Overexpression of apple MdGAMYB promotes early flowering and increases plant height in transgenic Arabidopsis and tomato

Plant height and flowering ability are key agronomic traits that determine crop productivity. GAMYBs have been reported as gibberellic acid (GA) signaling factors that exhibit essential functions in plant development. In this study, we identified an apple MdGAMYB gene involved in the regulation of flowering and plant height. MdGAMYB is specifically expressed in the buds, flowers, and leaves; its expression levels can be inhibited by exogenous GA3 but induced by paclobutrazol (PAC, a GA synthesis inhibitor). Ectopic overexpression of MdGAMYB promotes early flowering in transgenic Arabidopsis and tomato by upregulating the expression of flowering-promoting genes (e.g., FT, LFY, and FUL). Further analyses indicated that MdGAMYB can directly bind to the apple MdFT1 promoter to upregulate its transcription. In addition, overexpression of MdGAMYB increases the plant height of transgenic tomatoes, which is caused by the modified internode cell length in the stem. MdGAMYB interacts with MdKNATM, which belongs to a class of KNOTTED 1-LIKE HOMEOBOX (KNOX) transcription factors, and MdKNATM inhibits the MdGAMYB-mediated activation of MdFT1 transcription in dual-luciferase reporter system. Taking together, these results showed that the partial functions of MdGAMYB in regulating flowering time and plant height. The data presented herein might provide a new perspective for apple breeding.