Functional Divergence of AP1 and FUL Genes Related to Flowering Regulation in Upland Cotton

Abstract The AP1/FUL transcription factors are important for floral development, but the underlying molecular mechanisms remain unclear. In this study, we cloned and identified two AP1/FUL-like genes, GhAP1.1 and GhFUL2, in upland cotton, which is a commonly cultivated economically valuable crop. Sequence alignments and phylogenetic analyses indicated GhAP1.1 and GhFUL2, which are encoded by genes in the AP1/FUL clade, have conserved N-terminals, but diverse C-terminal domains. A quantitative real-time PCR analysis revealed that GhAP1.1 and GhFUL2 were expressed in the flower and root, and had the opposite expression patterns during different shoot apical meristem stages. The upregulated expression of GhAP1.1 in Arabidopsis and the silencing of GhAP1.1 did not induce significant changes to the flowering time or floral organs, but the transcript levels of the florigen FT gene and the AP1 homolog GhMADS42 increased. The overexpression of GhFUL2 in Arabidopsis delayed flowering and promoted bolting by decreasing the FT and LFY expression levels. Silencing GhFUL2 in cotton dramatically increased the expression of GhFT and GhMADS42 and promoted flowering. Additionally, yeast two-hybrid and bimolecular fluorescence complementation assays indicated that GhAP1.1 can interact with the SVP homolog GhSVP1, whereas GhFUL2 can form heterodimers with SEP1, SEP4 homologs, and GhSVP1. Therefore, we proved that the functional divergence of GhAP1.1 and GhFUL2, which involved changes in sequences and expression patterns, influenced the regulation of cotton flower development.