Integrated cytological, transcriptomic, and functional analyses implicate GhFUL and GhAP1-D3 in flowering and boll opening in upland cotton (Gossypium hirsutum L.)

The timing of cotton boll opening is an important component of early-maturity performance in upland cotton ( Gossypium hirsutum L.). However, the molecular mechanisms underlying boll opening remain poorly understood. The early-maturing cultivar Yuzhishi84–1 (Yu) and the late-maturing cultivar Ganmian12 (Gan), which differ significantly in boll-opening time, were used as experimental materials. Integrated cytological and transcriptomic analyses identified GhFUL as a candidate gene associated with boll opening. VIGS-mediated suppression of GhFUL delayed flowering and boll opening and prolonged the flower-boll stage. At 10 days post-anthesis (DPA), GhFUL -silenced bolls showed altered dorsal-suture histology and a significantly different invagination angle. Yeast two-hybrid (Y2H), luciferase complementation imaging (LCI), and coimmunoprecipitation (Co-IP) assays demonstrated a physical interaction between GhFUL and GhAP1-D3. Genetic interaction analysis suggested that GhFUL and GhAP1-D3 might act in the same or overlapping pathway during flowering and boll opening. These findings support the involvement of GhFUL and GhAP1-D3 in flowering and boll-opening regulation and provide a basis for future functional studies.