we had been searching for, for a long period of time.
Sevie Kenyon: And Rick, maybe you can describe some of the instrumentations and processes you use.
Richard Vierstra: Yeah so we use a lot of sophisticated instruments that you can only find in a very few places in the world. So we use what’s called a nuclear magnetic resonance spectroscopy, the UW Madison is lucky to be one of the experts, and they have a whole suite of spectrometers that we’ve used. We’ve used another technique called X-ray crystallography, and we’ve actually sent our materials down to the fermilabs in Argon, Illinois were they shoot x-rays at very high speeds and figure out crystal structures. We’ve been also using single particle electro-microscopy using a national laboratory in Brookhaven. So these are facilities that we’ve been able to tap to answer some very fundamental questions about how plants live.
Sevie Kenyon: We’ve been visiting with Rick Vierstra, Department of Genetics, University of Wisconsin and the College of Agricultural and Life Sciences, Madison, Wisconsin, and I’m Sevie Kenyon.