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Talking Biotech is a weekly podcast that uncovers the stories, ideas and research of people at the frontier of biology and engineering.
Each episode explores how science and technology will transform agriculture, protect the environment, and feed 10 billion people by 2050.
Interviews are led by Dr. Kevin Folta, a professor of molecular biology and genomics.
Kevin Folta (00:22)
Hi, everybody, and welcome to this week's Talking Biotech Podcast. Now, plants can't get up and walk away from stress or predators, so they've evolved sensitive systems to sense and in some cases anticipate changes in their environment. Now, there's sensors to light, to humidity, to touch, to gravity, to dozens of other prevailing factors that push information from the external environment into the nucleus, shaping gene expression and adapting.
To that change. Now, the fun part about this in today's era of synthetic biology is that the plant sensor and response systems are basically a toolbox. They're a template for synthetic innovation, as we can use their sense and response systems to work for us. Now, a number of plant-based sensors have been developed over the years. Here on Talking Biotech, we talked about plants that sense spent military munitions with.
Neal (00:58)
you
Kevin Folta (01:15)
Dr. Liz Rylot, way back in 2019. There's a few other good examples too. But today's guest will talk about his innovation, a return to episode 42, where you can hear him sing his tribute to biotechnology at the end of the episode if you go back. We're speaking with Dr. Neil Stewart. He's the professor in the plant department of plant sciences at the University of Tennessee and also the co-director of agricultural synthetic biology. So welcome back to the podcast, Dr. Stewart.
Neal (01:45)
Thanks, good to see you again, Captain.
Kevin Folta (01:47)
Yeah, that's always nice to see you. And this is a really cool innovation that I read, and I I have to say I missed the original press releases a little bit ago on this, but it's definitely worth following up on. And I guess I have to tell the punchline up front. So you've invented a potato plant that senses radiation to let us know it's there. So why do we need a plant radiation sensor?
Neal (02:12)
So this is part of a larger program to design, build and test phytosensors to report dangers. And so why do you need one against radiation as well? ⁓ Fukushima's one, Chernobyl's another. And ⁓ it's a continuing issue in ⁓ the world. So plants are photosynthetic, so they self-
⁓ you know energize and ⁓ that's that's that's why we did it but it's part of this larger program to to design ⁓ and ⁓ building tests are a lot of different types of fighters sensors
Kevin Folta (02:54)
That's cool, and let's review what other ones might be at the end. But I'm kind of interested in this idea as a radiation sensor, is that radiation isn't one thing, so what kind of radiation are we talking about here?
Neal (03:01)
Right.
So we approach this to ⁓ essentially assay ⁓ gamma radiation. So this is one of the ionizing ⁓ radiation types and it's what is given off at Fukushima in Chernobyl.
Kevin Folta (03:25)
Okay, so and you have done this in potato. Now that's an interest that's an interesting choice too. So so what's what makes potato the best host as a radiation sensor?
Neal (03:29)
writes.
Right, so this is Solanum tuberosum, so it's the commercial potato. So when I talk about potato, I'm mainly talking about the plant, not the tuber, right? ⁓ But when we were designing, we thought, what is our chassis? What is our plant type? We wanted something that was easily engineerable for both the nuclear engineering but also chloroplast engineering.
and plant that was kind of compact and bushy. And so we settled on potato and also like potatoes. it's, there's some personal, personal things there.
Kevin Folta (04:20)
Yeah, I'll have to send you some. I just harvested about a quarter acre of acre of yesterday and just I spent my morning bagging up for farmers market. But ⁓ what kind of potato is that? So you mean said it's a s regular s old selenium tu selanum tuberosum? It's just a Burbank russet or something?
Neal (04:25)
Okay.
Alright.
Right.
Right.
So now we're using ⁓ the cultivar deseret. So it's a smaller red skin potato. And the other nice thing about potato other than the engineering part and the form of it is that it ⁓ makes potatoes pretty quickly. So you can cycle it pretty quickly.
Kevin Folta (05:01)
Yeah, it's it's and it's a pretty durable plant too. I mean it's it yeah, I mean Florida's the ninth largest potato producing state and a lot of people don't know that. But we we produce a lot of potatoes here and I grow about a quarter acre over at our place and I love growing I it's one of my favorite crops to grow because it's magic. You you stick this little piece of potato in the ground and and ninety three days later you pull out this big bunch of potatoes. It's pretty cool. So so I I I I
Neal (05:04)
It is.
Nice.
Alright.
Right.
Exactly.
Kevin Folta (05:31)
was attracted to the magic of this. I think that's how I stumbled onto it. So ⁓ here's the kind of the big question though. So we know that ⁓ gamma radiation at certain doses causes damage to biological organisms. It damages us, damages bacteria. So does it make sense to have a sensor in an organism that's destroyed by the thing it's trying to sense?
Neal (05:35)
Okay.
So plants have in general higher radio tolerance than animals. so when we tested our potatoes against our potato plants against various levels of radiation, know, it's pretty healthy. It'll like 10 times the amount of radiation that would be lethal to humans. So yeah, you want to have your sensor.
in some sort of radio tolerant chassis.
Kevin Folta (06:27)
Yeah, that's cool. How how do we know that it's or w what makes it radio tolerant? I guess that's the big question.
Neal (06:33)
I don't know. don't know. ⁓
Plants, as you said in the introduction, plants can't get up and run away. So there's a lot of DNA repair ⁓ genes in plants. And that is kind of where we started off with building our sensor.
Kevin Folta (06:53)
And what about background radiation? I mean, we're continually hit by gamma radiation just at low levels. And so what makes that not respond to that?
Neal (06:59)
Right. Yeah.
Well, we don't know. We don't know that either. know, there probably is some sort of response, some sort of low-level response. You know, there's this idea that actually some ⁓ low-level radiation could actually be good for organisms because it does keep the DNA repair going. So when you have these double-stranded breaks, they're repaired. And so all the DNA repair...
mechanism is not completely off.
Kevin Folta (07:37)
We're speaking with Dr. Neil Stewart. He's a professor in the Department of Plant Sciences at the University of Tennessee. This is the Talking Biotech podcast. Thank you to New England Biolabs for your sponsorship, and we'll be back in just a moment.
And now we're back on the Talking Biotech podcast. We're speaking with Dr. Neil Stewart. He's a professor in the Department of Plant Sciences.
The co-director of agricultural synthetic biology at the University of Tennessee in lovely Knoxville, where I get up a few times a year. So we're talking about a plant radiation sensor, and that a potato plant has been genetically engineered to respond to gamma radiation, and this being a sensor of danger ⁓ that can be used to be placed into environments that may be challenging for human existence.
Let's get into the nuts and bolts of this because this is the part that's always exciting to me and this audience is how do you make a plant radiation sensor? Is it keying off the idea of the signals that alert the cell to DNA damage or what did what did you do?
Neal (08:44)
So for our phytosensor platform, we're looking at basically two things, sensing and reporting, right? So the easiest sense and report is something that the plant can sense in its leaves because that's also where you can see the report. So for a lot of our sensing ⁓ technology, we're using synthetic promoters. And so we've gone to plants.
and assess their promoters. And so what a promoter is for any organism is you think of it as a gene switch. It's turning on gene expression. And so promoters control gene expression in both ⁓ the tissue and also the timing. So these inducible promoters could be used to now drive a reporter gene.
right, if that makes sense. And so, of course, we went to DNA damage ⁓ genes and looked at their genes that regulate their expression. And so, the thing that we noted is that the full length, very long, like thousand base pair promoters are very weak. So that's why we turned to synthetic promoters.
Kevin Folta (10:09)
Okay, so when you're saying synthetic promoters, were you looking ⁓ based on were you did you develop these based upon say viral sequence or something that we know has a high level of expression and just kind of trial and error until you found something that was ⁓ really strong to drive the response?
Neal (10:26)
Yeah, that's a really good question. So we do use a very small snippet of a viral promoter ⁓ that is very strong for plants and that works in plants. And that's the 35S promoter, know, the 46 base pair kind of core promoter. ⁓ But our synthetic part is these ⁓ snippets of DNA, these motifs that could be
six base pairs to like 20 base pairs that affect transcription factor binding. So these are proteins that control expression. And we simply identify these and we multimerize them. In this case, we looked at a lot of different promoters from DNA repair genes and settled on RAD51 as our candidate.
and essentially tetramerized ⁓ a pretty small piece of DNA. And that's the one that was most effective in responding to radiation.
Kevin Folta (11:35)
Okay, so essentially you've re recreated a volume and an on off switch and volume knob to ⁓ that is attenuated by radiation exposure. And so this is a ⁓ what does rad fifty one typically do inside the cell?
Neal (11:50)
It's a DNA repair protein. So the gene controls ⁓ fixing double-stranded breaks in DNA.
Kevin Folta (11:59)
Yes, this is an important part of of the cell cycle. You replicate DNA or you have damage from environmental issues, the cell has to repair that before it proceeds. And so that's what this is. What about the ⁓ output side? You mentioned this idea of a reporter. And so what are reporter genes? And can you give us maybe a sense of a couple of them and their utility in molecular and synthetic biology?
Neal (12:02)
right.
Vvvvv
Right.
Right, so ⁓ there are a lot of reporter genes that are used in plants. The one that we've used is one that fluoresces green when exposed to blue or UV light. It's called the green fluorescent protein and it comes from jellyfish. And there have been lots of variants made to improve the properties. So...
this is the one we used and and the reason why we use the GFP is that it's it's it really has some unique spectral properties in in respect to the spectral properties that plants have
Kevin Folta (13:02)
Yeah.
Yeah, so the GFP protein is just one of these sets of reporter genes and other ones that we've used over the years are a thing called beta glucaronidase, which is gus, which gives us a blue precipitate when you but ⁓ and luciferase is cool because it's the firefly gene that when you but the downside of those i are with gus it's either lethal, so you gotta take the plant and kill it to see it. And then the other one is you gotta sp spray so many
Neal (13:13)
Right.
They are. Yeah.
Kevin Folta (13:30)
reagents on the plant to get it to flor to see it. GFP is just is is a autonomous. You hit it with a beam you hit it with a photon of blue, it gives you a photon of green. Yeah, so so that's that's just to clarify for the audience. So the problem I see though, that I would anticipate is how do you observe this? I mean you have to go out in the field with a blue light and look for green.
Neal (13:36)
Right.
So, you know, all of our stuff was confined to the laboratory. And so we built a laser range using ⁓ various diode lasers and then captured fluorescence. Because fluorescence is the transduction of ⁓ a higher energy light to lower energy light. So this has some limitations in the field.
So you could use ⁓ some natural pigment genes like ⁓ betelane. So that's a beet protein and it creates a red color. And that would maybe be the way to go in the next step. But it's pretty easy. You just swap the reporter gene.
Kevin Folta (14:45)
Yeah, so it's just a different way to visualize your your output. So you're doing proof of concept in the laboratory with with an im with a good GFP based ⁓ solution. That sounds good. And how fast is it? I mean, that seems to be the other problem that if you're going to get a ⁓ response to radiation, like is it safe? It it probably isn't good enough to wait a day and come back. You know, does is it a reasonably quick promoter?
Neal (15:12)
So yeah, so transcription and translation are not fast processes, as you say. It takes about 48 hours to actually see it. So these are good for applications where ⁓ it's almost like a steady state, right? ⁓ Radiation dose. But still, you can think about applications.
Kevin Folta (15:22)
Yeah, so
Mm-hmm.
Neal (15:39)
⁓ where it's still good to have this reporter.
Kevin Folta (15:42)
Yeah, so maybe it's not the best way to say, should I go in there? But it's good it's on the input side. But to put a bunch in there and say, after time, it appears it is now safe to go in there. So yeah. Yeah, so you have a robot go in and plant it or ⁓ drone drop it and whatever, and then you can look to see if yeah, no, I'm with ya, I get it. And is it is it quantitative? Does it tell you how much radiation or is it just kind of ⁓ plus or minus?
Neal (15:54)
Right, yeah exactly. Yeah, so as a monitor.
Right. Yeah.
Yeah,
I think it's semi quantitative. And so we looked at ⁓ kind of low level to very high level. And so now we have some other promoters where we can go even lower than what we published on. So we can increase the sensitivity.
Kevin Folta (16:31)
Yeah, that's really cool. Well you also can you know play with the promoter now too and get that get that even higher. And I guess that
Neal (16:35)
Right, Yeah,
once you know something works, then you can make it work better. Yeah. Right.
Kevin Folta (16:39)
That's right. You can make the wheel rounder, right? And but what
you know, but let's even go outside of radiation detection per se. Now that you've got a sensor that detects gamma radiation, what other applications could potentially exploit that?
Neal (16:47)
Okay, yeah.
So you know we've thought about a ⁓ kind of a house plant that may be a radon sensor. So that's alpha radiation. still an ionizing radiation. ⁓ But you know we've also thought, especially since NASA's ⁓ discussed going to Mars, any sort of long space flight, you're going to get ionizing radiation in various doses and pulses for astronauts.
So, ⁓ you know, maybe this could be actually an edible sensor where you're making potatoes ⁓ for ⁓ trips to Mars. It's kind of like Matt Damon, you know, and the Martian. So, yeah. Yeah.
Kevin Folta (17:38)
That's right. E eat the green potato chips, right? If you shine a blue light on them, you could Yeah. Well that
that's that's all pretty interesting stuff. So you mentioned that you were working on other types of sensors, biological sensors. So what are some of the other ones on the drawing board or maybe other ones you've already published?
Neal (17:52)
Right. Right.
So yeah, so we've done a lot on ⁓ sensors for plant diseases. Okay, so we've looked at a lot of those. ⁓ Chemicals, so chemicals that could be toxic chemicals, know, letting the plant tell you where and what those are doing to the plant. ⁓ But you could think of ⁓ any number of, and even agricultural chemicals.
where you're looking at residues. ⁓ we think that we can make plants do a lot of things that they've never really done before.
Kevin Folta (18:37)
Yeah, that's been kind of my dream is to develop a petunia or something like this that you would use as a sensor in an agricultural field, because I would love to know that my nitrogen rates are exactly right. And so having the having a plant that would tell me in this spot that I can that you have X amount of nitrogen that's native to the soil or you need more phosphorus or whatever you'd need, to have a plant that would give you a a a purple flower that would be a degree of purple, you'd hold it up to your
Neal (18:48)
Right.
Kevin Folta (19:05)
chart and say, here's what I need to add. Those kinds of ideas are so good, but I I don't know that anyone is doing them. And then I don't know that I'm there are some. Okay.
Neal (19:13)
you know, there is some. Yes,
so there are companies that are working on this very thing as far as fertility, soil fertility, and now being able to read stuff from a satellite. And I think that's where the world is going. Yeah.
Kevin Folta (19:27)
Yeah. Yeah, no ⁓ it's got to. I mean we we don't have more
land. We gotta play with the stuff we got. And you know, here down in Florida we're growing plants essentially hydroponically, we're growing plants in sand. ⁓ pH and and nutrients are always an issue. both because of plants, plus you don't want to stick any more into the
Neal (19:38)
Yeah,
Kevin Folta (19:47)
Well, Dr. Neil Stewart, very nice to see you again. This is pretty cool stuff, really exciting to see innovation happening in plant space and ⁓ wish you well. And if people want to know more about this particular project, where can they find more information?
Neal (20:01)
Probably the easiest way is just to Google phyto sensor, P-H-Y-T-O-S-E-N-S-O-R. So phyto means plant and sensor means sensor. University of Tennessee.
Kevin Folta (20:13)
Perfect.
No, absolutely perfect. Well, thank you very much for joining me. Good to see you. Still playing guitar.
Neal (20:21)
Still playing guitar, still writing songs. In fact, I do have a potato Christmas song. That's my, and it's on Reverb Nation.
Kevin Folta (20:23)
Awesome. Well
Okay.
It's on reverb nation. Can I put a little piece of it at the end of the can I may I put a chip of it at the end of this podcast? All right, that sounds good. Well, thank you very much for joining me. And for all the folks listening, thank you very much for listening to another episode of the Talking Biotech podcast as we are ⁓ at around episode 500 and officially ⁓ 11 years completed into the twelfth year of weekly podcasts.
Neal (20:40)
I think so. think I can send you a snippet.
Alrighty, you got it.
Kevin Folta (21:02)
So, this is the Talking Biotech podcast, and we'll talk to you again next week.