The effects of climate change on agriculture usually conjures up an image of plants flailing under drought-stricken skies. But how will agriculture cope with climate change’s other offering—the rise of floods? Increasingly extreme weather worldwide is causing flooding across parts of the planet, and that’s driving a parallel decline in growing area, since most crops can’t subsist in the low-oxygen conditions of waterlogged soil.
But now, researchers writing in PNAS say they have identified a key player in plants’ molecular makeup—one which might help us flood-proof crops against this uncertain future.
In most plants, being submerged in water for prolonged periods leads to hypoxia, a lack of oxygen that shuts down their ability to produce ATP, the molecule that ferries energy around a plant—and which needs air to function. But certain plants like rice, which grows in waterlogged soils, have an unusual capacity to withstand soggy soil for periods of time, because they use a different energy pathway that doesn’t rely on the presence of air.
Researchers know that in these plants, certain genes control that particular energy pathway, and that those genes are regulated by proteins. In turn, the behaviour of those proteins is governed by a unique group of enzymes called plant cysteine oxidases (PCOs)—which, from the top of this chain, set the whole sequence of events in motion.
Because those enzymes are so crucial to helping these plants survive waterlogged soils, the researchers on the new study set out to describe their structure, and illuminate how they work—and how they might therefore be enhanced to improve crops’ adaptations in flooded environments.
By mapping out the detailed structure of the PCOs, the researchers identified key amino acids to target and mutate, which they used as proof that the enzymes could be engineered to behave differently. Then they introduced those engineered enzymes into test thale cress plants—which was practically important, because it proved that these crops could effectively incorporate the altered components. “This is great as it suggests that we can directly translate our biochemical work into a plant context to manipulate PCO function,” says Emily Flashman, a co-author on the new study, and chemist from the University of Oxford, who collaborated on the research with colleague Francesco Licausi.
For now, the enzyme tweaks the researchers have made haven’t resulted in significant changes to plants’ flood control: instead, their primary research aim was proof of principle. But with the structure of the enzymes now fully laid out, they’re in a stronger position to identify targets for mutation. This will enable them to pinpoint the specific amino acids that alter the enzymes’ behaviour in ways that change the downstream activity of proteins and gene regulation—and could ultimately boost flood tolerance.
“We’ll have to use much more subtle changes to the enzyme’s function to produce plants that are usefully flood-tolerant, for example changing how sensitive they are to low-oxygen conditions—think a dimmer switch, rather than an on-off switch,” Flashman says. If they can make the right tweaks, it could help create plants that are able to continue transporting energy and functioning as normal, despite the low-oxygen conditions of their suddenly-aquatic environments. “Really this is where the hard work starts, as we have to understand the enzymes in more detail to be able to achieve that—but we’re on our way!”
Next up, Flashman says, they’re going to investigate precisely how the enzymes interact with oxygen, to point them towards enzyme modifications that will “generate plants with improved flood tolerance, but without any penalty in yield.”
She thinks this early stage discovery, advanced by future insights into enzyme hotspots, could have widespread benefits for crops—including staples like wheat and barley. That’s because PCO enzymes are ‘conserved’ in all crops, she explains, meaning that even though they may not be functional in a plant, their infrastructure still exists within.
So ideally, one day researchers will be able to tap into these reservoir enzymes to breed flood-resilient plants—a potential life raft for our food systems, on our ever-changing planet.
Source: White et. al. “Structures of Arabidopsis thaliana oxygen-sensing plant cysteine oxidases 4 and 5 enable targeted manipulation of their activity.” Proceedings of the National Academy of Sciences. 2020.