Scientists may have discovered a whole new plant language. According to a new study, published today in Science, a parasitic plant called the strangleweed is capable of not only sucking out genetic material from the host plant it invades, but also injecting its own genetic material into its host. This, the researchers say, could simply be a means by which these organisms obtain energy from one another. But a far more interesting possibility is the idea that this might represent an entirely new form of plant communication — one that might give humans an edge when trying to curb invasions from parasitic plants.
"The typical way that plants communicate is through chemicals that they release through their leaves and roots," says James Westwood, a plant physiologist at Harvard University and a co-author of the study. "So to find out that there is an exchange of RNA" — the intermediary form of genetic information that fills the gap between DNA and proteins — "is a new concept that hasn’t been explored at all."
HACKING THE HOST PLANTS’ ENTIRE SYSTEM
Beyond the novelty of this finding, however, lie the potential agricultural applications, Westwood says. Researchers might be able to use the exchange of RNA to provide host plants with their very own defense mechanism.
In the study, Westwood’s team sequenced tissue samples from host tomato plants and strangleweed, which invade various plant species by wrapping themselves around a host and invading their vascular system. Both the strangleweed and the tomato plants’ genome have already been fully sequenced, so researchers were able to compare the RNAs contained in samples with corresponding DNA sequences in the genome. "We figured it out by process of elimination, and sorting out the sequences that weren’t substantially different from those in the full genome," Westwood says. Using this technique, the researchers determined that thousands of RNA sequences are likely exchanged between host and parasite during the invasion process.
"It’s surprising for a number of reasons," Westwood says. "The first being that if you think of a parasite as truly being a parasite, you wouldn’t expect to see movement of genetic material into the host — just the parasite sucking nutrients from the host."
And then there's the sheer volume of information being exchanged. Westwood’s team had previously been able to identify a few RNA sequences in parasite tissues. But the fact that thousands of bulky RNAs are potentially exchanged between the plants is astonishing, Westwood says. "It’s such a substantial amount of movement."
And because the materials being exchanged are really information molecules, it’s possible that the parasite is using its own RNAs for espionage, as well as for hacking the host plants’ entire system. "The parasite is basically sending information into the enemy’s house," Westwood says — information that can soften cell walls, for example, making it easier for the parasite to invade the host and make connections. "It’s very logical the RNAs would be working to help the parasite establish itself in the host," he says. And it’s this possibility that opens up so many doors for parasite control.
"What you could do is create a host crop that produces short RNA sequences that are specific against the parasite — you’d be helping it build its own defense system," he says. At the moment, farmers use herbicides to prevent strangleweed from ravaging tomato plants, alfalfa, and cranberry plants. So using this exchange of genetic material to our advantage could avoid these types of chemicals.
"WITH EXTENSIVE RNA MOVEMENT, MANY PARASITE PROCESSES COULD BE TARGETED IN CONTROL STRATEGIES."
Creating similar genetic weapons has actually been attempted with individual genes in the past, says Neelima Sinha, a plant biologist at the University of California Davis who did not participate in the study. But "this report now suggests that with extensive RNA movement, many parasite processes could be targeted in control strategies."
Unfortunately, researchers haven’t proved that the exchanged RNAs are used as information yet, so it’s possible they’re way off track. But because of the inherent nature of RNAs, Westwood thinks it’s likely that the host plants are producing proteins using each other’s genetic information. "It’s like stealing memos from the competition," Westwood says. "You can either read them or burn the paper as fuel."
For obvious reasons, Westwood is hoping for the former.
"WE THOUGHT 'MAYBE WE COULD GET PUBLISHED IN SCIENCE!'"
But before anyone can even consider creating plants with built-in defense mechanisms, Westwood and his team will have to demonstrate that the exchanged RNAs are truly being encoded by recipient plants. This won’t be easy, Westwood says, because researchers will have to distinguish the proteins that the parasite is making thanks to its own RNA from the proteins that it might be making thanks to host RNAs. "It is more challenging to definitely answer whether a protein has been made from a mobile RNA versus the protein having just drifted in by itself," he says. One process that researchers will attempt is catching the RNAs as they become proteins.
For now, however, Westwood is still joyful about the novelty of the finding itself, regardless of the eventual outcome or human applications. "We were very excited when we saw the results. I never expected that we would find so many RNA sequences in the host plant," he says. "We thought ‘maybe we will get published in Science!’"