Transcriptome Profile Analysis of Winter Rapeseed (Brassica napus L.) in Response to Freezing Stress, Reveal Potentially Connected Events to Freezing Stress

Abstract

Winter rapeseed is not only an important oilseed crop, but also a winter cover crop in Northern China, where its production was severely limited by freezing stress. As an overwinter crop, the production is severely limited by freezing stress. Therefore, understanding the physiological and molecular mechanism of winter rapeseed (Brassica napus L.) in freezing stress responses becomes essential for the improvement and development of freezing-tolerant varieties of Brassica napus. In this study, morphological, physiological, ultrastructure and transcriptome changes in the Brassica napus line “2016TS(G)10” (freezing-tolerance line) that was exposed to –2 °C for 0 h, 1 h, 3 h and 24 h were characterized. The results showed that freezing stress caused seedling dehydration, and chloroplast dilation and degradation. The content of malondialdehyde (MDA), proline, soluble protein and soluble sugars were increased, as well as the relative electrolyte leakage (REL) which was significantly increased at frozen 24 h. Subsequently, RNA-seq analysis revealed a total of 98,672 UniGenes that were annotated in Brassica napus and 3905 UniGenes were identified as differentially expressed genes after being exposed to freezing stress. Among these genes, 2312 (59.21%) were up-regulated and 1593 (40.79%) were down-regulated. Most of these DEGs were significantly annotated in the carbohydrates and energy metabolism, signal transduction, amino acid metabolism and translation. Most of the up-regulated DEGs were especially enriched in plant hormone signal transduction, starch and sucrose metabolism pathways. Transcription factor enrichment analysis showed that the AP2/ERF, WRKY and MYB families were also significantly changed. Furthermore, 20 DEGs were selected to validate the transcriptome profiles via quantitative real-time PCR (qRT-PCR). In conclusion, the results provide an overall view of the dynamic changes in physiology and insights into the molecular regulation mechanisms of winter Brassica napus in response to freezing treatment, expanding our understanding on the complex molecular mechanism in plant response to freezing stress.

Physiological and Biochemical Mechanisms and Cytology of Cold Tolerance in Brassica napus

“…This result showed that ROS induced lipid peroxidation and the level of injury depended on the cold-resistant properties of the cultivars. Our findings are in agreement with previous study that cold-tolerant species, such as Santalum album (Zhang et al, 2017), Vitis amurensis (Xu et al, 2014), Solanum lycopersicum (Chen et al, 2015), B. rape (Ma et al, 2019), and B. napus (Pu et al, 2019a) have strong protective enzyme activity and high content of soluble regulators which can reduce ROS production. The present physiochemical study confirmed that cultivar 16NTS309 had significantly higher cold resistance than cultivar Tianyou2238.…”

“…In the present study, more obvious ultrastructural alterations in leaf mesophyll including the damage of membrane system, destruction of chloroplast and swelling of mitochondria were observed in cold-sensitive variety of Tianyou2238 compared to cold-resistant cultivar 16NTS309. Similar damage in the leaf mesophyll cell ultrastructures was investigated in B. napus against cold stress ( Stefanowska et al., 2002 ; Pu et al., 2019a ). Previous research reported that chloroplasts are thought to be the first and most severely affected organelle ( Kratsch and Wise, 2000 ), and cold stress may lead to unstacking of grana and disintegration of the chloroplast envelope ( Klein, 1960 ; Kislyuk, 1963 ; Jagels, 1970 ; Taylor and Craig, 1971 ; Murphy and Wilson, 1981 ; Kratsch and Wise, 2000 ; Vella et al., 2012 ).…”

Isoform Sequencing Provides Insight Into Freezing Response of Common Wheat (Triticum aestivum L.)

“…Relative electrolyte leakage was regarded as the direct marker to reflect the membrane damage by freezing stress in previous studies (Campos et al, 2003;Pu et al, 2019). According to the relative electrolyte leakage and the damage level of seedling ( Supplementary Figure S1), we selected leaves treated 4 h at −6 • C to conduct RNA extraction and transcriptome sequencing.…”

“…Transcriptome sequencing has been proven to be an efficient method for cold-related gene discovery, which has been studied extensively in Arabidopsis (Lee et al, 2005) and cereal crops such as rice (Zhang et al, 2012), maize (Trzcinska-Danielewicz et al, 2009), barley (Tommasini et al, 2008), and wheat (Gulick et al, 2005). RNA-seq has discovered several cold-related pathways and a series of key coldresponsive genes (Laudencia-Chingcuanco et al, 2011;Pu et al, 2019).…”

Transcriptomic Profiling of Young Cotyledons Response to Chilling Stress in Two Contrasting Cotton (Gossypium hirsutum L.) Genotypes at the Seedling Stage

“…In the present study, we detected one BRI1 gene and 12 TCH4 genes predominantly expressed in T24 and found that most genes in the BR signaling pathway were exclusively present in the blue module, indicating that BR signaling was necessary for cotyledon cold tolerance. Additionally, some studies have demonstrated that genes involved in the auxin signaling pathway are differentially expressed when plants are subjected to cold stress [30,69]. In these remarkable modules, we identified 136 genes involved in plant hormone signaling pathway, of which 46 were related to auxin signal transduction, most of which were from the blue module, indicating that auxin played a significant role in regulating cotyledon cold tolerance.…”