Mitogen-activated protein kinase phosphatase 1 (MKP1) negatively regulates Microbe-Associated Molecular Pattern-triggered immunity in Arabidopsis

Abstract

In the search for early signalling components of Microbe-Associated Molecular Pattern (MAMP)-triggered immunity we identified a null allele of the mitogen-activated protein kinase phosphatase 1 gene (MKP1). MKP1 functions as a negative regulator of broad MAMP-triggering immunity responses since mkp1 mutant is more resistant to the necrotrophic fungus Plectosphaerella cucumerina BMM (PcBMM), the hemibiotrophic bacterium Pseudomonas syringae pv. tomato DC3000 and the biotrophic oomycete Hyaloperonospora arbidopsidis. MKP1 regulates ROS production by modulating the NADPH oxidase RBOHD, since mkp1 plants constitutively overexpressing RbohD (35S::RbohD mkp1) display elevated ROS levels upon MAMP treatment. In addition, a metabolomic analysis revealsa significant reprograming of the metabolic profile in mkp1, with more than 200 metabolites showing differential accumulation compared to wild-type plants. Antimicrobial compounds of the glucosinolate pathway or camalexin as well as defense-associated metabolites, like salicylic acid, are among the compounds that mkp1 plants accumulate at high levels. To characterize the elements responsible for this broad enhanced resistance, we crossed mkp1 mutant to lines compromised in the production of tryptophan derived metabolites and salicylic acid. Patho-tests performed in the combinatory mutants reveal that different defensive elements are required for the mkp1 enhanced resistance to P. cucumerinaBMM and P. syringae pv. tomato DC3000, suggesting that MKP1 down-regulates distinct defensive pathways in response to different pathogens.