State Key Laboratory of Plant Genomics, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China.
National Institute of Biological Sciences, Beijing 100101, China.
Plant Cell. 2018 Jul;30(7):1543-1561. doi: 10.1105/tpc.17.00981. Epub 2018 Jun 5.
Plants deploy numerous cell surface-localized pattern-recognition receptors (PRRs) to perceive host- and microbe-derived molecular patterns that are specifically released during infection and activate defense responses. The activation of the mitogen-activated protein kinases MPK3, MPK4, and MPK6 (MPK3/4/6) is a hallmark of immune system activation by all known PRRs and is crucial for establishing disease resistance. The MAP kinase kinase kinase (MAPKKK) MEKK1 controls MPK4 activation, but the MAPKKKs responsible for MPK3/6 activation downstream of diverse PRRs and how the perception of diverse molecular patterns leads to the activation of MAPKKKs remain elusive. Here, we show that two highly related MAPKKKs, MAPKKK3 and MAPKKK5, mediate MPK3/6 activation by at least four PRRs and confer resistance to bacterial and fungal pathogens in The receptor-like cytoplasmic kinases VII (RLCK VII), which act downstream of PRRs, directly phosphorylate MAPKKK5 Ser-599, which is required for pattern-triggered MPK3/6 activation, defense gene expression, and disease resistance. Surprisingly, MPK6 further phosphorylates MAPKKK5 Ser-682 and Ser-692 to enhance MPK3/6 activation and disease resistance, pointing to a positive feedback mechanism. Finally, MEKK1 Ser-603 is phosphorylated by both RLCK VII and MPK4, which is required for pattern-triggered MPK4 activation. These findings illustrate central mechanisms by which multiple PRRs activate MAPK cascades and disease resistance.
植物利用众多细胞表面定位的模式识别受体（PRRs）来感知宿主和微生物衍生的分子模式，这些分子模式在感染过程中特异性释放，并激活防御反应。丝裂原活化蛋白激酶 MPK3、MPK4 和 MPK6（MPK3/4/6）的激活是所有已知 PRR 激活免疫系统的标志，对于建立疾病抗性至关重要。MAP 激酶激酶激酶（MAPKKK）MEKK1 控制 MPK4 的激活，但负责下游不同 PRR 激活 MPK3/6 的 MAPKKK 以及不同分子模式的感知如何导致 MAPKKK 的激活仍不清楚。在这里，我们表明两种高度相关的 MAPKKK，MAPKKK3 和 MAPKKK5，介导至少四种 PRR 的 MPK3/6 激活，并赋予对细菌和真菌病原体的抗性。受体样细胞质激酶 VII（RLCK VII），作为 PRR 的下游，直接磷酸化 MAPKKK5 的 Ser-599，这是模式触发 MPK3/6 激活、防御基因表达和疾病抗性所必需的。令人惊讶的是，MPK6 进一步磷酸化 MAPKKK5 的 Ser-682 和 Ser-692 以增强 MPK3/6 激活和疾病抗性，指出存在正反馈机制。最后，MEKK1 的 Ser-603 被 RLCK VII 和 MPK4 磷酸化，这是模式触发 MPK4 激活所必需的。这些发现说明了多个 PRR 激活 MAPK 级联和疾病抗性的核心机制。
