An atypical R2R3 <scp>MYB</scp> transcription factor increases cold hardiness by <scp>CBF</scp>‐dependent and <scp>CBF</scp>‐independent pathways in apple

Abstract

Summary Apple ( Malus × domestica ) trees are vulnerable to freezing temperatures. However, there has been only limited success in developing cold‐hardy cultivars. This lack of progress is due at least partly to lack of understanding of the molecular mechanisms of freezing tolerance in apple. In this study, we evaluated the potential roles for two R2R3 MYB transcription factors ( TF s), MYB 88 and the paralogous FLP ( MYB 124), in cold stress in apple and Arabidopsis . We found that MYB 88 and MYB 124 positively regulate freezing tolerance and cold‐responsive gene expression in both apple and Arabidopsis . Chromatin‐Immunoprecipitation‐ qPCR and electrophoretic mobility shift assays showed that Md MYB 88/Md MYB 124 act as direct regulators of the COLD SHOCK DOMAIN PROTEIN 3 ( Md CSP 3 ) and CIRCADIAN CLOCK ASSOCIATED 1 ( Md CCA 1 ) genes. Dual luciferase reporter assay indicated that Md CCA 1 but not Md CSP 3 activated the expression of Md CBF 3 under cold stress. Moreover, Md MYB 88 and Md MYB 124 promoted anthocyanin accumulation and H 2 O 2 detoxification in response to cold. Taken together, our results suggest that Md MYB 88 and Md MYB 124 positively regulate cold hardiness and cold‐responsive gene expression under cold stress by C‐ REPEAT BINDING FACTOR ( CBF )‐dependent and CBF ‐independent pathways.