Abstract
Sinapis alba is an important condiment crop and can also be used as a phytoremediation plant. Though it has important economic and agronomic values, sequence data, and the genetic tools are still rare in this plant. In the present study, a de novo transcriptome based on the transcriptions of leaves, stems, and roots was assembled for S. alba for the first time. The transcriptome contains 47,972 unigenes with a mean length of 1185 nt and an N50 of 1672 nt. Among these unigenes, 46,535 (97%) unigenes were annotated by at least one of the following databases: NCBI non-redundant (Nr), Swiss-Prot, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway, Gene Ontology (GO), and Clusters of Orthologous Groups of proteins (COGs). The tissue expression pattern profiles revealed that 3489, 1361, and 8482 unigenes were predominantly expressed in the leaves, stems, and roots of S. alba, respectively. Genes predominantly expressed in the leaf were enriched in photosynthesis- and carbon fixation-related pathways. Genes predominantly expressed in the stem were enriched in not only pathways related to sugar, ether lipid, and amino acid metabolisms but also plant hormone signal transduction and circadian rhythm pathways, while the root-dominant genes were enriched in pathways related to lignin and cellulose syntheses, involved in plant-pathogen interactions, and potentially responsible for heavy metal chelating, and detoxification. Based on this transcriptome, 14,727 simple sequence repeats (SSRs) were identified, and 12,830 pairs of primers were developed for 2522 SSR-containing unigenes. Additionally, the glucosinolate (GSL) and phytochelatin metabolic pathways, which give the characteristic flavor and the heavy metal tolerance of this plant, were intensively analyzed. The genes of aliphatic GSLs pathway were predominantly expressed in roots. The absence of aliphatic GSLs in leaf tissues was due to the shutdown of BCAT4, MAM1, and CYP79F1 expressions. Glutathione was extensively converted into phytochelatin in roots, but it was actively converted to the oxidized form in leaves, indicating the different mechanisms in the two tissues. This transcriptome will not only benefit basic research and molecular breeding of S. alba but also be useful for the molecular-assisted transfer of beneficial traits to other crops.
Highlights
Sinapis alba, known as yellow mustard or white mustard, is an important cruciferous crop widely used as food condiments in the world (Hemingway, 1995)
To construct a de novo transcriptome database, three mRNA libraries were generated from the root, stem and leaf tissues of S. alba by Illumina sequencing. ∼26.3, 27.9, and 26.4 million paired-end reads (100 bp read length) containing 5.26, 5.59, and 5.28 gigabase pairs of nucleotides were generated for the three samples, respectively, (Table 1)
The final glutathione biosynthesis step which was catalyzed by glutathione synthetase with L-γ-glutamylcysteine and glycine as substrates, showed no significant differences among the three tissues in terms of expressional levels (Figure 9D). These results indicated that the glutathione synthesis-degradation cycle was elevated in the root, followed by in the stem, and it was the lowest in the leaf tissues
Summary
Known as yellow mustard or white mustard, is an important cruciferous crop widely used as food condiments in the world (Hemingway, 1995) It has many desirable agronomic traits, such as tolerance or resistance to drought, disease, pests, and pod-shattering (Thompson, 1963; Bodnaryk and Lamb, 1991; Brown et al, 1997; Lee et al, 2014), making it an attractive resource for oil crop breeding (Tian et al, 2014). Some GSL-hydrolyzed products, such as 4-methylsulfanyl-3butenyl isothiocyanate, have been experimentally proven of their potential chemo- and cancer-prevention abilities (Abdull Razis et al, 2012) These applications exploit the advantages of GSLs. a high GSL content is a defective trait when attempting to use S. alba as an oil seed crop. Knowledge on the metabolic pathway of this plant is still limited
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