MoMtg1 Acts as a Novel Transcriptional Repressor of MoSwi6 During Appressorium-Mediated Penetration in the Rice Blast Fungus.

Appressoria are specialized penetration structures for many plant pathogenic fungi, including the rice blast fungus Magnaporthe oryzae, which evolves a set of complicated regulatory mechanisms to control appressorium development and function. Cell cycle control is essential for appressorium-mediated penetration, but the mechanism underlying its role remains largely elusive. Here, a conserved protein MoMtg1 is identified in filamentous fungi as a novel transcriptional repressor that plays a crucial role in cell cycle regulation. MoMtg1 directly interacts with transcription factor MoSwi6 and inhibits its transcriptional activity. Deletion of MoMtg1 or MoSwi6 results in cell cycle defects during appressorium development. Both mutants are abnormal in melanization, appressorium turgor generation, reactive oxygen species (ROS) accumulation, and septin assembly. MoSwi6 positively and MoMtg1 negatively regulate the expression of MoCYC1, the cyclin gene essential for maintaining normal appressorium development. Overexpression of MoCYC1 in the wild type resulted in similar defects in appressorium development and function with ∆Momtg1 and ∆Moswi6 mutants. It is also shown that silencing MoMTG1 with the host-induced gene silencing strategy conferred resistance against M. oryzae in transgenic plants. Furthermore, a small molecule is identified as a MoMtg1-inhibitor by protein modelling and shows to inhibit MoMtg1 functions and reduce M. oryzae infection. Overall, the study reports a novel cell cycle regulator and its underlying mechanisms during appressorium-mediated penetration, which has great potentials as a target for disease control.