A novel leucine-rich repeat receptor-like kinase MRK1 regulates resistance to multiple stresses in tomato

Leucine-rich repeat receptor-like kinases (LRR-RLKs) are ubiquitous in higher plants, which act as receptors of extracellular signals to trigger multiple physiological processes. However, the functions of the majority of LRR-RLKs remain largely unknown, especially in tomato (Solanum lycopersicum L.). Here, we found that MRK1 (Multiple resistance-associated kinase 1), encoding a novel tomato LRR-RLK, was significantly induced either by temperature stresses or bacterial pathogen attacks. Knocking out MRK1 impaired the tolerance to both cold and heat stress, accompanied with the decrease in transcripts of master regulators C-repeat binding factor 1 (CBF1) and Heat shock transcription factor a-1a (HsfA1a), respectively. Additionally, mrk1 mutants were hypersensitive to Pseudomonas syringae pv. tomato DC3000 and Ralstonia solanacearum and compromised pattern-triggered immunity (PTI) responses as evidenced by decreased reactive oxygen species production and reduced upregulation of the PTI marker genes. Moreover, bimolecular fluorescence complementation, split-luciferase assay and coimmunoprecipitation supported the existence of complex formation between the MRK1, FLS2 and Somatic embryogenesis receptor kinase (SERK3A/SERK3B) in a ligand-independent manner. This work demonstrates that tomato MRK1 as a novel positive regulator of multiple stresses, which might be a potential breeding target to improve crop stress resistance.