Pseudomonas syringae Effector Protein AvrB Perturbs Arabidopsis Hormone Signaling by Activating MAP Kinase 4

Abstract

SUMMARY Pathogenic microbes often modulate phytohormone physiology in the host to their advantage. We previously showed that the Pseudomonas syringae effector protein AvrB perturbs hormone signaling exemplified by an up-regulation of jasmonic acid (JA) response gene expression and enhances plant susceptibility. Here we show that AvrB does so by interacting with the Arabidopsis mitogen activated protein kinase MAP KINASE 4 (MPK4) and HSP90 chaperone components. AvrB induces MPK4 activation and this is directly promoted by the HSP90 chaperone. A previously identified AvrB-interacting protein, RIN4, also is required for AvrB to perturb hormone signaling and induce plant susceptibility, likely by acting down-stream of MPK4. These findings uncover a novel pathway through which a bacterial effector protein stimulates host processes to the benefit of the P. syringae bacterium.

An Arabidopsis Plasma Membrane Proton ATPase Modulates JA Signaling and Is Exploited by the Pseudomonas syringae Effector Protein AvrB for Stomatal Invasion

“…This is consistent with our previous findings that bacterially delivered AvrB can substitute for COR function to enhance JA response gene expression (He et al, 2004;Cui et al, 2010).…”

“…The avrB T125A and avrB R266G mutants are nonfunctional in triggering RPM1 resistance and JA signaling (Ong and Innes, 2006;Cui et al, 2010). We examined if these mutants were affected in their ability to open stomata of rpm1 epidermal strips when delivered by Pst cor -.…”

“…The abundance of all six tested JAZ-HA proteins was greatly reduced in the presence of AvrB-FLAG ( Figure 6A), suggesting that AvrB induces the degradation of multiple JAZ proteins. The expression of AvrB R266G and AvrB T125A mutants, which are unable to induce JA signaling (Cui et al, 2010), failed to induce JAZ9-HA degradation ( Figure 6B), indicating that the AvrB-induced JAZ protein degradation correlated with its ability to activate JA signaling.…”

“…We previously showed that AvrB can complement COR deficiency and induce JA response genes in plants in a RIN4-dependent manner (He et al, 2004;Cui et al, 2010). We sought to test if RIN4 was similarly required for avrB-induced stomatal virulence.…”

“…The AvrB-RIN4 interaction has been hypothesized to promote bacterial virulence in plants lacking RPM1 (Dangl and Jones, 2001;Kim et al, 2005), but direct evidence is lacking. Nonetheless, we have previously shown that AvrB can substitute COR to induce JA response gene expression in a manner dependent on COI1 and RIN4 (He et al, 2004;Shang et al, 2006;Cui et al, 2010). Whether the elevated JA signaling contributes to bacterial virulence remains unknown.…”