If all goes according to plan, Tim Sharbel could wind up with a big reputation—as the guy who “turned off sex.”
That may not sound good, but in a world trying to feed 10 billion people in the face of climate change, Sharbel’s efforts to find the switch that allows plants to reproduce asexually could literally be a lifesaver.
It’s not that the U of S scientist is opposed to sex. He’s an evolutionary biologist, after all, and the mixing of genes from mothers and fathers is what makes evolution possible. But there is a very good reason for females to go it alone.
“If you’re a mother plant and you’re not perfectly adapted to your environment, then variability is a good thing because some of those offspring will be better adapted,” he said. “But if you are perfectly adapted to your environment, then it’s in your interest to have offspring that are genetically identical to you.”
The process in which female plants produce seeds all on their lonesome is called apomixis, a long-known but dimly understood alternative form of asexual reproduction. Getting a plant to clone itself would be a huge benefit for plant breeders and, if climate warming models prove accurate, for all of us. Climate change doesn’t just mean warmer temperatures, it means more extreme weather—more intense droughts or heatwaves—playing havoc with harvests. It also means pests moving into new territory and new strains of diseases suddenly bursting onto the scene.
All of that will keep plant breeders scrambling to quickly come up with new, more resilient varieties. However, quick is not part of the plant-breeding lexicon.
“Many of our crops are hybrid crops,” said Sharbel. “Take corn, for example. A company will have two different genotypes and they will inbreed these lines to make them as homozygous individually as possible. That takes a lot of time, typically about eight generations.”
And then you still have to cross these two lines to see if the resulting hybrid offspring express the traits you are after.
But what if you could skip all of that? What if—upon finding an individual plant with improved drought tolerance, better disease resistance, or some other desirable trait—you could get it to clone itself?
“If you could have an apomictic switch, then you could multiply anything as soon as you identify a phenotype you like,” said Sharbel, a professor in the Department of Plant Sciences. “It doesn’t matter how complex the genetics are behind it, you could just turn off sex and have the plant clone itself.
“To produce a new hybrid now takes years and many resources because you have to go through rounds of inbreeding and crossing. This would allow you to generate a complex hybrid in one generation.”
It’s hugely promising, but equally challenging.
Sharbel’s 21-member research team is one of the largest in the world studying this “evolutionary conundrum.” And that’s an apt description.
For starters, apomixis is intermittent. Sometimes females do it on their own and clone themselves, sometimes they’re fertilized by male pollen and produce seeds bearing genes from both parents. It’s also rare. Only about three dozen (well studied) flowering plants are known to be able to circumvent the normal (that is, sexual) process that creates embryos and then endosperm.
To shine a spotlight on this mysterious process, Sharbel’s teams are starting at square one: What genes are involved and what do they do?
To do that, they’ve capitalized on advances in genetic sequencing and adopted an intriguing line of attack that “considers apomixis like a disease in a plant population.” Working with apomictic species, such as Boecher’s Rock Cress, St. John’s Wort and Kentucky Bluegrass, they divide them into two groups—one reproducing sexually, the other using apomixis. They then take eggs from both and use “very advanced omics techniques” and lots of “high powered statistics” to find genes that are present in the apomictic group but not in the other.
“You look at thousands of individuals,” he explained. “If a gene is important, you expect to find it in every apomictic plant. And lo and behold, what we’ve discovered is high levels of conservation of these genes. Pretty much the only way you can explain this is that these genes are important for this trait.”
So far, they’ve found two “extremely hot candidates” in wild relatives of canola that Sharbel has been working on for years. One has been dubbed APOLLO (APOmixis-Linked LOcus) and the other UPGRADE (Unreduced Pollen GRAin DEvelopment), an equally hopeful name.
So have they found the switch that turns off sex? Maybe.
“Now we’re trying to figure out what role they play,” said Sharbel. “Genes can act in a number of ways. We have enough information to give us confidence that we can invest time and money in taking these genes and sticking them into corn and canola.
“But that’s a shot in the dark. So we also have a large number of experiments looking at different aspects of these genes. One example is what proteins are being produced by these genes. Another is what regulatory factors are involved. We’re trying to get as much information as possible.”
It’s a pursuit Sharbel, Montreal native, has been pursuing for two decades, mostly in Germany, where he obtained his PhD. He was recruited by the Global Institute for Food Security two years ago, drawn both by its mission and the U of S itself. (“This campus just rocks in terms of departments, researchers, companies that are involved, and so on.”)
Of course, he says, everyone has the same question: How soon will he find that switch?
“It’s biology, right? It could work in six months, it could work in 10 years. We don’t know but we’re very excited,” he said.
“My goal is to get it to work and then hand it off. Plant breeding is not what I specialize in.
There are people who are much better at that.
“Our role here is to be the discoverers—and we know how to do that.”