Calcineurin-dependent transcription factor CRZ1, an important pathogenicity factor in Ustilaginoidea virens, directly regulates ustilaginoidin biosynthesis

Ustilaginoidea virens , the causal agent of rice false smut, produces a variety of mycotoxins, including ustilaginoidins, which are highly toxic and harmful to humans and animals. The Ugs gene cluster has been identified to be responsible for ustilaginoidin biosynthesis in U. virens . However, little is yet known about how ustilaginoidin biosynthetic genes are transcriptionally regulated in U. virens . In this study, we reveal that the transcription factor calcineurin-responsive zinc finger 1 (CRZ1) is a major regulator of ustilaginoidin biosynthesis in U . virens . Notably, a novel calcineurin-dependent response element (CDRE) has been identified for CRZ1 in U. virens and is enriched in the promoters of ustilaginoidin synthesis genes, including Pks1 and UgsH . Electrophoretic mobility shift assay and chromatin immunoprecipitation-PCR analysis demonstrated that UvCRZ1 activates the expression of Pks1 and UgsH through directly binding CDREs in their promoters. We further find that UvCRZ1 is important for vegetative growth, conidiogenesis, conidial development, virulence, and mycotoxin biosynthesis in U. virens . Consistently, transcriptome analysis revealed that UvCRZ1 positively regulates the expression of genes involved in pathogenesis, secondary metabolism, and energy metabolism. These findings deepen the understanding of the regulatory mechanisms underlying virulence and mycotoxin biosynthesis, particularly ustilaginoidin production, in phytopathogenic fungi.