Winter rapeseed is susceptible to low temperature during winter in Northwest China, which could lead to a severe reduction of crop production. The freezing temperature could stress the whole plant, especially the leaf, and ultimately harm the survival rate of winter rapeseed. However, the molecular mechanism underlying freezing tolerance is still unclear in winter rapeseed. In this study, a comprehensive investigation of winter rapeseed freezing tolerance was conducted at the levels of transcript, protein, and physiology and biochemistry, using a pair of freezing-sensitive and freezing-resistant cultivars NQF24 and 17NTS57. There were 4,319 unique differentially expressed genes (DEGs) and 137 unique differentially abundant proteins (DAPs) between two cultivars identified in leaf under freezing stress. Function enrichment analysis showed that most of the enriched DEGs and DAPs were involved in plant hormone signal transduction, alpha-linolenic/linoleic acid metabolism, peroxisome, glutathione metabolism, fatty acid degradation, and secondary metabolite biosynthesis pathways. Based on our findings, it was speculated that freezing tolerance formation is caused by increased signal transduction, enhanced biosynthesis of protein, secondary metabolites, and plant hormones, elevated energy supply, greater reactive oxygen species scavenging, and lower lipid peroxidation as well as stronger cell stability in leaf under freezing stress. These results provide a comprehensive profile of leaf response under freezing stress, which have potential to be used as selection indicators of breeding programs to improve freezing tolerance in rapeseed.
Two winter rapeseed cultivars, “NS” (cold tolerant) and “NF” (cold sensitive), were used to reveal the morphological, physiological, and proteomic characteristics in leaves of plants after treatment at -4°C for 12 h(T1) and 24 h(T2), and at room temperature(T0), to understand the molecular mechanisms of cold tolerance. Antioxidant activity and osmotic adjustment ability were higher, and plasma membrane injury was less obvious, in NS than in NF under cold stress. We detected different abundant proteins (DAPs) related to cold tolerance in winter rapeseed through data-independent acquisition (DIA). Compared with NF, A total of 1,235 and 1,543 DAPs were identified in the NSs under T1 and T2, respectively. Compared with NF, 911 proteins were more abundant in NS only after cold treatment. Some of these proteins were related to ROS scavenging through four metabolic pathways: lysine degradation; phenylalanine, tyrosine, and tryptophan; flavonoid biosynthesis; and ubiquinone and other terpenoid-quinone biosynthesis. Analysis of these proteins in the four candidate pathways revealed that they were rapidly accumulated to quickly enhance ROS scavenging and improve the cold tolerance of NS. These proteins were noticeably more abundant during the early stage of cold stress, which was critical for avoiding ROS damage.
Winter turnip rape (Brassica rapa L.) is an important overwintering oil crop that is widely planted in northwestern China. It considered to be a good genetic resource for cold-tolerant research because its roots can survive harsh winter conditions. Here, we performed comparative transcriptomics analysis of the roots of two winter turnip rape varieties, Longyou7 (L7, strong cold tolerance) and Tianyou2 (T2, low cold tolerance), under normal condition (CK) and cold stress (CT) condition. A total of 8,366 differentially expressed genes (DEGs) were detected between the two L7 root groups (L7CK_VS_L7CT), and 8,106 DEGs were detected for T2CK_VS_T2CT. Among the DEGs, two ω-3 fatty acid desaturase (FAD3), two delta-9 acyl-lipid desaturase 2 (ADS2), one diacylglycerol kinase (DGK), and one 3-ketoacyl-CoA synthase 2 (KCS2) were differentially expressed in the two varieties and identified to be related to fatty acid synthesis. Four glutamine synthetase cytosolic isozymes (GLN), serine acetyltransferase 1 (SAT1), and serine acetyltransferase 3 (SAT3) were down-regulated under cold stress, while S-adenosylmethionine decarboxylase proenzyme 1 (AMD1) had an up-regulation tendency in response to cold stress in the two samples. Moreover, the delta-1-pyrroline-5-carboxylate synthase (P5CS), δ-ornithine aminotransferase (δ-OAT), alanine-glyoxylate transaminase (AGXT), branched-chain-amino-acid transaminase (ilvE), alpha-aminoadipic semialdehyde synthase (AASS), Tyrosine aminotransferase (TAT) and arginine decarboxylase related to amino acid metabolism were identified in two cultivars variously expressed under cold stress. The above DEGs related to amino acid metabolism were suspected to the reason for amino acids content change. The RNA-seq data were validated by real-time quantitative RT-PCR of 19 randomly selected genes. The findings of our study provide the gene expression profile between two varieties of winter turnip rape, which lay the foundation for a deeper understanding of the highly complex regulatory mechanisms in plants during cold treatment.
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