| dc.description.abstract | Perception of microbe-associated molecular patterns (MAMPs) by pattern recognition receptors (PRRs) elicits MAMP-triggered immunity (MTI) and contributes to plant resistance to pathogen infection. To understand the mechanisms underlying MTI, we have performed a genetic screen for the Arabidopsis genes governing immune gene expression (AGGIE) using transgenic plants carrying a luciferase reporter under the control of the promoter of a MTI marker gene FRK1(pFRK1::LUC), and identified a dominant mutant aggie5-1 with reduced expression of endogenous MTI marker genes in response to multiple MAMPs and increased susceptibility against bacterial pathogen Pseudomonas syringae. Map-based cloning coupled with bulk sequencing and complementation test revealed that the causative mutation in aggie5-1 occurs on a putative GHSL lipase gene (AGGIE5). AGGIE5 is a plant-specific peroxisome/chloroplast membrane-localized protein and plays a positive role in plant defense against bacterial pathogens. In addition, biochemical and genetic analysis revealed that AGGIE5 contains a NTPase domain with both ATPase and GTPase activities that are indispensable for AGGIE5 function in plant immunity.
A yeast two-hybrid screen identified MPK7, a group C mitogen-activated protein kinase (MPK7) as an AGGIE5 interactor. Importantly, MAMP treatment induces phosphorylation of AGGIE5 at threonine 612 by MPK7, and this phosphorylation is important for AGGIE5 function in plant immunity. CRISPR/Cas9-edited mpk7 knockout mutants showed reduced disease resistance, suggesting a positive role of MPK7 in plant immunity. Significantly, the aggie5-1 mutant AGGIE5^D618N was no longer phosphorylated by MPK7. Together, the data indicate the importance of MPK7-mediated AGGIE5 phosphorylation in plant innate immunity. Oxylipin profiling in WT, aggie5 and mpk7 mutants with and without treatment of a nonpathogenic bacterium which triggers MTI revealed that several oxylipin species, in particular dinor-12-oxo-phytodienoic acid (dn-OPDA), were induced upon elicitation of MTI and were further enhanced in the aggie5 and mpk7 mutants. Importantly, application of dn-OPDA suppressed the expression of some endogenous MTI marker genes and dampened plant defense against bacterial pathogens. Moreover, the dn-OPDA-mediated suppression was OPR3-independent and partially COI1-dependent, suggesting the direct role of dn-OPDA in immunity and indicating dn-OPDA may function as an important signal facilitating fine-tune of defense responses. | en |
