iTRAQ-Based Quantitative Proteome Analysis Insights into Cold Stress of Winter Turnip Rapa (Brassica rapa L.) Grown in the Field

Abstract Winter Turnip rapa (Brassica rapa L.) is a major oilseed crop in Northern China, where its production was severely affected by chilling and freezing stress. Previous studies have demonstrated that differentially accumulated proteins (DAPs) were expressed in roots and leaves under control chilling stress. In this study, the isobaric tag for relative and absolute quantification (iTRAQ) technology was performed to identify DAPs under freezing stress. Two winter rapaseed varieties, Longyou 7 (cold-tolerant) and Lenox (cold-sensitive), were used to investigated morphological, physiological, cell and protein levels in the shoot apical meristem (SAM) of field-grown Brassica rapa to reveal the molecular mechanisms of cold stress tolerance. Compared to Lenox, Longyou 7 had a lower SAM of height, higher collar diameter. The level of malondialdehyde (MDA), SAM of height and IAA content were repressed. At the same time, compared to Lenox, the soluble sugars (SS) content, superoxide dismutase (SOD) activity, peroxidase(POD)activity, soluble protein (SP) content and collar diameter increased in Longyou 7. In total, we identified 6330 proteins, among this, 98 DAPs were expressed in L7 CK/Le CK, 107 DAPs were expressed in L7 d /Le d 183 DAPs were expressed in Le d /Le CK, 111 DAPs were expressed in L7 d /L7 CK. Quantitative real-time PCR (RT-qPCR) analysis of the coding genes for seventeen randomly selected DAPs were performed for validation. These DAPs were identified from the two winter rapa seed cultivars involved in the biological process, cellular component and molecular function analysis, which revealed glutathione transferase activity, carbohydrate-binding, and glutathione binding, glutathione metabolic process and response IAA were closely associated with the cold stress response. Some cold-induced proteins, such as glutathione S-transferase phi 2(GSTF2), might play essential roles cold acclimation in Brassica rapa of SAM. Our work will help to provide valuable information for responding to the cold stress in Brassica rapa L.