A team of researchers has identified for the first time a group of plant proteins that "shut the door" on bacteria that would otherwise infect the plant's leaves.
The researchers in Denmark, at the University of California, Davis, and at UC (University of California) Berkeley, have done the study that provides a better understanding of plants' immune systems and will likely find application in better protecting agricultural crops and horticultural plants against diseases.
"The ability of a plant's immune system to recognize disease-causing microorganisms is critical to the plant's survival and productivity," said Gitta Coaker, a UC Davis plant pathologist and lead author on the study.
She noted that, over the last 20 years, scientists have identified a number of proteins that are important for regulating the plant immune system.
"Our ability to purify an immune protein complex will serve as a starting point to understand how these proteins signal in the plant," Coaker said.
"A greater understanding of how these proteins function is fundamental knowledge that can be applied to prevent plant disease," Coaker added.
In studying the RIN4 protein, Coaker and her colleagues identified six previously uncharacterized proteins that can associate with RIN4 inside plant cells.
One protein, called AHA1, was characterized in-depth and found to be key to the immune response in Arabidopsis plants.
AHA1 can act to regulate the opening and closing of tiny holes called stomata, found on the underside of the leaf.
The stomata allow gases and water to pass in and out of the leaf. This is the same opening that allows bacteria and other invading microbes to gain entrance to the plant.
The stomata are each flanked by two guard cells, which control these vitally important portals to the leaf.
When the guard cells swell, the stomata close. Conversely, when the water content of the guard cells decreases, the stomata open.
The six proteins identified in this study were found to be intricately involved with the biochemical processes that enable the plant to recognize and block out invading bacteria.
The researchers found that RIN4 can act to regulate AHA1 and that both proteins work together to control stomatal openings in response to a disease-causing microorganism.
"These findings highlight how important regulation of the stomata is in Arabidopsis immunity," Coaker said.