Abstract
Rapeseed (Brassica napus L.) is an important oilseed crop in the world. Its productivity is significantly influenced by numerous abiotic stresses, including cold stress (CS). Consequently, enhancement in CS tolerance is becoming an important area for agricultural investigation and crop improvement. Therefore, the current study aimed to identify the stress-responsive genes, metabolites, and metabolic pathways based on a combined transcriptome and metabolome analysis to understand the CS responses and tolerance mechanisms in the cold-tolerant (C18) and cold-sensitive (C6) rapeseed varieties. Based on the metabolome analysis, 31 differentially accumulated metabolites (DAMs) were identified between different comparisons of both varieties at the same time points. From the transcriptome analysis, 2,845, 3,358, and 2,819 differentially expressed genes (DEGs) were detected from the comparison of C6-0 vs. C18-0, C6-1 vs. C18-1, and C6-7 vs. C18-7. By combining the transcriptome and metabolome data sets, we found that numerous DAMs were strongly correlated with several differentially expressed genes (DEGs). A functional enrichment analysis of the DAMs and the correlated DEGs specified that most DEGs and DAMs were mainly enriched in diverse carbohydrates and amino acid metabolisms. Among them, starch and sucrose metabolism and phenylalanine metabolism were significantly enriched and played a vital role in the CS adaption of rapeseed. Six candidate genes were selected from the two pathways for controlling the adaption to low temperature. In a further validation, the T-DNA insertion mutants of their Arabidopsis homologous, including 4cl3, cel5, fruct4, ugp1, axs1, and bam2/9, were characterized and six lines differed significantly in levels of freezing tolerance. The outcome of the current study provided new prospects for the understanding of the molecular basis of CS responses and tolerance mechanisms in rapeseed and present a set of candidate genes for use in improving CS adaptability in the same plant.
Highlights
Rapeseed (Brassica napus L.) is an essential oilseed crop
The MDA content was considerably higher in cold stress (CS)-C6 compared to CT-C18 (Figure 1D), indicating that CT-C18 had a better capacity to cope with oxidative stress than CS-C6
The present study performed a conjoint analysis based on transcriptomes and metabolomes to identify the key genes, metabolites, and metabolic pathways related to CS response in tolerant and sensitive rapeseed varieties
Summary
Rapeseed (Brassica napus L.) is an essential oilseed crop. Due to the high oil content in its seeds, it is considered to account for one-third of the total edible oils throughout the world, which helps in the mass production of animal feed and vegetable oil (Jiang et al, 2014). Rapeseed is sensitive to several abiotic stresses, such as drought, salinity, flood, and cold, severely reducing the growth and production of the crop, resulting in agricultural economic loss and production risks (Raza, 2020a). CS seriously reduces the rate and uniformity of germination, hampers seedling vigor, and delays plant development, resulting in serious crop yield losses (He et al, 2021; Raza et al, 2021b). Severe winter freezing temperatures affected 77.8% of the rapeseed growing area and caused significant production and yield loss in China (Zhang et al, 2008). New seedlings, flowering, and seed formation are mainly affected by CS (Lardon and Triboi-Blondel, 1995; Shafighi et al, 2020). It is urgent to develop CS-tolerant rapeseed varieties to ensure yield under such unfavorable conditions
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