Fine mapping and functional validation reveal two incomplete dominant genes controlling photoperiod-sensitive flowering in Gossypium hirsutum.

The genes GhAGL8 and GhJAZ1, which regulate flowering time in upland cotton were mapped to chromosomes D03 and D08 using a late-flowering (photoperiod-sensitive) semi-wild landrace as the parent in an F mapping population. Fine mapping and functional validation identified them as candidate genes. Photoperiod-sensitive flowering in Gossypium hirsutum is closely linked to the node position of the first fruiting branch (NFFB). Utilizing an F₂ population generated from a cross between the late-flowering semi-wild cotton Palmeri 37 and the modern cultivar CCRI74, we mapped two genes related to NFFB with additive effects on chromosome D03 (1.13 cM) and D08 (2.72 cM). Through fine mapping and sequence analysis, we identified AGAMOUS-LIKE8(GhAGL8) and JASMONATE ZIM-DOMAIN1(GhJAZ1) as candidate genes. Subcellular localization assays indicated that both proteins are predominantly localized in the nucleus. GhAGL8 exhibited consistently higher expression levels in CCRI 74 compared to Palmeri 37, across various leaf stages. Virus-induced gene silencing (VIGS) of GhAGL8 delayed NFFB and increased plant height. A haplotype variation in the promoter region of GhAGL8 (TT/- at -1036 bp) was strongly correlated with variations in NFFB and gene expression. GhJAZ1 was more highly expressed in CCRI74 than in Palmeri 37, particularly in leaves, stems, and calyces, with expression progressively increasing during seedling development. A CCRI74-specific amino acid insertion in GhJAZ1 may enhance flower bud differentiation, promoting early flowering. This research identifies two novel genes (GhAGL8 and GhJAZ1) as key regulators of cotton flowering time and highlights Palmeri 37 as a valuable germplasm resource for dissecting photoperiod adaptation mechanisms in cotton.