Abstract
Brassica sprouts contain abundant phytochemicals, especially glucosinolates (GSs). Various methods have been used to enhance GS content in sprouts. However, the molecular basis of GS metabolism in sprouts remains an open question. Here we employed RNA-seq analysis to compare the transcriptomes of high-GS (JL-08) and low-GS (JL-09) Brassica alboglabra sprouts. Paired-end Illumina RNA-seq reads were generated and mapped to the Brassica oleracea reference genome. The differentially expressed genes were analyzed between JL-08 and JL-09. Among these, 1477 genes were up-regulated and 1239 down-regulated in JL-09 compared with JL-08. Enrichment analysis of these differentially expressed genes showed that the GS biosynthesis had the smallest enrichment factor and the highest Q-value of all metabolic pathways in Kyoto Encyclopedia of Genes and Genomes database, indicating the main metabolic difference between JL-08 and JL-09 is the GS biosynthetic pathway. Thirty-seven genes of the sequenced data were annotated as putatively involved in GS biosynthesis, degradation, and regulation, of which 11 were differentially expressed in JL-08 and JL-09. The expression level of GS degradation enzyme myrosinase in high-GS JL-08 was lower compared with low-GS JL-09. Surprisingly, in high-GS JL-08, the expression levels of GS biosynthesis genes were also lower than those in low-GS JL-09. As the GS contents in sprouts are determined by dynamic equilibrium of seed stored GS mobilization, de novo synthesis, degradation, and extra transport, the result of this study leads us to suggest that efforts to increase GS content should focus on either raising GS content in seeds or decreasing myrosinase activity, rather than improving the expression level of GS biosynthesis genes in sprouts.
Highlights
Chinese kale (Brassica alboglabra), a cruciferous biennial vegetable plant originating in southern China, is known for its tender bolting stem and leaves and is mainly produced in Fujian and Guangdong Provinces
The high-performance liquid chromatogram of JL-09 showed greatly reduced levels of total glucosinolate as well as of individual ones compared with JL-08, and we refer to JL-09 as low-GS Chinese kale and to JL-08 as high-GS Chinese kale
RNA-Seq Analysis of Chinese Kale Sprouts Aligned with the Brassica oleracea Reference Genome Sequence
Summary
Chinese kale (Brassica alboglabra), a cruciferous biennial vegetable plant originating in southern China, is known for its tender bolting stem and leaves and is mainly produced in Fujian and Guangdong Provinces. Chemo-protective properties of GSs and their hydrolysis products against chemical carcinogens in organs including the liver, bladder, pancreas, colon, and small intestine have been well-demonstrated (Higdon et al, 2007; Razis et al, 2011; Jeffery, 2014). These compounds act as potent chemopreventive agents by promoting apoptosis in cancer cells or by inhibiting cell cycle progression, some of which have been used in clinical trials, demonstrating their potential in drug development against various cancers (Vig et al, 2009). The latter one is unstable and spontaneously become isothiocyanates, thiocyanates, nitriles, epithionitriles, or oxazolidine-2-thiones (Fahey et al, 2001)
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