Chemical Holds Water

Representation of synthetic opabactin showing two binding locations (yellow dotted lines)

Sean Cutler, UC Riverside

The pores, or stomata, in plant leaves allow the gas exchange necessary for both photosynthesis and respiration. Open stomata also allow water to escape, which can be detrimental in times of drought. Researchers have developed a powerful new agrochemical that mimics a natural hormone, abscisic acid (ABA), which shrinks the size of stomata and allows plants to better retain water.

An earlier ABA-mimic called, “quinabactin,” had been developed in 2013 by Sean Cutler, a plant cell biology professor at the University of California Riverside, and his research team. That chemical was only moderately effective at boosting plant drought tolerance because it only bonded with one of two handle-like structures in the relevant plant hormone receptor, whereas ABA more securely attaches to both handles.

To find a better alternative that could bind with both hormone receptors, the team combed through a database of millions of hormone-mimicking molecules, searching for promising candidates. They identified a potential precursor and used X-ray crystallography to image its structure deeply. The process revealed regions where some structural tweaks could render the molecule more effective. The researchers dubbed the resulting fine-tuned chemical, “opabactin,” or OP for short. (The name pays homage to slang used by video game players for “overpowered,” meaning a dominant weapon or character.)

Wheat plants under drought stress without (left) and with opbactin treatment (right)

Sean Cutler, UC Riverside

OP has demonstrated seven times the receptor-bonding strength of naturally produced ABA, and plants treated with OP show increased water retention within hours of application. This rapid responsiveness means farmers can deploy the chemical when urgently needed—a useful attribute because the tradeoff for improved water retention is slowed growth—instead of pre-emptively treating crops well in advance of unpredictable weather. OP was also effective in boosting the drought tolerance of wheat and tomatoes, two plants that quinabactin could not help. Before ever reaching farmer’s fields, however, OP will have to undergo significantly more development, as well as safety testing for regulatory approval. (Science)