Pathogens also can slip through these stomata and begin infecting the plant. However, as Bais's team confirmed, this invasion is halted when the beneficial bacterium Bacillus subtilis is present in the soil where the plant is rooted. The finding was based on tests of approximately 3,000 Arabidopsis plants inoculated with the foliar pathogen Pseudomonas syringae pathovar tomato DC3000 (PstDC3000) during a year-long period.
When a foliar pathogen attacks, as shown in previous research by Bais and his group, the plant recruits Bacillus subtilis to help and facilitates its multiplication. The Bacillus subtilis bacteria bind to the plant's roots and invoke abscisic acid and salicylic acid signaling pathways to close the stomata.
Abscisic acid and salicylic acid are both important hormones involved in plant defense. When a plant encounters adverse environmental conditions, such as drought, for example, abscisic acid triggers the stomata to shut tightly to prevent the plant from dehydrating.
In addition to ramping up plant disease resistance, the use of this rhizobacteria to promote drought tolerance in plants could be a very promising avenue, Bais notes.
"Many bacterial pathogens invade plants primarily through stomata on the leaf surface," Bais says. "But how do plants fight off infection? In our studies of the whole plant, we see this active enlistment by Bacillus subtilis, from root to shoot."
Strikingly, the research team's data revealed that of different root-associated soil bacteria tested, only Bacillus species were effective in closing the stomata and for a prolonged period.
"We know only 1 to 5 percent of what this bug Bacillus subtilis can do, but the potential is exciting," Bais notes, pointing out that there is increasing commercial interest in inoculating crop seeds with beneficial bacteria to reduce pathogen infection. "Just as yo
|Contact: Tracey Bryant|
University of Delaware