Cloning and characterization of CaGID1s and CaGAI in Capsicum annuum L.

Fruit set and development are affected by many phytohormones, including gibberellin. Little is known regarding molecular mechanism underlying gibberellin mediated fruit set and development especially in Capsicum. Three gibberellin receptors, CaGID1b.1, CaGID1b.2 and CaGID1c, and a DELLA protein, CaGAI, have been identified in Capsicum annuum L. During the fruit development, the expression level of CaGID1c was low, and the expression fold change is mild. However, CaGID1b.1 and CaGID1b.2 were relatively higher and more acute, which indicates that CaGID1b.1 and CaGID1b.2 may play an important role in fruit pericarp, placenta and seed. Ectopic expressions of CaGID1b.1, CaGID1b.2 and CaGID1c in Arabidopsis double mutant gid1a gid1c increased plant height, among which CaGID1b.2 had the most significant effect; CaGAI reduced plant height in double mutant rga-24/gai-t6, having a similar function to AtGID1 and AtGAI in stem elongation. Yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays indicated that CaGID1b.1 and CaGID1b.2 interact with CaGAI in a GA-dependent manner, while CaGID1c interacts with CaGAI in a GA-independent manner. Our study reveals the key elements during gibberellin signaling in Capsicum and supports the critical importance of gibberellin for Capsicum fruit set and development.