Menaka Wilhelm

Like many good ones, this story starts in a greenhouse.

Sarah Sharman

OK! So sunny, warm,

Menaka

Yeah – and this is a specific greenhouse. One I went to in Albany, California, just Northwest of Berkeley. It’s a rooftop greenhouse, where researchers grow plants for their work with the US Department of Agriculture

Sarah

Oh official!

Menaka

Exactly. And I want to point out one kind of tree growing in this greenhouse. It’s the rubber tree, a species called Hevea brasiliensis.

Sarah

So this is the tree where we get rubber for tires, rubber gloves, and also rubber boots.

Menaka

Exactly – and there are about a dozen rubber trees here in this greenhouse. They’re around six feet tall, with big, football-shaped leaves the size of your hand. And up and down their slim, tan trunks, are diagonal slashes.

Sarah

And that pattern? It’s not part of their bark.

Menaka

Growers cut those slashes – this is the first step in making rubber. It’s called tapping a rubber tree – a little like tapping a maple tree for sap, to make maple syrup. When you tap a rubber tree, liquid latex drains out of the bark.

Sarah

So, you collect that liquid, then process it into rubber. So, the trees are in the greenhouse for studies,

Menaka

Yeah, but the rubber trees aren’t our main event. They’re here for comparative experiments with the plant that’s really the star of the show because it makes rubber too.

Sarah

A spotlight-stealing shrub — Parthenium argentatum.

Menaka

Yeah. This shrub’s common name is guayule. It’s a more sustainable, climate-resilient plant, and researchers are betting that one day, this shrub could give the rubber tree a bit of a run for its money. So next door to those rubber trees? This greenhouse has another room. It’s full of these guayule shrubs.

<THEME>

Sarah

This is a special episode of Tiny Expeditions from the HudsonAlpha Institute for Biotechnology,

Menaka

And Genome Insider, from the Joint Genome Institute.

Sarah

I’m Dr. Sarah Sharman,

Menaka

And I’m Menaka Wilhelm. The JGI and HudsonAlpha work together on lots of projects,

Sarah

Including this one! So we’ve teamed up for this episode.

Menaka

It’s the story of the researchers who are working to make a shrubbier version of rubber.

Sarah

Because that shrub just might grow better in our warming world.

Menaka

And it could be a useful crop in multiple ways. Researchers are hoping to harvest rubber from its stems, then convert what’s leftover into other chemicals and fuels.

Sarah

So we’ll meet a few of the people behind that project. There’s a full team of researchers working with the JGI and HudsonAlpha on this.

Menaka

Yep. They’re from the Boyce Thompson Institute at Cornell University, Bridgestone, New Mexico State University, and the US Department of Agriculture. And they’re all very interested in this guayule shrub.

Sarah

So first — let’s start with why we need more sources of rubber.

Menaka

To be clear, there are two different kinds of rubber in our world.

Sarah

There’s synthetic rubber,

Menaka

Made from petroleum,

Sarah

And natural rubber,

Menaka

Which comes from plants.

Sarah

Synthetic rubber works well for lots of things. But for durability, natural rubber wins out. It’s stronger, and more resilient against wear. A lot of stuff in our world depends on it. I heard about this from Dave Dierig – he’s a plant geneticist working on this project at Bridgestone. As in, Bridgestone Tires.

Dave Dierig

So most tires, anything larger than a car tire, has a high percentage of natural rubber in it. Airplane tires are all natural rubber because synthetic rubber really can’t do the same things that natural rubber does.

Sarah

As one example, natural rubber stays flexible even at low temperatures. That’s why it’s key for airplane tires — they see a big temperature range. But there’s a pretty big problem with natural rubber.

Menaka

Almost all natural rubber comes from just one species of tree.

Sarah

Hevea brasiliensis, that species you saw in the USDA greenhouse.

Menaka

It’s a tree that provides a bunch of rubber — but it’s also a tree that’s in trouble.

Sarah

For starters? Rubber trees are all genetically identical. They’re like banana trees – they’re all clones.

Dave Dierig

So we’re concerned about all the risks that natural rubber plantations have right now with diseases. You know, it’s a tree, it’s a clonal crop.

Sarah

On a rubber tree plantation, every single tree has the same defenses against disease. If a tough fungus comes through? It can wipe out an entire plot of trees at once.

Menaka

And that’s happened.

Sarah

Yeah – rubber trees are native to Brazil. But they really don’t grow there anymore. A disease called South American leaf blight has pretty much squashed commercial rubber production in South America. So now, most commercial rubber grows in Southeast Asia.  There, it’s safe from disease, for now. But it’s not safe from other issues.

Dave Dierig

Climate change is another issue that we’re worried about,

Sarah

Climate change is making both droughts and floods more extreme.

Menaka

Both are bad news for rubber trees.

Sarah

And Dave pointed out one more risk.

Dave Dierig

Labor shortages, because you have to go around to each tree on a daily basis and tap the tree to get the rubber out. So, it’s very, very labor intensive,

Menaka

So, yeah – the rubber trees are in a bit of a pickle.

Sarah

But natural rubber is hugely important for lots of industries. So Dave is looking elsewhere.

Dave Dierig

Every tire company is looking for some kind of alternate source or supplemental source of natural rubber.

Menaka

And actually, we’ve made rubber – at scale — from other plants before.

Sarah

Because lots of plants make rubber, actually.

Menaka

There’s some rubber in sunflower leaves and lettuce. And of course – there’s a shrub that makes a lot of rubber, that’s also high quality.

Sarah

Enter, guayule.

Menaka

That’s G-U-A-Y-U-L-E

Sarah

And pronounced why-yule-ee.

Menaka

The shrub that makes rubber!

Sarah

If we’re being honest, when you see guayule, it looks a bit forgettable.

Menaka

Truly, it’s a very shrubby desert plant. A lot of people describe it as tumbleweed-y. It grows about a foot or so off the ground, with little sage-green leaves.

Andrew Nelson

It’s not particularly showy, even the flowers don’t really look like much,

Menaka

Andrew Nelson is a plant biologist at the Boyce Thompson Institute at Cornell University. He’s leading this project. For Andrew, guayule’s humble appearance is not a problem.

Andrew Nelson

What’s interesting about guayule is that it produces an insane amount of rubber. It stocks up a lot of rubber, in its stems.

Menaka

The stems can have six or eight percent rubber. Not bad for a dusty desert shrub!

Sarah

And guayule has a bunch of advantages that could make it cost-effective and more sustainable in the long run.

Menaka

Unlike the rubber tree, there are different lines of guayule. So it has more potential for genetic diversity, which means more defense against disease.

Sarah

It’s native to a hot, desert area — Northern Mexico to the southwestern US. That means more resilience against climate change,

Menaka

Plus — guayule grows with less water than many row crops like alfalfa or corn.

Sarah

A more sustainable crop for farmers in desert areas.

Menaka

And harvesting guayule isn’t labor intensive the way tapping rubber trees is – you can cut stalks and stems from a bunch of shrubs at once, with help from machines.

Sarah

So, it’s a shrub that solves a lot of the rubber tree’s problems.

Andrew Nelson

In addition, when the rubber has been extracted from these plants, you can actually use what’s left over as kind of a natural biofuel.

Menaka

So you could grow guayule, then process it into two renewable products – rubber, and also chemicals!

Sarah

Wow, the wonder-shrub guayule!

Menaka

Dreamy.

Sarah

And actually, people have used the guayule plant throughout history. I looked into that for a piece I wrote for HudsonAlpha’s blog, Everyday DNA.

Menaka

Linked in the show notes!

Sarah

So let’s start with the first time guayule shows up in western records. That’s in the 1500’s… when colonizers from Spain noticed Aztec people playing with rubber balls made from guayule!

Menaka

And guayule has actually been mass-produced before, too, right?

Sarah

Yeah – in the early 1900’s, it was. Industrialists like John D. Rockefeller created a firm to turn guayule into rubber. They harvested wild guayule from Mexico, and it kind of worked. We used a lot less rubber then — but by 1910, about half of all US rubber was from that wild guayule.

Menaka

Wild guayule is quite the tongue twister. At this point, it sounds like it’s catching on.

Sarah

But then, between Mexico’s revolutions and over-harvesting, that wild guayule? That all fizzled out.

Menaka

Ah.

Sarah

And there was actually another time where lots of people worked on making rubber from guayule – World War II. The US got cut off from sourcing rubber from Asia after Japan seized rubber plantations. So, congress funded something called the Emergency Rubber Project. During that project, researchers planted and grew over 32,000 acres of guayule.

Menaka

So the goal was to work out how to farm a domestic, natural source of rubber.

Sarah

Right. But the push for that project ended with the war. Once we could get natural rubber from Asia again, that’s what we did.

Menaka

So no one has really figured out how to grow guayule … so that it makes enough rubber … to be a large-scale profitable crop.

Sarah

No. But understanding this plant better could change that! If these researchers can figure out how guayule makes rubber, they could boost its rubber production. And still keep all those other strengths guayule brings to the table.

Menaka

So as with many projects at the JGI and HudsonAlpha, researchers are aiming for better understanding in the form of genomics! Here’s Andrew Nelson again.

Andrew Nelson

So with Bridgestone, David Dierig, at Bridgestone, Colleen McMahan at USDA and myself, we, we spearheaded this proposal for JGI to actually sequence the genomes of these plants.

Menaka

Historically, it’s been hard to sequence guayule. It’s got a really big genome.

Sarah

But HudsonAlpha and the JGI have the expertise!

Andrew Nelson

And if we want to figure out like, what is actually working to turn on the rubber biosynthesis pathway in these plants and, um, you know, figure out all the molecular components, you know, we, we really need a genome.

Menaka

And actually, they’re not just stopping at one genome.

Sarah

They’ll sequence and analyze multiple plants.

Menaka

Right. In just a bit, we’ll head back to the greenhouse where we first started out, the one that’s growing guayule alongside rubber trees. It’s Colleen McMahan — the third researcher Andrew Nelson just shouted out — who showed me around there. She showed me the plants that will get sequenced, and she’s got lots to say about what the guayule genome will let this team do.

<Genome Insider Trailer>

Menaka

To recap where we’ve been so far – right now, we rely on pretty much only one way to make natural rubber. The rubber tree, Hevea brasiliensis.

Sarah

But it’s also a tree that’s up against disease and climate change.

Menaka

So researchers are trying to find other rubber-producing plants. And the guayule shrub is a great candidate.

Sarah

It grows in a harsh, desert climate.

Menaka

It’s easier to harvest.

Sarah

And it’s got more genetic diversity than the rubber tree.

Menaka

Yeah – and I actually saw some of that diversity firsthand.

Sarah

So cool. Set the scene for us.

Menaka

Of course. So this is back at the USDA greenhouse that we started this episode with. It’s a pretty big, rooftop greenhouse at the USDA building in Albany, California. Plenty of sunlight comes in. Colleen McMahan is showing me around. She’s a research chemist at the USDA who is also part of this project. So we’re in the greenhouse, and she wheels out a cart with three different potted guayule plants.

Colleen McMahan

There are three different, guayule varieties in the initial phase of the project. And the three plants you see right here are those three plants.

Menaka

They’re all little potted shrubs, about the size of a basketball, but they look different by eye. One is a dustier green, more like a sage plant. Another is a much brighter green, think, like basil. And the third is somewhere right in between those two.

Sarah

And I’d bet their differences go beyond their color.

Menaka

Right. Here’s Colleen.

Colleen McMahan

They’re quite different genetically as well. And so the information that we get from those plants will be huge.

Menaka

Overall, they want to understand how to get guayule to make more rubber. But it’s also important to keep its other good qualities in tact. So the idea.. is to look at a handful of plants, and see the genetics behind a variety of strengths.

Sarah

OK, to get a better picture overall.

Menaka

Right. These plants each produce different amounts of rubber and have unique disease resistance.

Sarah

Nice.

Menaka

Those are the broad strokes. But I want to get just a little more specific about these plants, actually.

Sarah

Let’s do it.

Menaka

1. So these plants are actually very different in specific ways — It turns out, the greenest plant I saw is quite different from the other two, the ones that were more sagey green.

Sarah

Ok. One that’s different, two that are more similar. following so far.

Menaka

Great. So let’s start with that greener plant. It’s a diploid plant – it’s got two sets of chromosomes, and it reproduces by crossing with other plants. Chen Dong is a researcher who works with Colleen, and she told me the reason they want to look at that plant, is

Chen Dong

So we can just have a pure genome of guayule,

Menaka

So just a clear, complete genome. This is like our basic version of guayule.

Sarah

And what about the other two plants?

Menaka

Yeah – this is where our picture gets even more technical. The ones that are dustier green, that are more similar in color — they reproduce asexually. They’re both tetraploid plants, which means they’ve got four copies of their chromosomes.

Sarah

So double the chromosomes of our first plant.

Menaka

Yes!

Chen Dong

And these are the ones that, Bridgestone uses for, breeding.

Menaka

Bridgestone is interested in diploid plants, too – but these two lines are specifically part of their breeding program. And each of these tetraploid plants are important to this study for their own reasons. The plant that’s the most sagey green — it’s the smallest, but it produces a bunch of rubber.

Sarah

Seems like a great plant to work with, in this quest to crank up rubber production.

Menaka

And the other tetraploid plant is interesting for a different reason. They’ve already figured out how to edit its genes.

Colleen McMahan

So we can genetically transform the plant. We’ve had success with doing that with a number of genes and in entire pathways in a couple of cases.

Sarah

So they’re already able to tweak this plant.

Menaka

Right – the question is just which tweaks to make, for example, to boost the pathway that produces rubber.

Sarah

And that’s where all of JGI and HudsonAlpha’s genomic information comes in.

Menaka

Exactly. Beyond just getting the sequence of guayule’s genome, JGI and HudsonAlpha will help this team work out which genes are there, how they’re turned on and off, and what they do.

Sarah

Lots of information about how guayule makes rubber.

Menaka

So Colleen and Chen will get even more information from editing this line of plants. They’ll be able to find important genes, then basically delete them with CRISPR gene editing, to see exactly how important they are.

Chen Dong

We want to confirm the functionality of these genes that we use CRISPR to narrow down these genes and see what is happening to these plants.

Sarah

So cool.

Menaka

Right! But Colleen did point out – even though these greenhouse studies will give them a ton of information, there’s actually still more to the story.

Colleen McMahan

So there’s a really important, genetics-by-environment component for guayule, and that’s one of the areas that we’re studying in this project is, what happens to the gene expression as the environment changes. And we’re really excited about having the opportunity to look at that.

Menaka

So guayule growing in a controlled greenhouse will do things differently than guayule growing outside, in a field.

Sarah

Which brings us to our last researcher of this episode. He’s with Bridgestone, growing guayule in the field.

Von Mark Cruz

So, I’m Mark Cruz. I’m a plant breeder at Bridgestone Americas, in Eloy, Arizona.

Sarah

Mark works with Bridgestone at its research farm in Arizona. It’s two hundred and eighty-one acres of these hardy guayule shrubs. Picture green shrubs, about a foot tall, filed in organized rows in the dirt.

Menaka

A whole club of shrubs!

Sarah

That farm grows guayule for lots of projects. For this project, Mark is growing the same three lines of plants as Colleen and Chen. So he’ll be able to compare these field samples with their greenhouse plants, and see what changes outdoors.

Von Mark Cruz

So knowing the gene expression patterns and how those correlate to rubber production will really help. So our goal is to determine those gene expressions at the different locations, and maybe in the future we can link it to protein expression levels too.

Sarah

Like Colleen and Chen, they’ll take a look at the genes that help guayule make rubber. Mark is also interested in making guayule a hardier crop – one that more farmers can grow in more places. So he’s also looking at the genes that make this shrub cold-tolerant.

Menaka

That sounds like it means even more testing.

Sarah

Exactly. Besides that farm in Eloy, they’re growing guayule in two other field spots for even more comparison. So all in all, Mark and his team are growing these strains in three places, outside

Von Mark Cruz

In Salinas, in Parlier California, and Eloy, Arizona. And we, so basically I’m responsible for the field trials, and then we send the tissues to Cornell and Boyce Thompson.

Sarah

So by Cornell, Mark means he sends his samples over to Andrew Nelson.

Menaka

Right –  the plant biologist at the Boyce Thompson Institute, who told us a bit about guayule earlier in this episode.

Sarah

Yeah. Andrew’s lab will help analyze those samples. The JGI and HudsonAlpha will help too.

Menaka

Ah. We’ve come all the way full circle. Must be nearly time to end this episode.

Sarah

Yep, I think we’ve just about covered it. We’ve gone from trouble with the rubber tree to the guayule shrub that could help.

Menaka

And we’ve seen how this team will use greenhouse plants, field trials and a whole bunch of analysis to understand the genes that matter for growing guayule, and boosting its rubber content.

Sarah

To grow a reliable, sustainable version of rubber – that also supports biofuels.

Menaka

So Sarah, now that we’re pretty much done, I realize I’ve waited this entire episode to bring something else up.

Sarah

OK?

Menaka

In terms of naming. I know we talked guayule, but like, it’s a shrub, that can make rubber – so do you think…this version of rubber should be called… shrubber?

Sarah

Maybe? Seems like it’s past time to run the credits.

<THEME>

Sarah

Tiny Expeditions is a production of the HudsonAlpha Institute for Biotechnology, a non-profit research institution located in Huntsville, Alabama.

Menaka

Genome Insider is a production of the Joint Genome Institute, a user facility of the US Department of Energy Office of Science located at Lawrence Berkeley National Lab in Berkeley, California.

Sarah

This episode was written and produced by Menaka Wilhelm.

Menaka

Ashleigh Papp reported the interviews with researchers Dave Dierig, Mark Cruz, Chen Dong, and Colleen McMahan.

Sarah

AJ Bouchie reported the interview with Andrew Nelson.

Menaka

We had production help from Chris Powell, Massie Ballon, Allison Joy, Ingrid Ockert and Graham Rutherford.

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Thanks for tuning in – until next time!