A gene that helps plants to conserve water has been identified at RIKEN’s Plant Science Center in Yokohama, Japan. The discovery could hold the key to developing drought tolerant crop varieties.

Electron microscope image of a single stoma on the underside of a tomato leaf

Electron microscope image of a single stoma on the underside of a tomato leaf

In order to survive and grow, plants need a constant supply of water. Water is taken up through the plants roots, but is also lost through tiny pores on the leaves called stomata, which plants must open to take in carbon dioxide.

During drought, plants protect themselves from excessive water loss by closely regulating the opening and closing of the stomata. Each pore is flanked by a pair of kidney-shaped guard cells.

When the plant dries out, a plant hormone called abscisic acid signals to these guard cells to change shape, and this closes the stomata. Only when sufficient water is available do the guard cells change back to their original shape, opening the pore and allowing water to pass through once more.

The molecular mechanisms underlying these processes are poorly understood. Takashi Kuromori and his colleagues at RIKEN’s Plant Science Center wanted to understand them better.

Arabidopsis thaliana

Arabidopsis thaliana other wise known as 'thale cress' © Roepers

Working with the model plant Arabidopsis thaliana, they identified a gene called AtABCG22, which is expressed in guard cells and regulates stomatal opening and closing. The gene codes for a protein, which uses chemical energy stored in a biological molecule called Adenosine Triphosphate (ATP) to ferry molecules like abscisic acid across cell membranes.

When water evaporates out of the pores in plant leaves, it has a cooling effect on the leaf. The researchers created mutant plants which didn’t produce the AtABCG22 protein, and used thermal imaging to monitor their water loss. These mutants lost water much more rapidly than normal plants, and were more susceptible to drought stress.

“These findings imply that AtABCG22 plays a role in stomatal regulation and in protecting plants against drought stress,” says Kuromori.

Further experiments, in which the researchers cross bred different mutant plants, revealed that the AtABCG22 gene interacts with other genes involved in metabolism, transport and signalling. “Our next task will be to identify the exact target molecules of AtABCG22,” said Kuromori. “We hope that our work will eventually lead to the breeding of drought tolerant crop varieties.”

For further information contact:

Dr Takashi Kuromori
RIKEN Plant Science Center, Japan
Email: kuromori@psc.riken.jp