Perception and First Defense Responses Against Pseudomonas syringae pv. phaseolicola in Phaseolus vulgaris : Identification of Wall-Associated Kinase Receptors

Common bean ( ) is attacked by several pathogens such as the biotrophic gamma-proteobacterium pv. . To study the pv. -bean interaction during the first stages of infection, leaf discs of a susceptible bean cultivar Riñón were infected with pathogenic pv. . Using this experimental system, we tested six new putative wall-associated kinase (WAK) receptors, previously identified in silico. These six WAKs (PvWAKs) showed high protein sequence homology to the well-described WAK1 (AtWAK1) receptor and, by phylogenetic analysis, clustered together with AtWAKs. The expression of 1 increased at very early stages after the pv. infection. Time course experiments were performed to evaluate the accumulation of apoplastic H O , Ca influx, total H O , antioxidant enzymatic activities, lipid peroxidation, and the concentrations of abscisic acid and salicylic acid (SA), as well as the expression of six defense-related genes: , , , , , and . The results showed that overexpression of occurred 2 h after pv. infection without a concomitant increase in SA levels. Although apoplastic H O increased after infection, the oxidative burst was neither intense nor rapid, and an efficient antioxidant response did not occur, suggesting that the observed cellular damage was caused by the initial increase in total H O early after infection. In conclusion, Riñón can perceive the presence of pv. , but this recognition results in only a modest and slow activation of host defenses, leading to high susceptibility to pv. .