Abstract
BackgroundChinese kale (Brassica alboglabra) contains high nutritional elements and functional molecules, especially anticarcinogenic and antioxidant glucosinolates (GS), which was highly affected by environment temperature. To investigate the link of GS biosynthesis with heat stress response in Chinese kale, global transcription profiles of high-GS line (HG), low-GS line (LG), high-GS line under heat stress (HGT) and low-GS line under heat stress (LGT) were analyzed.ResultsBased on three biological replicates of each RNA sequencing data, 3901, 4062 and 2396 differentially expressed genes in HG vs HGT, LG vs LGT and HGT vs LGT were obtained, respectively. GO annotation, KEGG pathway analysis and a comprehensive analysis of DEGs showed a strong correlation between the GS biosynthesis and heat stress response. It was noticed that 11 differentially expressed genes tied to the GS biosynthesis were down-regulated, 23 heat shock transcription factors and 61 heat shock proteins were up-regulated upon the heat treatment. Another two Chinese kale varieties Cuibao and Shunbao with high- and low- GS content respectively, were used to validate the relationship of GS content and heat-response, and the results showed that high-GS content variety were more thermotolerant than the low-GS content one although GS significantly decreased in both varieties under heat stress. In addition, HSP100/ClpB, HSP90, HSP70 and sHSPs were differentially expressed in high- and low-GS varieties. Notably, HSP90 and sHSPs showed an obviously early response to heat stress than other related genes.ConclusionThe higher heat resistance of high-GS Chinese kale and the sharp decrease of glucosinolate content under heat stress indicated a strong relationship of GS accumulation and heat stress response. Combined with the previous report on the low expression of HSP90 at elevated temperatures in GS-deficient mutant TU8 of Arabidopsis, the differential expression pattern of HSP90 in high- and low- GS varieties and its early heat response implied it might be a key regulator in GS metabolism and heat-resistance in Chinese kale.
Highlights
Chinese kale (Brassica alboglabra) contains high nutritional elements and functional molecules, especially anticarcinogenic and antioxidant glucosinolates (GS), which was highly affected by environment temperature
Combining the profiles and contents of GS in another two Chinese kale varieties with high- and low- GS content respectively, and quantitative real-time PCR assay of Heat shock transcription factors (HSF) and Heat shock proteins (HSPs) genes, we revealed a strong correlation between GS biosynthesis and heat stress response
Analysis of differentially expressed genes (DEGs) involved in GS biosynthesis First of all, we found that 25 genes and 10 transcription factors related to GS biosynthesis altogether were differentially expressed (Tables 2 and 3), and almost all DEGs in high-GS line (HG) vs High-GS line treated with heat stress (HGT) and LowGS line (LG) vs Low-GS line treated with heat stress (LGT) were down-regulated and accounted for the decline of GS content under heat stress
Summary
Chinese kale (Brassica alboglabra) contains high nutritional elements and functional molecules, especially anticarcinogenic and antioxidant glucosinolates (GS), which was highly affected by environment temperature. Known as Chinese kale or Kai Lan, is widely distributed in Southern China and Southeast Asia [1]. GS known as mustard oil glucosides, are a group of nitrogen- and sulfur-rich secondary metabolites, mainly found in the order Capparales. They can be grouped into indole, aliphatic, and aromatic GS according to the characteristic of the amino acids they are derived from, such as Trp (indole GS), Ala, Ile, Leu, Met, or Val (aliphatic GS), and Phe or Tyr (aromatic GS) [5,6,7]. A wide variety of crucial transcriptional factors and biosynthetic genes involved in the GS metabolism and regulation of B. oleracea [9], B. alboglabra [2, 3, 10], B. rapa [11, 12] were identified and studied
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