| Summary: | Histone deacetylases (HDACs) are vital epigenetic modifiers not only in regulating plant development but also in abiotic- and biotic-stress responses. Though to date, the functions of HD2C—an HD2-type HDAC—In plant development and abiotic stress have been intensively explored, its function in biotic stress remains unknown. In this study, we have identified HD2C as an interaction partner of the <i>Cauliflower mosaic virus</i> (CaMV) P6 protein. It functions as a positive regulator in defending against CaMV infection. The <i>hd2c</i> mutants show enhanced susceptibility to CaMV infection. In support, the accumulation of viral DNA, viral transcripts, and the deposition of histone acetylation on the viral minichromosomes are increased in <i>hd2c</i> mutants. P6 interferes with the interaction between HD2C and HDA6, and P6 overexpression lines have similar phenotypes with <i>hd2c</i> mutants. In further investigations, P6 overexpression lines, together with CaMV infection plants, are more sensitive to ABA and NaCl with a concomitant increasing expression of ABA/NaCl-regulated genes. Moreover, the global levels of histone acetylation are increased in P6 overexpression lines and CaMV infection plants. Collectively, our results suggest that P6 dysfunctions histone deacetylase HD2C by physical interaction to promote CaMV infection.
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