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

Abstract

ORCID IDs: 0000-0003-0202-3890 (C.L.); 0000-0002-9943-2975 (J.-M.Z.) Stomata are natural openings through which many pathogenic bacteria enter plants. Successful bacterial pathogens have evolved various virulence factors to promote stomatal opening. Here, we show that the Pseudomonas syringae type III effector protein AvrB induces stomatal opening and enhances bacterial virulence in a manner dependent on RPM1-INTERACTING4 (RIN4), which promotes stomatal opening by positively regulating the Arabidopsis plasma membrane H + -ATPase (AHA1), which is presumed to directly regulate guard cell turgor pressure. In support of a role of AHA1 in AvrBinduced stomatal opening, AvrB enhances ATPase activity in plants. Unexpectedly, AHA1 promotes the interaction between the jasmonate (JA) receptor CORONATINE INSENSITIVE1 (COI1) and JASMONATE ZIM-DOMAIN (JAZ) proteins and enhances JA signaling. JA signaling is required for optimum stomatal infection in AHA1-active plants. Similarly, AvrB also induces the COI1-JAZ9 interaction and the degradation of multiple JAZ proteins. AvrB-induced stomatal opening and virulence require the canonical JA signaling pathway, which involves the COI1 and NAC transcription factors. The findings thus point to a previously unknown pathway exploited by P. syringae that acts upstream of COI1 to regulate JA signaling and stomatal opening.

Direct and Indirect Visualization of Bacterial Effector Delivery into Diverse Plant Cell Types during Infection

“…Thus, guard cells can be directly targeted by pathogen effectors to promote colonization. Consistent with this finding, AvrB has been demonstrated to promote bacterial growth and stomatal opening upon surface inoculation (Zhou et al, 2015). Collectively, these data indicate that effectors can be directly delivered into cells of the leaf surface in order to enhance entry into the leaf interior and suppress defense responses.…”

“…Mean and SD values were calculated from scores of >7 plants. Zhou et al, 2015). Here, we demonstrated that AvrB and AvrPtoB can be directly delivered into guard cells, which flank stomatal pores, upon surface inoculation using the GFP strand system.…”

Extracellular ATP Acts on Jasmonate Signaling to Reinforce Plant Defense

“…A similar observation was reported by Zhou et al (2015), in which protein degradation of JAZs was promoted by RIN4 or AHA1 in transient coexpression assays in tobacco without addition of COR or JA-Ile. It is conceivable that this event is mediated by endogenous JA, given that there is a certain level of JAs, e.g.…”

Stomatal Defense a Decade Later

“…This may potentially generate an unknown signal that promotes the interaction between COI1 and JAZ proteins to degrade JAZ and enhance JA signaling. In addition, AvrB induces MYC-mediated expression of ANAC019, ANAC055, and ANAC072 genes in Arabidopsis and the tomato NAC homolog JASMONIC ACID2-LIKE gene to repress SA responses (Du et al, 2014;Zhou et al, 2015;Gimenez-Ibanez et al, 2017). Therewith, like COR, AvrB appears to regulate stomatal opening through manipulating the SA-JA antagonism.…”

“…For example, COR requires RPM1-INTERACTING4 (RIN4), a negative regulator of plant innate immunity, to open the stomatal pore as evidenced by the facts that neither Pst DC3000 nor COR was able to reopen stomata of rpm1/ rps2/rin4 mutants (Liu et al, 2009;Zhou et al, 2015;Lee et al, 2015). The perception of flg22 via the FLS2 receptor leads to phosphorylation of the plasma membrane H + -ATPases and subsequent alkalization of the apoplast, which, along with the induction of ROS via NADPH oxidase RbohD, triggers stomatal closure (Liu et al, 2009;Li et al, 2014).…”