MpMYBS3 as a crucial transcription factor of cold signaling confers the cold tolerance of banana

Banana (Musa spp.) is an important tropical crops. Low temperature is one of the key environmental stresses, which greatly affects the global banana production. Different varieties of banana exhibit a high degree of genetic variability for cold tolerance. Compared with Cavendish banana, Dajiao has superior cold tolerance. Cloning of Dajiao cold-tolerant genes and characterization of their functions could reveal the molecular mechanism of cold tolerance in Dajiao. Our previous comparative transcriptome analysis of cold-sensitive Cavendish banana and cold-tolerant Dajiao identified several cold-tolerance candidate genes in Dajiao. In this study, a Dajiao candidate gene, MpMYBS3 (homolog of MYBS3 in rice), encoding a transcription factor, was cloned and characterized. Amino acid sequence alignments showed that MpMYBS3 belongs to the R1-type MYB transcription factors. Subcellular localization analysis indicated that MpMYBS3 is located in the nucleus. Heterologous overexpression of MpMYBS3 in banana showed that the transgenic lines had significantly higher cold tolerance than the wild-type, which might be associated with the increased accumulation of proline, and a reduction in malondialdehyde content and electrolyte leakage. Surprisingly, MYBS3 repressed the well-known ICE1-CBF-dependent cold signaling pathway in banana: the MaCBF1 and MaCBF2 genes were repressed at the transcriptional level after cold treatment. However, MaMKRY46 was significantly induced in transgenic bananas overexpressing MpMYBS3 under cold stress. These findings suggest that MYBS3-mediated cold signaling as a key player in cold adaptation of banana.