An Acer palmatum R2R3-MYB Gene, ApMYB77, Confers Freezing and Drought Tolerance in Arabidopsis thaliana

Low temperature is one of the most prominent environmental factors affecting plant growth. As a deciduous arboreal tree, Acer palmatum has considerable ornamental and economic value; however, the molecular mechanisms underlying cold stress regulation in this species have yet to be determined. In this study, we performed Illumina high-throughput sequencing of 18 libraries obtained from A. palmatum subjected to cold treatment and subsequently identified a differentially expressed R2R3-MYB family gene, ApMYB77, which was then cloned and functionally characterized. The expression of ApMYB77 was induced by cold and drought treatments, and overexpression in A. thaliana enhanced the freezing tolerance (- 9 degrees C for 6 h) of transgenic plants compared with that of wild-type plants. The survival rates of transgenic plants (89% and 92%) were significantly higher than the wild-type plants (52%). Moreover, the transcript abundances of CBF-dependent regulatory pathway genes (AtCBF1, AtCBF2, AtCBF3, AtCBF4, AtCOR6.6A, AtCOR15B, AtCOR78, AtCOR414, and AtKIN1) were found to be significantly up-regulated in the transgenic lines. Enhanced abscisic acid (ABA)-dependent drought tolerance in transgenic plants was a further consequence of the overexpression of ApMYB77 following treatment of 15% polyethylene glycol for 4 d, compared with that in wild-type plants. In contrast, the expressions of genes (AtANAC072, AtDREB2A, AtERD1, AtMYB2, AtRD20, and AtRD29A) positively regulated by ABA were activated. Overall, the findings of this study indicate that ApMYB77 confers both freezing and drought tolerances.