Small Anther, a C2H2-Type Zinc Finger Transcription Repressor, Controls Rice Anther Length Through Regulation of Epidermal Cell Division

Anther length is a crucial agronomic trait that directly correlates with pollen number and pollination efficiency, thereby affecting rice grain yield and hybrid seed production. However, the specific molecular mechanisms regulating rice anther length remain largely unclear. In this study, we identified a short anther (san) mutant generated by CRISPR/Cas9, which exhibited significantly shortened anthers and reduced pollen number, without affecting other agronomic traits or pollen viability. Cytological observations revealed that the shortened anther phenotype in san mutants was caused by reduced epidermal cell number, rather than altered cell size. SAN was highly expressed in spikelets and developing anthers and encodes a nucleus-localized C1-1iG subclass C2H2 zinc finger protein with a conserved QALGGH motif and a C-terminal EAR motif. Further assays demonstrated that SAN functions as a transcriptional repressor, and could interact with the corepressor TPR2 in the nucleus. RNA-seq analysis indicated that SAN influences expression of genes associated with cell cycle and cytokinin, which are critical for epidermal cell division during anther development. Phylogenetic analysis showed that SAN was evolutionarily conserved in plants and was closely related to Arabidopsis SUP/ZFP11 and rice SRO. Collectively, our findings revealed that SAN specifically modulated rice anther length by promoting epidermal cell division and providing new insights into the molecular mechanism of anther size regulation.