Magnaporthe oryzae Auxiliary Activity Protein MoAa91 Functions as Chitin-Binding Protein To Induce Appressorium Formation on Artificial Inductive Surfaces and Suppress Plant Immunity

Here, we performed comparative transcriptomic studies of ?Morgs mutant and wild-type strains and found that M. oryzae Aa91 (MoAa91), a homolog of the auxiliary activity family 9 protein (Aa9), was required for surface recognition of M. oryzae. We found that MoAA91 was regulated by the MoMsn2 transcription factor and that its disruption resulted in defects in both appressorium formation on the artificial inductive surface and full virulence of the pathogen. We further showed that MoAa91 was secreted into the apoplast space and was capable of competing with the immune receptor chitin elicitor-binding protein precursor (CEBiP) for chitin binding, thereby suppressing chitin-induced plant immune responses. In summary, we have found that MoAa91 is a novel signaling molecule regulated by RGS and RGS-like proteins and that MoAa91 not only governs appressorium development and virulence but also functions as an effector to suppress host immunity. Overall design: Examination of 4 Dmorgs mutants against wild type Guy11 at 4 time points.

本研究对ΔMorgs突变体与野生型菌株开展比较转录组学研究，发现稻瘟病菌（M. oryzae）Aa91（MoAa91）——辅助活性家族9蛋白（auxiliary activity family 9 protein，Aa9）的同源物——参与稻瘟病菌的表面识别过程。研究证实，MoAA91受MoMsn2转录因子调控，该基因的敲除会导致病原菌在人工诱导表面的附着胞形成缺陷，同时使其完全致病力受损。进一步实验表明，MoAa91可被分泌至质外体空间，并能够与免疫受体几丁质激发子结合蛋白前体（chitin elicitor-binding protein precursor，CEBiP）竞争结合几丁质，从而抑制几丁质诱导的植物免疫反应。综上，本研究发现MoAa91是一类受RGS及RGS样蛋白调控的新型信号分子，其不仅调控附着胞发育与致病力，还可作为效应因子抑制宿主免疫反应。整体实验设计：在4个时间点下，对4株Δmorgs突变体与野生型菌株Guy11开展检测分析。