Data_Sheet_1_Functional Diversification Analysis of Soybean Malectin/Malectin-Like Domain-Containing Receptor-Like Kinases in Immunity by Transient Expression Assays.docx

Plants have responded to microbial pathogens by evolving a two-tiered immune system, involving pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) and effector-triggered immunity (ETI). Malectin/malectin-like domain-containing receptor-like kinases (MRLKs) have been reported to participate in many biological functions in plant including immunity and resistance. However, little is known regarding the role of MRLKs in soybean immunity. This is a crucial question to address because soybean is an important source of oil and plant proteins, and its production is threatened by various pathogens. Here, we systematically identified 72 Glycine max MRLKs (GmMRLKs) and demonstrated that many of them are transcriptionally induced or suppressed in response to infection with microbial pathogens. Next, we successfully cloned 60 GmMRLKs and subsequently characterized their roles in plant immunity by transiently expressing them in Nicotiana benthamiana, a model plant widely used to study host-pathogen interactions. Specifically, we examined the effect of GmMRLKs on PTI responses and noticed that a number of GmMRLKs negatively regulated the reactive oxygen species burst induced by flg22 and chitin, and cell death triggered by XEG1 and INF1. We also analyzed the microbial effectors AvrB- and XopQ-induced hypersensitivity response and identified several GmMRLKs that suppressed ETI activation. We further showed that GmMRLKs regulate immunity probably by coupling to the immune receptor complexes. Furthermore, transient expression of several selected GmMRLKs in soybean hairy roots conferred reduced resistance to soybean pathogen Phytophthora sojae. In summary, we revealed the common and specific roles of GmMRLKs in soybean immunity and identified a number of GmMRLKs as candidate susceptible genes that may be useful for improving soybean resistance.

植物已通过演化形成双层免疫系统以应对微生物病原，该系统包含病原相关分子模式（pathogen-associated molecular pattern, PAMP）触发的免疫（PTI）与效应因子触发的免疫（ETI）。已有研究表明，含凝集素/类凝集素结构域的类受体激酶（Malectin/malectin-like domain-containing receptor-like kinases, MRLKs）参与植物的诸多生物学过程，包括免疫与抗病反应。然而，目前对于MRLKs在大豆免疫中的功能尚不清楚，这是一个亟待解决的关键科学问题：大豆是重要的油脂与植物蛋白来源，但其生产受到多种病原微生物的威胁。本研究系统鉴定了72个大豆（Glycine max）MRLKs（GmMRLKs），并发现其中多数基因在微生物病原侵染后出现转录水平的上调或下调。随后，本研究成功克隆了60个GmMRLKs，并通过在广泛用于宿主-病原互作研究的模式植物本氏烟草（Nicotiana benthamiana）中瞬时表达这些基因，解析了它们在植物免疫中的功能。具体而言，我们检测了GmMRLKs对PTI反应的影响，发现多个GmMRLKs可负调控flg22与几丁质诱导的活性氧爆发，以及XEG1和INF1触发的细胞死亡。我们还分析了微生物效应因子AvrB与XopQ诱导的过敏反应，鉴定出数个可抑制ETI激活的GmMRLKs。本研究进一步证实，GmMRLKs可能通过与免疫受体复合物结合来调控免疫反应。此外，在大豆毛状根中瞬时过表达数个筛选得到的GmMRLKs，可降低植株对大豆疫霉（Phytophthora sojae）的抗性。综上，本研究阐明了GmMRLKs在大豆免疫中的共性与特异性功能，并鉴定出数个可作为候选感病基因的GmMRLKs，有望用于大豆抗病性改良。