OsBBX19 encoding a CCT domain-containing protein controls heading date in rice

Heading date is a pivotal agronomic trait that governs regional adaptation and grain yield in rice (Oryza sativa L.). The CCT domain‑containing protein OsBBX19 (also known as OsCCT22) has been previously identified as a heading‑date regulator. In this study, we further report the molecular functional characterization of OsBBX19. Overexpression of OsBBX19 delayed heading under both short-day conditions (SDs) and long-day conditions (LDs). GUS staining and RT-qPCR analyses revealed that OsBBX19 was constitutively expressed across various organs, and that its overexpression significantly suppressed the expression of Hd3a, RFT1, and Ehd1 while increasing Ghd7 expression, suggesting that OsBBX19 is associated with the Ghd7-Ehd1-Hd3a/RFT1 flowering pathway. We also demonstrated that OsBBX19 physically interacts with CONSTANS-like protein interacting protein 1 (CPIP1). Haplotype analysis revealed significant indica-japonica differentiation of OsBBX19, and the frequency of Hap3 and Hap5 increased during the improvement process of indica rice. Collectively, our results provide additional insights into the molecular mechanism by which OsBBX19 regulates heading date in rice, offering potential genetic resources for breeding optimization.

The online version contains supplementary material available at 10.1007/s11032-026-01681-6.