MdbHLH93, an apple activator regulating leaf senescence, is regulated by ABA and MdBT2 in antagonistic ways

Summary The molecular mechanism of leaf senescence in apple ( Malus domestica ) is still not fully understood. We used gene expression analysis and protein–protein interactions to decipher the relationships of abscisic acid ( ABA ) and two proteins, Mdb HLH 93 and Md BT 2, in the senescence process. We found that Mdb HLH 93 promoted leaf senescence and the expression of senescence‐related genes, which exhibited similar effects to ABA on leaf senescence. Mdb HLH 93 activated directly the transcription of Md SAG 18 . We also found that an ABA ‐responsive protein, Md BT 2, interacted directly with Mdb HLH 93, and induced the ubiquitination and degradation of the Mdb HLH 93 protein, and thus delayed leaf senescence. Our findings provide new insights into the regulatory network of leaf senescence through the functional interactions among ABA , Mdb HLH 93 and Md BT 2.