Exploration In The Relationship Between Cdc42 And Chm1 In Magnaporthe Grisea

As one of the most important members of Rho-family proteins (also called Rho GTPases), Cdc42 plays a key role in fungal development, polarity growth and pathogenicity. PAK kinases, which play as downstream effectors of Rho GTPases such as Cdc42 and Rac, have been implicated in various aspects of cytoskeletal reorganization. The rice blast fungus, Magnaporthe grisea, is taken as a model for the study of filamentous fungi. Its infection process involves a complex cell morphogenesis in response to host defense mechanism. We expected that signal transmittion between MgCdc42 and the member of PAK kinases, Chm1 (or Mst20) , is involved in regulation of this complex process. In this study, we had a clear understanding about the relationship between Cdc42 and Chm1．Through RT-PCR analysis, we found that MgCdc42 functioned at the upstream of Chml. And Chm1 physically interacted with MgCdc42 via its PBD domain in yeast two-hybrid assays. Furthermore, we separately transformed the PBD domain deletion of Chm1 gene into wild-type strain, MgCdc42 deletion mutant and Chm1 deletion mutant. While expressing PBD domain deletion of Chm1 in wild-type strain Guy11 was not essential for development and pathogenicity in M.grisea, deletion of the PBD domain in Chm1 gene fully restored conidial morphology of MgCdc42 deletion mutant. But these conidia did not develop appressoria normally. Moreover, deletion of the PBD domain in Chm1 gene fully restored almost every defect of Chm1 deletion mutant, such as conidiation, conidial and mycelial morphology, despite pathogenic decline. These data suggested that MgCdc42 and Chm1 have a close functional relativity in M.grisea. MgCdc42-Chm1 signal pathway plays a key role in the morphogenesis of conidi and fungal polarity growth. And Chm1 is not the only downstream effector for MgCdc42．MgCdc42 may recruit other pathways to modulate various stages of development in M. grisea.