SlCOL1 and SlCOL2 play dual roles in photoperiodic flowering and inflorescence architecture in tomato

Abstract Photoperiodic flowering in plants integrates environmental cues with endogenous signaling pathways where CONSTANS (CO) family genes serve as central regulators of seasonal adaptation. While extensively studied in model species, the molecular mechanisms underlying CO-mediated photoperiodic regulation in tomato remain largely unexplored. In this study, through systematic functional characterization of three tomato CO-like genes (SlCOL1/2/3), we established that SlCOL1 and SlCOL2 function as long-day-specific floral repressors by directly binding to and activating the flowering inhibitor SELF-PRUNING 5G (SP5G). Beyond flowering control, we uncovered a role for SlCOL1/2 in shaping inflorescence architecture through the transcriptional activation of APETALA2 (AP2) family genes in meristematic tissues. Our findings reveal a dual regulatory paradigm where SlCOL1/2 coordinate photoperiod-dependent flowering timing via SP5G signaling while simultaneously governing inflorescence complexity through AP2-mediated meristem programming. These results provide mechanistic insights into both the conserved photoperiodic regulatory mechanisms inherited from ancestral CO functions and lineage-specific innovations driving reproductive adaptation in Solanaceae. The elucidated SlCOL1/2-SP5G/AP2 module advances our understanding of photoperiodic adaptation while offering strategic targets for optimizing flowering time and inflorescence structure in tomato breeding.