BackgroundLow temperature is a major abiotic stress affecting the production of rapeseed in China by impeding plant growth and development. A comprehensive knowledge of small-RNA expression pattern in Brassica rapa under cold stress could improve our knowledge of microRNA-mediated stress responses.ResultsA total of 353 cold-responsive miRNAs, 84 putative novel and 269 conserved miRNAs, were identified from the leaves and roots of two winter turnip rape varieties ‘Longyou 7’ (cold-tolerant) and ‘Tianyou 4’ (cold-sensitive), which were stressed under − 4 °C for 8 h. Eight conserved (miR166h-3p-1, miR398b-3p, miR398b-3p-1, miR408d, miR156a-5p, miR396h, miR845a-1, miR166u) and two novel miRNAs (Bra-novel-miR3153-5p and Bra-novel-miR3172-5p) were differentially expressed in leaves of ‘Longyou 7’ under cold stress. Bra-novel-miR3936-5p was up-regulated in roots of ‘Longyou 7’ under cold stress. Four and five conserved miRNAs were differentially expressed in leaves and roots of ‘Tianyou 4’ after cold stress. Besides, we found two conserved miRNAs (miR319e and miR166m-2) were down-regulated in non-stressed roots of ‘Longyou 7’ compared with ‘Tianyou 4’. After cold stress, we found two and eight miRNAs were differentially expressed in leaves and roots of ‘Longyou 7’ compared with ‘Tianyou 4’. The differentially expressed miRNAs between two cultivars under cold stress include novel miRNAs and the members of the miR166 and miR319 families. A total of 211 target genes for 15 known miRNAs and two novel miRNAs were predicted by bioinformatic analysis, mainly involved in metabolic processes and stress responses. Five differentially expressed miRNAs and predicted target genes were confirmed by quantitative reverse transcription PCR, and the expressional changes of target genes were negatively correlated to differentially expressed miRNAs. Our data indicated that some candidate miRNAs (e.g., miR166e, miR319, and Bra-novel-miR3936-5p) may play important roles in plant response to cold stress.ConclusionsOur work indicates that miRNA and putative target genes mediated metabolic processes and stress responses are significant to cold tolerance in B. rapa.Electronic supplementary materialThe online version of this article (10.1186/s12870-018-1242-4) contains supplementary material, which is available to authorized users.

Low ambient air temperature limits the growth and selection of crops in cold regions, and cold tolerance is a survival strategy for overwintering plants in cold winters. Studies of differences in transcriptional levels of winter rapeseed (Brassica rapa L.) under cold stress can improve our understanding of transcript-mediated cold stress responses. In this study, two winter rapeseed varieties, Longyou-7 (cold-tolerant) and Lenox (cold-sensitive), were used to reveal morphological, physiological, and transcriptome levels after 24 h of cold stress, and 24 h at room temperature, to identify the mechanism of tolerance to cold stress. Compared to Lenox, Longyou-7 has a shorter growth period and greater belowground mass, and exhibits stronger physiological activity after cold stress. Subsequently, more complete genomic annotation was obtained by sequencing. A total of 10,251 and 10,972 differentially expressed genes (DEG) were identified in Longyou-7 and Lenox, respectively. Six terms closely related to cold stress were found by the Gene Ontology (GO) function annotation. Some of these terms had greater upregulated expression in Longyou-7, and the expression of these genes was verified by qRT-PCR. Most of these DEGs are involved in phenylpropanoid biosynthesis, plant hormone signal transduction, ribosome biogenesis, MAPK signaling pathway, basal transcription factors, and photosynthesis. Analysis of the genes involved in the peroxisome pathway revealed that Longyou-7 and Lenox may have different metabolic patterns. Some transcription factors may play an important role in winter rapeseed tolerance to cold stress, and Longyou-7 is slightly slower than Lenox. Our results provide a transcriptome database and candidate genes for further study of winter rapeseed cold stress.

Winter turnip rape (Brassica rapa L.) is a large-scale winter-only oil crop cultivated in Northwest China. However, its cold-resistant molecular mechanism remains inadequate. Studying the cold adaptation mechanisms of winter turnip rape based on the proteomic technique of isobaric tags for relative and absolute quantification (iTRAQ) offers a solution to this problem. Under cold stress (−4 °C for eight hours), 51 and 94 differently accumulated proteins (DAPs) in Longyou 7 (cold-tolerant) and Tianyou 4 (cold-sensitive) were identified, respectively. These DAPs were classified into 38 gene ontology (GO) term categories, such as metabolic process, cellular process, catalytic activity, and binding. The 142 DAPs identified between the two cold-stressed cultivars were classified into 40 GO terms, including cellular process, metabolic process, cell, catalytic activity, and binding. Kyoto Encyclopedia of Genes and Genomes enrichment analysis indicated that the DAPs participated in 10 pathways. The abundance of most protein functions in ribosomes, carbon metabolism, photosynthesis, and energy metabolism including the citrate cycle, pentose phosphate pathway, and glyoxylate and dicarboxylate metabolism decreased, and the proteins that participate in photosynthesis–antenna and isoflavonoid biosynthesis increased in cold-stressed Longyou 7 compared with those in cold-stressed Tianyou 4. The expression pattern of genes encoding the 10 significant DAPs was consistent with the iTRAQ data. This study provides new information on the proteomic differences between the leaves of Longyou 7 and Tianyou 4 plants and explains the possible molecular mechanisms of cold-stress adaptation in B. rapa.