MdGRF11, a growth-regulating factor, participates in the regulation of flowering time and interacts with MdTFL1/MdFT1 in apple

GROWTH-REGULATING FACTORs (GRFs) are plant-specific transcription factors that play important roles in regulating plant growth, development, and tolerance to stresses. However, there has been no in-depth research on the GRF genes and their roles in apple. A total of sixteen GRF genes were identified in the apple genome (GDDH13 V1.1), that expressed differentially in various tissues, in which the highest expression levels were observed particularly in shoot tips and apical buds. Among MdGRFs, the MdGRF11 was cloned and further investigated. Overexpression of the MdGRF11 in Arabidopsis plants promoted flowering, root elongation and leaf size. Further investigation indicated that MdGRF11 interacts with key flower genes FLOWERING LOCUS T (FT) and TERMINAL FLOWER1 (TFL1). The transient assays demonstrated that MdGRF11 represses the expression of knotted-like homeobox (MdKNOX19). Furthermore, MdTFL1 can compete with MdFT1 for complex formation with MdGRF11 to regulate the expression of MdKNOX19. Taken together, our results suggest that MdGRF11 protein is involved in fine-tuning of the floral transition possibly through interaction with the MdFT1 and MdTFL1 proteins.