Characterization of CBF1, CBF2, CBF3, and CBF4 Genes of Malus Sieversii and Analysis of Their Expression in Different Habitats

Malus sieversii is a cold-resistant rootstock. Um derstanding the mechanisms of its cold resistance is important tor screening cold-resistant gernipiasm sources. CBF genes are closely related to cold resistance in plants. In this study, four CBF genes from M. sieversii, namely MsCBF1, MsCBF2, MsCBF3, and MsCBF4, were cloned and their sequences analyzed. The expression levels of these four MsCBF genes after treatment at a low temperature were compared at different time points and habitats. Our results showed that the four MsCBF proteins have a characteristic CBF protein domain and are water-soluble unstable proteins that are induced by low temperatures. The expression levels of four MsCBF genes were different, and their times of expression levels increased were different too. MsCBF1 was first expressed, followed by MsCBF2, MsCBF3, and MsCBF4. MsCBF1 and MsCBF2 expression levels were lower and MsCBF3 expression was higher after a period of 4 degrees C treatment. Changes in MsCBF expression were consistent. Comprehensive comparison of the four MsCBF gene expression levels in M. sieversii in different habitats indicated that M. sieversii was strongest in Toli county, followed by Emin county, Gongliu county, Huocheng county, and xtnyuan county.