Genome-Wide Identification and Functional Characterization of CCHC-Type Zinc Finger Genes in Ustilaginoidea virens

Rice false smut caused by Ustilaginoidea virens is a serious disease of rice (Oryza sativa), severely reducing plant mass and yields worldwide. We performed genome-wide analysis of the CCHC-type zinc-finger transcription factor family in this pathogen. We identified and functionally characterized seven UvCCHC genes in U. virens. The deletion of various UvCCHC genes affected the stress responses, vegetative growth, conidiation, and virulence of U. virens. ∆UvCCHC5 mutants infected rice spikelets normally but could not form smut balls. Sugar utilization experiments showed that the ∆UvCCHC5 mutants were defective in the utilization of glucose, sucrose, lactose, stachyose, and trehalose. Deletion of UvCCHC5 did not affect the expression of rice genes associated with grain filling, as revealed by RT-qPCR. We propose that the ∆UvCCHC5 mutants are impaired in transmembrane transport, and the resulting nutrient deficiencies prevent them from using nutrients from rice to form smut balls. RNA-seq data analysis indicated that UvCCHC4 affects the expression of genes involved in mitochondrial biogenesis, ribosomes, transporters, and ribosome biogenesis. These findings improve our understanding of the molecular mechanism underlying smut ball formation in rice by U. virens.