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Engineering plants to withstand drought and tolerate salinity

A genetic tweak gives cress plants the qualities of succulents, a trait that researchers are now looking to expand into other crops
July 3, 2020

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Researchers have managed to engineer plants with bigger cells that can store more water—getting them to behave like water-harboring succulents that thrive in deserts around the world. What’s more, this trait could be widely transferred to agricultural crops, a new study finds.

The discovery, detailed in The Plant Journal, hinges on a gene that’s found in wine grapes, called VvCEB1, which causes the cells of the fruit to enlarge during development. When the researchers bred that gene into thale cress—a plant widely used as an experimental model in research—they were able to over-express it, which led the plants to develop unusually large cells, capable of storing larger quantities of water. The plants could not only withstand extremely dry conditions, but were also able to tolerate higher salinity in the soil, the researchers found.

In fact, when exposed to drought-like conditions in the experiment, they showed that only 16 to 25% of the regular thale cress plants—which lacked the over-expressed VvCEB1 gene—ultimately survived. The difference in the engineered plants was striking: between 91 and 94% of them survived the dire conditions and continued to grow. 

Compared to the non-engineered control plants, the engineered cress were found to retain much more water—and the pace at which they lost water was also  notably slower than in the controls, the experiments showed.

Presumably, some of this was thanks to their new, larger cells, which act efficiently like a reservoir in times of need. But the researchers discovered that as well as larger cells, the VvCEB1-expressing plants also had fewer and smaller stomata on their leaves. Especially under dry conditions, water transpires out of stomata at a rapid pace—so having fewer and smaller portals to the outside world helps them to keep more water locked in. 

On top of all this, the engineered thale cress plants had another advantage over their regular counterparts: equipped with larger cells, these plants became more salt-tolerant, the experiments showed. That’s likely because bigger, more watery cells would help the plant dilute salt that’s absorbed from saline soils, as the researchers explain. And what’s more, the engineered cress had larger leaves and produced more seeds than the control—suggesting that productivity isn’t sacrificed by this particular genetic tweak.

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Interestingly, the researchers made this discovery while pursuing a different research goal. They’d been trying to engineer plants to contain a trait known as ‘crassulacean acid metabolism’ (CAM), a naturally-occurring feature in some plants that helps them conserve more water by photosynthesizing only at night—when it’s cooler and safer for stomata to be open. To enable this trait, the researchers needed to engineer plants that contained what they call the right ‘leaf anatomy’: namely, larger cells in which to store an ingredient called malic acid, which plays a crucial role in enabling the unusual photosynthetic response. It just so happens that the larger cell sizes which serve that purposes could double up as storage space for water, too.

Altogether, the researchers’ efforts resulted in the model of a plant that could potentially be drought-tolerant and more adaptable in the higher-salinity landscapes that are expected to expand under climate change. “Water-storing tissue is considered among the most successful adaptations to drought in the plant kingdom,” the researchers write. And yet, it’s been largely unexplored as a way to bolster crops against the effects of climate change, they add.

They aim to change that: next up, they’ll be combining their discoveries on CAM and reservoir cells, and trying to engineer them jointly into crops.  

Source: Lim et. al. “Plant tissue succulence engineering improves water‐use efficiency, water‐deficit stress attenuation and salinity tolerance in Arabidopsis.” The Plant Journal. 2020.
Image: PxFuel

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