A RACK1 family protein regulates pathogenicity of by acting as a scaffold for MAPK signal modules.

Litchi downy blight caused by is the most destructive disease of litchi (). 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 , 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 , and we found that it was involved in mycelial growth, cell wall integrity, ROS metabolism, laccase activity, and pathogenicity of . PlMAPK1 interacted with RACK1, and they jointly regulated sporangiophore branching of . . Transcriptome analysis showed that . MAPK Phosphatase 1 (PlMKP1) and beta-glucoside (PlBglX) were regulated by PlRACK1, both of which were also required for the pathogenicity of . . 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.