Overexpression of a Mei (Prunus mume) CBF gene confers tolerance to freezing and oxidative stress in Arabidopsis

Mei (Prunus mume Sieb. et Zucc.) is an important ornamental plant in China, but low temperature severely restricts its application in North China. The C-repeat binding factor/Dehydration responsive element binding factors (CBF/DREB1) pathway has important roles in plant responses to cold stress. However, knowledge on the function of CBF/DREB1 genes from Mei and its regulatory roles in freezing and other abiotic stresses is limited. Three PmhCBF genes, designated as PmhCBFa, PmhCBFb and PmhCBFc respectively, were isolated and characterized from Prunus mume ‘Huahudie’. Gene expression analysis revealed that PmhCBFa and PmhCBFb were more induced than PmhCBFc by cold stress, and other stress treatments including H2O2, Mannitol, NaCl and Abscisic Acid also induced the expressions of PmhCBFa/b/c at a relatively lower level. Compared to PmhCBFa and PmhCBFb, PmhCBFc appeared to be more triggered by H2O2 and showed broad regulation potential in all the abiotic stresses. Overexpression of PmhCBFc in Arabidopsis improved freezing and oxidative stress tolerance, and reduced the inhibition of PSII, but delayed development and flowering. The superoxide dismutase (SOD, EC 1.11.1.6) and peroxidase (POD, EC 1.11.1.7) activities were also elevated in the transgenic Arabidopsis plants during freezing-thawing cycles. Our results suggested that PmhCBFc responded to reactive oxygen species (ROS) and functioned in freezing tolerance by enhancing the capacities for ROS scavenging.