Stomata and drought tolerance

 

Plants engineered for on-demand drought tolerance

Tolerance can be induced using a chemical already approved for agriculture.

by Timmer J. (2015)

in Ars Technica 2015-02

Excerpt

The signaling network that was used normally responds to a chemical made by plants called abscisic acid. Its response triggers longterm changes by regulating the activity of genes. But it also has a short-term effect: it helps plants hold on to water. It does this by affecting what are called “guard cells,” which form part of the openings (called stomata) that plants use to regulate the flow of gases into and out of their leaves.

When stomata are fully open, critical gases like the carbon dioxide required for photosynthesis can enter the leaves while the oxygen produced by it can exit. Unfortunately for plants, water vapor that forms in the open interior spaces of a leaf can also escape through these same stomata. Abscisic acid causes guard cells to close off the stomata. While this process will slow down photosynthesis, it also lets the plants hold on to much more water, allowing them to better tolerate a period of going without.

Plants sense abscisic acid through a variety of receptors that latch on to this molecule, so the researchers picked one of these and tried to get it to latch on to something different. First they disabled a key piece of the protein that interacts with abscisic acid. Next, they targeted lots of mutations to the parts of the receptor that form a binding pocket for this molecule. Once the binding pocket was altered, they tested whether the protein stuck to any one of a panel of 15 different chemicals, all of which are already used in agriculture.

While they had several promising chemical-receptor combinations, they focused on those that latched on to a chemical (called mandipropamid), which is used in agriculture to kill fungi that attack plants. An abscisic acid receptor with three mutations bound weakly to the fungicide, and the team of scientists subjected this receptor to further mutations, selecting for enhanced binding; five additional mutations (one each in five different tests) were identified this way. So the authors engineered a receptor with both the original three mutations and all five of the new ones.

The resulting receptor had a very strong affinity for the fungicide, so they put it back into plants, using a small relative of mustard called Arabidopsis to do their initial tests.

Read the full article: Ars Technica