Active DNA Demethylation Mediated by <i>OsGADD45a2</i> Regulates Growth, Development, and Blast (<i>Magnaporthe oryzea</i>) Resistance in Rice

OsGADD45a1, a member of the growth arrest and DNA damage-inducible 45 (GADD45) family in rice, has a newly identified homologue, OsGADD45a2, which differs from OsGADD45a1 in only three amino acids. The role and function of the OsGADD45a2 in DNA demethylation are not well-understood and were investigated in this study. <i>Osgadd45a2</i> mutants exhibited reduced height, shorter panicle length, fewer grains per panicle, and a lower seed setting rate compared with wild-type plants. Moreover, the results showed that <i>OsGADD45a2</i> negatively regulates rice blast fungus resistance and exhibited high expression in various tissues. Using the 3000 Rice Genomes Project database, we identified four major haplotypes (each with over 100 cultivars) based on single-nucleotide polymorphisms in the coding sequence of <i>OsGADD45a2</i>. Among these, Hap4 was associated with a significantly greater plant height than Hap1-3, possibly due to a functional alteration of <i>OsGADD45a2</i> linked to the SNP at position 2614993. In <i>OsGADD45a2</i> overexpression lines, significant decreases in CG and CHG methylation levels were observed in protein-coding genes, leading to their upregulation. Overall, our findings indicate that <i>OsGADD45a2</i> acts as a methylation regulator, mediating the expression of genes essential for plant growth and development and blast resistance.