The Mitogen-Activated Protein Kinase PlMAPK2 Is Involved in Zoosporogenesis and Pathogenicity of .

As an evolutionarily conserved pathway, mitogen-activated protein kinase (MAPK) cascades function as the key signal transducers that convey information by protein phosphorylation. Here we identified as one of 14 predicted MAPKs encoding genes in the plant pathogenic oomycete . is conserved in and species. We found that was up-regulated in sporangium, zoospore, cyst, cyst germination and early stage of infection. We generated knockout mutants using the CRISPR/Cas9 method. Compared with wild-type strain, the mutants showed no significant difference in vegetative growth, oospore production and sensitivity to various abiotic stresses. However, the sporangium release was severely impaired. We further found that the cleavage of the cytoplasm into uninucleate zoospores was disrupted in the mutants, and this developmental phenotype was accompanied by reduction in the transcription levels of and genes. Meanwhile, the mutants exhibited lower laccase activity and reduced virulence to lychee leaves. Overall, this study identified a MAPK that is critical for zoosporogenesis by regulating the sporangial cleavage and pathogenicity of , likely by regulating laccase activity.