Abstract: The anthracnose caused by Colletotrichum gloeosporioides poses a significant threat to the global mango (Mangifera indica L.) fruit industry. Although histone deacetylases (HDACs) are well recognized to be involved in plant immunity, the role of HDAC-mediated nonhistone deacetylation in the fruit immune response remains elusive. In the present study, MiHDA3, an HDAC from the RPD3/HDA1 subfamily, was identified as a candidate for regulating mango resistance based on the greatest induction of MiHDA3 in response to infection of C. gloeosporioides among the 19 tested HDAC genes. Transient overexpression of MiHDA3 in mango fruit strengthened the disease resistance by enhancing the activities of defense-related enzymes (phenylalanine ammonia-lyase (PAL) and β-1,3-glucanase (GLU)) and upregulating the expression levels of MiPAL and MiGLU. These increases occurred concomitantly with increased accumulation of local H₂O₂, a critical signaling molecule. The opposite effects on resistance and H₂O₂ production were observed in MiHDA3-silenced mango fruit. Physiological assays revealed that exogenous H₂O₂ treatment suppressed anthracnose development in mango fruit after inoculation with C. gloeosporioides, whereas treatment with diphenylene iodonium, an inhibitor of endogenous H₂O₂ generation, exacerbated disease symptoms. Furthermore, the mango catalase 1 (MiCAT1), a redox homeostasis-related protein, was confirmed to negatively regulate the resistance of mango fruit to C. gloeosporioides by catalyzing the decomposition of H₂O₂. Mechanistic investigations revealed that MiHDA3-mediated deacetylation of MiCAT1 at lysine residues K227 and K233 reduced the enzymatic activity and protein stability of MiCAT1, contributing to enhanced resistance in mango fruit. Collectively, these findings highlight that the functional interplay between HDACs and catalases can modulate the immune response in post-harvest fruits, and reveal a novel mechanism by which HDACs enhance mango disease resistance through the deacetylation of nonhistone proteins and the regulation of their biochemical functions.

Key words: catalase, histone deacetylase, immune response, mango anthracnose, nonhistone deacetylation