Physiological and TMT-labeled proteomic analyses reveal important roles of sugar and secondary metabolism in Citrus junos under cold stress.

Citrus junos is a widely used citrus grafting rootstock in china because of its excellent tolerance to cold stress. However, the physiological and molecular mechanisms underlying this process remain unknown. In this study, physiological and tandem mass tag-based proteomic analyses were performed to elucidate the mechanism of the Citrus junos response to cold stress. Physiological data showed that severe cold stress decreased photosynthetic parameters and caused cell membrane damage and membrane lipid peroxidation in Citrus junos leaves compared to the control. A total of 6, 678 distinct proteins species were identified, and 413 proteins species were significantly differentially accumulated in the leaves of Citrus junos seedling after cold stress. Bioinformatics analysis revealed that the differentially abundance protein species mainly related to the starch and sucrose metabolism, secondary metabolites biosynthesis and phenylpropanoid biosynthesis in the leaves of Citrus junos seedling after cold stress. Further physiological assays showed that the contents of soluble starch, fructose, glucose and phenols were significantly increased in Citrus junos leaves after cold stress. Collectively, our data reveals that sugar and secondary metabolism could play important roles in Citrus junos in response to cold stress.