Transcriptome Analysis and Functional Validation Identify a Putative bZIP Transcription Factor, Fpkapc, that Regulates Development, Stress Responses, and Virulence in Fusarium pseudograminearum

Fusarium pseudograminearum is a soilborne, hemibiotrophic phytopathogenic fungus that causes Fusarium crown rot and Fusarium head blight in wheat. The basic leucine zipper proteins (bZIPs) are evolutionarily conserved transcription factors that play crucial roles in a range of growth and developmental processes and the responses to biotic and abiotic stresses. However, the roles of bZIP transcription factors remains unknown in F. pseudograminearum. In this study, a bZIP transcription factor Fpkapc was identified to localize to the nucleus in F. pseudograminearum. A mutant strain (Δfpkapc) was constructed to determine the role of Fpkapc in growth and pathogenicity of F. pseudograminearum. Transcriptomic analyses revealed that many genes involved in basic metabolism and oxidation-reduction processes were downregulated, whereas many genes involved in metal iron binding were upregulated in the Δfpkapc strain, compared with the wild type (WT). Correspondingly, the mutant had severe growth defects and displayed abnormal hyphal tips. Conidiation in the Fpkapc mutant was reduced, with more conidia in smaller size and fewer septa than in the WT. Also, relative to WT, the Δfpkapc strain showed greater tolerance to ion stress, but decreased tolerance to H₂O₂. The mutant caused smaller disease lesions on wheat and barley plants, but significantly increased TRI gene expression, compared with the WT. In summary, Fpkapc plays multiple roles in governing growth, development, stress responses, and virulence in F. pseudograminearum.