A Sirtuin Protein FocSir2 Is Important for Oxidative Adaptation and Virulence of Banana Fusarium Wilt

Banana Fusarium wilt, caused by Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4), is a devastating disease of banana, but the molecular mechanism underlying its pathogenesis remains to be elucidated. In this study, we identified a sirtuin family protein, FocSir2, in Foc TR4. Global protein acetylation level was significantly increased in FocSIR2 knockout mutants compared with the wild type (WT), suggesting that FocSir2 is likely a deacetylase. FocSir2 was localized in the cytoplasm and was relatively highly expressed in conidia and during early infection. Deletion of FocSIR2 resulted in compact mycelial growth and a significant reduction in microconidium production, indicating a role for FocSIR2 in the asexual development of Foc TR4. The plate stress experiment indicates that FocSir2 plays important roles in cell wall integrity, osmotic stress, and pH stress responses. Notably, deletion of FocSIR2 led to greatly attenuated virulence toward banana corms and leaves, indicating that FocSir2 is essential for full virulence of Foc TR4. GO and KEGG analyses of differentially expressed genes from RNA-seq revealed enrichment in reactive oxygen species (ROS) metabolism and the TCA cycle. RT-qPCR confirmed that the expression of all eight ROS detoxification-related genes was reduced. The FocSIR2 knockout mutant was highly sensitive to H2O2 and exhibited an ROS burst during banana infection, indicating that FocSir2 is involved in the oxidative stress adaptation of Foc TR4 to the host. Further experiments demonstrated that deletion of FocSIR2 significantly decreased the activities of the TCA cycle key enzymes malate dehydrogenase and α-ketoglutarate dehydrogenase, as well as the content of acetyl-CoA. Yeast library screening and yeast two-hybrid assays identified three proteins, FocRlc1, FOIG_08568, and FocFstf1, that interact with FocSir2, and their acetylation levels were significantly increased in the FocSIR2 knockout mutant, indicating that these three proteins are targets of FocSir2. Collectively, this study demonstrates that the deacetylase FocSir2 plays important roles in the asexual development and environmental stress responses of the pathogen and participates in the pathogenesis of the banana Fusarium wilt pathogen by regulating oxidative stress adaptation to the host.