GhGAI Interacts with GhAP1 and Regulates Flowering Pathway in Upland Cotton

AP1 is a MADS-Box gene that plays an important role in the flowering pathway of plants. Although GhAP1 has been widely studied, little is known about the proteins that interact with it in cotton. In this study, GhAP1 was used as a bait protein to screen a cDNA library for interacting proteins related to flowering. The results of yeast two-hybrid, bimolecular fluorescence complementation (BiFC) and coimmunoprecipitation (Co-IP) assays showed that GhGAI interacted with GhAP1. The qRTPCR results showed that GhGAI was highly expressed in the flower organs and leaves of upland cotton, and the expression of GhGAI between the early-maturing cultivar and the late-maturing cultivar at the first, second, and fifth leaf stages was significantly different in the shoot apexes. Subcellular localization showed that GhGAI was located in the nucleus. Overexpression of GhGAI in Arabidopsis thaliana could lead to early flowering, increase the contents of GA3 and GA4 hormones, and inhibit the expression of the DELLA proteins AtRGL1 and AtRGL2, while promoting the expression of the flowering core factors AtSOC1, AtLYF, AtFT, and AtAP1. Virus-induced gene silencing (VIGS) of GhGAI in cotton delayed flowering. In silenced plants, the expression of GhRGL1 and GhRGL2 was increased, and the expression of GhSOC1, GhLYF, GhFT, and GhAP1 was decreased. Our results provide important genetic resources for the molecular breeding of early-maturing varieties and lay a foundation for exploring the flowering regulatory network in cotton.