OsSDG715, a Histone H3K9 Methyltransferase, Integrates Auxin and Cytokinin Signaling to Regulate Callus Formation in Rice

Efficient callus induction is essential for the genetic transformation of rice (Oryza sativa), yet its regulatory mechanisms remain elusive. Previously, through a genome-wide association study (GWAS), we identified a significant associated locus on chromosome 8. In this study, we characterized this locus and demonstrated that OsSDG715, encoding a histone H3K9 methyltransferase, is the causal gene that positively regulates callus formation in rice. Results revealed that OsSDG715 is highly expressed during callus induction and exhibits natural variations associated with callus induction rate (CIR). Knockout of OsSDG715 via CRISPR/Cas9 led to a significant decrease in CIR and impaired callus morphology, indicating its positive regulation of callus formation. RNA-seq analyses revealed that 326 and 705 differentially expressed genes (DEGs) were upregulated and downregulated in sdg715 mutants, including auxin-responsive genes (OsIAA14, OsYUCCA6), cytokinin-related genes (OsCKX4, ARR10), and stress-responsive factors. Further analysis showed reduced endogenous indole-3-acetic acid (IAA) levels and increased zeatin levels in sdg715 mutants. These findings advance our understanding of the molecular mechanisms underlying rice callus formation, and offering valuable insights for optimizing tissue culture in molecular breeding.