The bZIP transcription factor UvbZIP6 mediates fungal growth, stress response, and false smut formation in Ustilaginoidea virens

Abstract

Rice false smut, caused by Ustilaginoidea virens, is one of the most destructive diseases in major world rice-producing regions. Basic leucine zipper (bZIP) proteins, which belong to an evolutionarily conserved transcription factor family and play critical roles in various biological processes in eukaryotes, have been previously identified in U. virens; however, their functions still need to be further elucidated. Therefore, we aimed to analyze the biological roles of UvbZIP6, a member of the bZIP family in U. virens. In this study, we found that UvbZIP6 was highly up-regulated at 7 days post-inoculation. Deletion of UvbZIP6 in U. virens resulted in an increase in fungal growth and sensitivity to Congo red and calcofluor white, whereas a decrease in sensitivity to hyperosmotic, oxidative, and sodium dodecyl sulfate stresses. Conidiation capacity was reduced in UvbZIP6-knockout mutants, but conidial morphology and germination were not affected. Although UvbZIP6-knockout mutants caused infection in rice plants, they could not form false smut balls. Our study indicates that UvbZIP6 is required for fungal growth, conidiation, stress response, and false smut ball formation of U. virens.