Abstract
Winter rapeseed (Brassica rapa L.) is a major oilseed crop in Northern China, where its production was severely affected by chilling and freezing stress. However, not much is known about the role of differentially accumulated proteins (DAPs) during the chilling and freezing stress. In this study, isobaric tag for relative and absolute quantification (iTRAQ) technology was performed to identify DAPs under freezing stress. To explore the molecular mechanisms of cold stress tolerance at the cellular and protein levels, the morphological and physiological differences in the shoot apical meristem (SAM) of two winter rapeseed varieties, Longyou 7 (cold-tolerant) and Lenox (cold-sensitive), were explored in field-grown plants. Compared to Lenox, Longyou 7 had a lower SAM height and higher collar diameter. The level of malondialdehyde (MDA) and indole-3-acetic acid (IAA) content was also decreased. Simultaneously, the soluble sugars (SS) content, superoxide dismutase (SOD) activity, peroxidase (POD) activity, soluble protein (SP) content, and collar diameter were increased in Longyou 7 as compared to Lenox. A total of 6330 proteins were identified. Among this, 98, 107, 183 and 111 DAPs were expressed in L7 CK/Le CK, L7 d/Le d, Le d/Le CK and L7 d/L7 CK, respectively. Quantitative real-time PCR (RT-qPCR) analysis of the coding genes for seventeen randomly selected DAPs was performed for validation. These DAPs were identified based on gene ontology enrichment analysis, which revealed that glutathione transferase activity, carbohydrate-binding, glutathione binding, metabolic process, and IAA response were closely associated with the cold stress response. In addition, some cold-induced proteins, such as glutathione S-transferase phi 2(GSTF2), might play an essential role during cold acclimation in the SAM of Brassica rapa. The present study provides valuable information on the involvement of DAPs during cold stress responses in Brassica rapa L, and hence could be used for breeding experiments.
Highlights
Brassica winter rapeseed (Brassica rapa L.) is an effective surface cover oil crop that can survive the winters of northern China in the cold and arid region
When grown in an open field, the height of the shoot apical meristem (SAM) levels was measured at the different growth stages
Our study showed that higher SAM height indicated relatively high levels of indole-3-acetic acid (IAA) content, while a relatively smaller SAM indicated relatively low levels of IAA content; auxin content is profoundly related to the SAM height
Summary
Brassica winter rapeseed (Brassica rapa L.) is an effective surface cover oil crop that can survive the winters of northern China in the cold and arid region. A differential proteomics approach using an isobaric tag for relative and absolute quantification (iTRAQ) was e mployed[14] This gel-free mass spectrometry technique has been successfully applied to identify differentially accumulated proteins involved in stress response across various plants such as Vitis amurensis[15], Triticum aestivum[16], Gossypium hirsutum L17, Lycopersicon esculentum Mill[18], Brassica rapa L19, and Spica Prunellae[20]. Proteins showing localized differences in abundance can be targets for marker-assisted selection and used to improve breeding efficiency[14] This knowledge gives fundamental insight into the direct role of the SAM in controlling abiotic stress tolerance in plants
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