Maize CONSTANS-like gene ZmCOL13 promotes flowering time under short-day conditions in Arabidopsis

Although CONSTANS-like (COL) genes are essential for photoperiodic flowering in plants, their functional diversification in maize (Zea mays) remains unclear. A systematic analysis of the COL family demonstrated that ZmCOL13 exhibits peak expression in mature leaves. Cis-element analysis of its promoter predicted regulation by light, hormones, and stress cues. ZmCOL13 was found to be phylogenetically closely related to AtCOL3-5, OsCOL4, and ZmCOL3. ZmCOL13 encodes a 364-amino acid protein that contains BBOX, B-box1-BBX-like, and CCT domains and was localized to the nucleus, which is consistent with its identity as a plant transcription factor. Heterologous overexpression of ZmCOL13 in Arabidopsis resulted in accelerated flowering by 12-13 days under short-day conditions but showed no significant difference under long-day conditions compared to the wild type (Col-0). Transcriptome analysis identified 1313 differentially expressed genes, and Gene Ontology analysis revealed that two biological process terms associated with photoperiod were significantly enriched. Overexpression of ZmCOL13 increased AtFT expression by several hundred-fold, which may represent a primary mechanism underlying ZmCOL13-induced increases in flowering in Arabidopsis. Based on co-expression and phylogenetic analyses in maize, we developed a model in which ZmCOL13 was predicted to modulate flowering time by partially regulating the expression of Arabidopsis flowering gene AtFT orthologs (ZmZCN7, ZmZCN8, and ZmZCN12).