Atmospheric CO Alters Resistance of Arabidopsis to by Affecting Abscisic Acid Accumulation and Stomatal Responsiveness to Coronatine.

Atmospheric CO influences plant growth and stomatal aperture. Effects of high or low CO levels on plant disease resistance are less well understood. Here, resistance of against the foliar pathogen pv. DC3000 () was investigated at three different CO levels: high (800 ppm), ambient (450 ppm), and low (150 ppm). Under all conditions tested, infection by resulted in stomatal closure within 1 h after inoculation. However, subsequent stomatal reopening at 4 h, triggered by the virulence factor coronatine (COR), occurred only at ambient and high CO, but not at low CO. Moreover, infection by was reduced at low CO to the same extent as infection by mutant . Under all CO conditions, the ABA mutants and were as resistant to as wild-type plants under low CO, which contained less ABA. Moreover, stomatal reopening mediated by COR was dependent on ABA. Our results suggest that reduced ABA levels at low CO contribute to the observed enhanced resistance to by deregulation of virulence responses. This implies that enhanced ABA levels at increasing CO levels may have a role in weakening plant defense.