The Arabidopsis leucine rich repeat receptor-like kinase MIK2 interacts with RKS1 and participates to the control of quantitative disease resistance to the bacterial pathogen Xanthomonas campestris

Molecular mechanisms underlying qualitative resistance have been intensively studied. In contrast, although quantitative disease resistance (QDR) is a common, durable and broad-spectrum form of immune responses in plants, only a few related functional analyses have been reported. In this context, the atypical kinase RKS1 is a major actor of QDR to the bacterial pathogen Xanthomonas campestris (Xcc) and is positioned in a robust protein-protein decentralized network. Among the putative interactors of RKS1 found by yeast two hybrid screening, we identified the receptor like kinase MDIS1-Interacting Receptor-like Kinase 2 (MIK2). Here, by multiple and complementary strategies including protein-protein interaction tests, mutant analysis and network reconstruction, we report that MIK2 is a component of RKS1 mediated QDR to Xcc. First, by co-localization experiment, co-immunoprecipitation (Co-IP) and Bimolecular Fluorescence Complementation (BiFC), we validated the physical interaction between RKS1 and MIK2 in the plasma membrane. Using mik2 mutants, we then showed that MIK2 is required for QDR at the same level as RKS1. Interestingly, a catalytic mutant of MIK2 was able to interact with RKS1 but unable to fully complement the mik2-1 mutant in response to Xcc. Finally, we investigated a potential role of the MIK2-RKS1 complex as a scaffolding component for coordination of perception events, by constructing a RKS1-MIK2 centered protein-protein network. Eight mutants corresponding to seven RLKs of this network showed a strong and significant alteration in QDR to Xcc. Our findings provide new insights into the molecular mechanisms underlying perception events involved in QDR to Xcc.