The basal transcription factor II H subunit Tfb5 is required for stress response and pathogenicity in the tangerine pathotype ofAlternaria alternata

The basal transcription factor II H (TFIIH) is a multicomponent complex. In the present study, we characterized a TFIIH subunit Tfb5 by analysing loss- and gain-of-function mutants to gain a better understanding of the molecular mechanisms underlying stress resistance and pathogenicity in the citrus fungal pathogenAlternaria alternata. Tfb5 deficiency mutants (Delta Aatfb5) decreased sporulation and pigmentation, and were impaired in the maintenance of colony surface hydrophobicity and cell wall integrity. Delta Aatfb5increased sensitivity to ultraviolet light, DNA-damaging agents, and oxidants. The expression ofAatfb5was up-regulated in the wild type upon infection in citrus leaves, implicating the requirement ofAatfb5in fungal pathogenesis. Biochemical and virulence assays revealed that Delta Aatfb5was defective in toxin production and cellwall-degrading enzymes, and failed to induce necrotic lesions on detached citrus leaves.Aatfb5fused with green fluorescent protein (GFP) was localized in the cytoplasm and nucleus and physically interacted with another subunit, Tfb2, based on yeast two-hybrid and co-immunoprecipitation analyses. Transcriptome and Antibiotics & Secondary Metabolite Analysis Shell (antiSMASH) analyses revealed the positive and negative roles ofAatfb5in the production of various secondary metabolites and in the regulation of many metabolic and biosynthetic processes inA. alternata. Aatfb5may play a negative role in oxidative phosphorylation and a positive role in peroxisome biosynthesis. Two cutinase-coding genes (AaCut2andAaCut15) required for full virulence were down-regulated in Delta Aatfb5. Overall, this study expands our understanding of howA. alternatauses the basal transcription factor to deal with stress and achieve successful infection in the plant host.