A Malectin-Like Receptor Kinase Regulates Cell Death and Pattern-Triggered Immunity in Soybean

Plant cells can sense conserved molecular patterns through pattern-recognition receptors (PRRs) and initiate pattern-triggered immunity (PTI). Details of the PTI signaling network are starting to be uncovered in Arabidopsis, but are still poorly understood in other species, including soybean (Glycine max). In this study, we perform a forward genetic screen for autoimmunity-related lesion mimic mutants (lmms) in soybean and identify two allelic mutants, which carry mutations in Glyma.13G054400, encoding a malectin-like receptor kinase (RK). The mutants exhibit enhanced resistance to both bacterial and oomycete pathogens, as well as elevated ROS production upon treatment with the bacterial pattern flg22. Overexpression of GmLMM1 gene in Nicotiana benthamiana severely suppresses flg22-triggered ROS production and oomycete pattern XEG1-induced cell death. We further show that GmLMM1 interacts with the flg22 receptor FLS2 and its co-receptor BAK1 to negatively regulate flg22-induced complex formation between them. Our study identifies an important component in PTI regulation, and reveals that GmLMM1 acts as a molecular switch to control an appropriate immune activation, which may also be adapted to other PRR-mediated immune signaling in soybean.

植物细胞可通过模式识别受体（pattern-recognition receptors, PRRs）识别保守的分子模式，并启动模式触发免疫（pattern-triggered immunity, PTI）。目前，拟南芥中的PTI信号网络细节已逐步被解析，但在包括大豆（Glycine max）在内的其他物种中，相关调控机制仍有待深入阐释。本研究针对大豆中的自身免疫相关类病斑突变体（autoimmunity-related lesion mimic mutants, lmms）开展正向遗传筛选，鉴定到两个等位突变体，其突变位点位于Glyma.13G054400基因，该基因编码类凝集素样受体激酶（malectin-like receptor kinase, RK）。该突变体对细菌及卵菌病原菌均表现出增强的抗性，且在经细菌模式分子flg22处理后，活性氧（reactive oxygen species, ROS）爆发水平显著升高。本研究在本氏烟（Nicotiana benthamiana）中过表达GmLMM1基因，可严重抑制flg22诱导的ROS爆发以及卵菌模式分子XEG1引发的细胞死亡。我们进一步证实，GmLMM1可与flg22受体FLS2及其共受体BAK1相互作用，负调控flg22诱导的二者之间复合物的形成。本研究鉴定出PTI调控通路中的关键组分，并揭示GmLMM1可作为分子开关，控制适度的免疫激活，该调控机制或也可适用于大豆中其他PRR介导的免疫信号通路。