The BELL1-like homeobox gene MdBLH14 from apple controls flowering and plant height via repression of MdGA20ox3

Apple growth and yield are largely dependent on plant height and flowering characteristics. The BELL1-like homeobox (BLH) transcription factors regulate extensive plant biological processes. However, the BLH-mediated regulation of plant height and flowering in apple remains elusive. In the current study, 19 members of the MdBLH family were identified in the apple genome. Segmental duplication and purifying selection are the main reasons for the evolution of the MdBLH genes. A BLH1-like gene, MdBLH14, was isolated and functionally characterized. The MdBLH14 was preferentially expressed in flower buds, and downregulated during the floral induction period. The subcellular localization in tobacco leaves indicated that MdBLH14 is a nuclear protein. Overexpression of MdBLH14 in Arabidopsis led to a significant dwarfing and late-flowering phenotype by hindering active GA accumulation. Additionally, MdKNOX19, another member of the TALE superfamily, physically interacts with MdBLH14 and synergistically inhibits the expression of MdGA20ox3. This is the first report on the function of the MdBLH14 from apple, and its mechanism involving plant flower induction and growth. The data presented here provide a theoretical basis for genetically breeding new apple varieties.