The malectin-like receptor-like kinase LETUM1 modulates NLR protein SUMM2 activation via MEKK2 scaffolding

• Published in: Nature plants Vol. 6; no. 9; pp. 1106 - 1115
• Main Authors: Liu, Jun, Huang, Yanyan, Kong, Liang, Yu, Xiao, Feng, Baomin, Liu, Derui, Zhao, Baoyu, Mendes, Giselle C., Yuan, Peiguo, Ge, Dongdong, Wang, Wen-Ming, Fontes, Elizabeth P. B., Li, Pingwei, Shan, Libo, He, Ping
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.09.2020; Nature Publishing Group
• Subjects: 13; 13/44; 14/19; 14/35; 38/22; 38/90; 631/449/1659; 631/449/1736; 631/449/2169; 631/449/448; 82; 82/1; 82/29; 82/80; 82/83; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Autoimmunity; Biomedical and Life Sciences; Cell surface; Dwarfism; F-box protein; Gene Expression Regulation, Plant; Genes, Plant; Genetic screening; Immune system; Innate immunity; Kinases; Letter; Leucine; Life Sciences; MAP kinase; MAP Kinase Signaling System - genetics; Membrane Proteins - genetics; Membrane Proteins - metabolism; Mutation; Nlr protein; Nucleotides; Pattern recognition; Pattern recognition receptors; Phenotypes; Plant Immunity - genetics; Plant Sciences; Proteins; Receptors; RNA-mediated interference; Scaffolding; Signal transduction; Signaling; Suppressors; Ubiquitination; United States > US; Texas; China
• ISSN: 2055-0278; 2055-0278
• DOI: 10.1038/s41477-020-0748-6

The innate immune system detects pathogen-derived molecules via specialized immune receptors to prevent infections 1 – 3 . Plant immune receptors include cell surface-resident pattern recognition receptors (PRRs, including receptor-like kinases (RLKs)), and intracellular nucleotide-binding domain leucine-rich repeat proteins (NLRs). It remains enigmatic how RLK- and NLR-mediated signalling are connected. Disruption of an immune-activated MEKK1–MKK1/2–MPK4 MAPK cascade activates the NLR SUMM2 via the MAPK kinase kinase MEKK2, leading to autoimmunity 4 – 9 . To gain insights into the mechanisms underlying SUMM2 activation, we used an RNA interference-based genetic screen for mekk1 autoimmune suppressors and identified an uncharacterized malectin-like RLK, named LETUM1 (LET1), as a specific regulator of mekk1–mkk1/2 – mpk4 autoimmunity via complexing with both SUMM2 and MEKK2. MEKK2 scaffolds LET1 and SUMM2 for protein stability and association, and counter-regulates the F-box protein CPR1-mediated SUMM2 ubiquitination and degradation, thereby regulating SUMM2 accumulation and activation. Our study indicates that malectin-like RLK LET1 senses the perturbance of cellular homoeostasis caused by the deficiency in immune-activated signalling and activates the NLR SUMM2-mediated autoimmunity via MEKK2 scaffolding. Plants with loss of function mutations in the MEKK1–MKK1/2–MPK4 MAP kinase pathway show strong autoimmunity phenotypes and dwarfism. Through a suppressor genetic screen, the malectin-like receptor kinase LET1 is identified as a new regulator of immune signalling.