A RACK1 family protein regulates pathogenicity of <i>Peronophythora litchii</i> by acting as a scaffold for MAPK signal modules

Litchi downy blight caused by <i>Peronophythora litchii</i> is the most destructive disease of litchi (<i>Litchi chinensis</i>). RACK1 (Receptor for activated C kinase 1) is a group of scaffold proteins, mainly involved in the regulation of various signaling pathways by interacting with signal transduction proteins and affecting the activity of these proteins. In this study, a RACK1 homologue identified in <i>P. litchii</i>, and named PlRACK1. The protein was found to interact with the mitogen-activated protein kinases, PlMAPK1 and PlMAPK2. CRISPR/Cas9-mediated genome editing technology was used to knock out <i>PlRACK1</i>, and we found that it was involved in mycelial growth, cell wall integrity, ROS metabolism, laccase activity, and pathogenicity of <i>P. litchii</i>. PlMAPK1 interacted with RACK1, and they jointly regulated sporangiophore branching of <i>P</i>. <i>litchii</i>. Transcriptome analysis showed that <i>P</i>. <i>litchii</i> MAPK Phosphatase 1 (PlMKP1) and beta-glucoside (PlBglX) were regulated by PlRACK1, both of which were also required for the pathogenicity of <i>P</i>. <i>litchii</i>. As well, PlMKP1 also interacted with PlMAPK1 and PlMAPK2. These results provide insights into the direct interactions between RACK1, MAPKs, and MKP, and their functions in growth, development, and pathogenesis in a plant pathogenic oomycete. PlRACK1 played a critical role in response to ROS and pathogenesis of <i>P</i>. <i>litchii</i>.PlMAPK1 interacted with PlRACK1, and they jointly regulated sporangiophore branching.PlMKP1 interacted with PlMAPK1/PlMAPK2 and was involved in pathogenesis.PlBglX, identified by transcriptome analysis of PlRACK1 mutant, is a virulence factor. PlRACK1 played a critical role in response to ROS and pathogenesis of <i>P</i>. <i>litchii</i>. PlMAPK1 interacted with PlRACK1, and they jointly regulated sporangiophore branching. PlMKP1 interacted with PlMAPK1/PlMAPK2 and was involved in pathogenesis. PlBglX, identified by transcriptome analysis of PlRACK1 mutant, is a virulence factor.由荔枝霜疫霉（Peronophythora litchii）引起的荔枝霜疫霉病是荔枝（Litchi chinensis）最具破坏性的病害。RACK1（激活的C激酶1受体，Receptor for activated C kinase 1）是一类支架蛋白，主要通过与信号转导蛋白相互作用并调控其活性，参与多种信号通路的调控。本研究在荔枝霜疫霉中鉴定到一个RACK1同源蛋白，命名为PlRACK1。研究发现该蛋白可与丝裂原活化蛋白激酶PlMAPK1和PlMAPK2相互作用。我们采用CRISPR/Cas9介导的基因组编辑技术敲除PlRACK1，结果显示其参与荔枝霜疫霉的菌丝生长、细胞壁完整性、活性氧（Reactive Oxygen Species，ROS）代谢、漆酶活性以及致病性调控。PlMAPK1可与RACK1相互作用，二者共同调控荔枝霜疫霉的孢囊梗分枝。转录组分析显示，荔枝霜疫霉的MAPK磷酸酶1（PlMKP1）与β-葡萄糖苷（PlBglX）均受PlRACK1调控，且二者均为荔枝霜疫霉致病性所必需。此外，PlMKP1还可与PlMAPK1和PlMAPK2相互作用。本研究结果揭示了RACK1、MAPKs与MKP之间的直接相互作用，以及它们在植物病原卵菌的生长发育与致病过程中的功能。PlRACK1在荔枝霜疫霉响应活性氧及致病过程中发挥关键作用。PlMAPK1与PlRACK1相互作用，二者共同调控孢囊梗分枝。PlMKP1可与PlMAPK1/PlMAPK2相互作用并参与致病过程。PlBglX通过对PlRACK1突变体的转录组分析鉴定得到，是一种毒力因子。PlRACK1在荔枝霜疫霉响应活性氧及致病过程中发挥关键作用。PlMAPK1与PlRACK1相互作用，二者共同调控孢囊梗分枝。PlMKP1可与PlMAPK1/PlMAPK2相互作用并参与致病过程。PlBglX通过对PlRACK1突变体的转录组分析鉴定得到，是一种毒力因子。