MdKNOX15, a class I knotted-like transcription factor of apple, controls flowering and plant height by regulating GA levels through promoting the MdGA2ox7 transcription

•MdKNOX15 overexpression resulted in delayed flowering and reduced plant height in Arabidopsis.•MdKNOX15 overexpression resulted in growth inhibition of apple calli.•MdKNOX15 bind to and activate the MdGA2ox7 gene, which contributes to GA inactivation.•Both the N-and C-terminal domain of MdKNOX15 interact with MdBLH.