BackgroundWatercress (Nasturtium officinale R. Br.) is an aquatic herb species that is a rich source of secondary metabolites such as glucosinolates. Among these glucosinolates, watercress contains high amounts of gluconasturtiin (2-phenethyl glucosinolate) and its hydrolysis product, 2-phennethyl isothiocyanate, which plays a role in suppressing tumor growth. However, the use of N. officinale as a source of herbal medicines is currently limited due to insufficient genomic and physiological information.ResultsTo acquire precise information on glucosinolate biosynthesis in N. officinale, we performed a comprehensive analysis of the transcriptome and metabolome of different organs of N. officinale. Transcriptome analysis of N. officinale seedlings yielded 69,570,892 raw reads. These reads were assembled into 69,635 transcripts, 64,876 of which were annotated to transcripts in public databases. On the basis of the functional annotation of N. officinale, we identified 33 candidate genes encoding enzymes related to glucosinolate biosynthetic pathways and analyzed the expression of these genes in the leaves, stems, roots, flowers, and seeds of N. officinale. The expression of NoMYB28 and NoMYB29, the main regulators of aliphatic glucosinolate biosynthesis, was highest in the stems, whereas the key regulators of indolic glucosinolate biosynthesis, such as NoDof1.1, NoMYB34, NoMYB51, and NoMYB122, were strongly expressed in the roots. Most glucosinolate biosynthetic genes were highly expressed in the flowers. HPLC analysis enabled us to detect eight glucosinolates in the different organs of N. officinale. Among these glucosinolates, the level of gluconasturtiin was considerably higher than any other glucosinolate in individual organs, and the amount of total glucosinolates was highest in the flower.ConclusionsThis study has enhanced our understanding of functional genomics of N. officinale, including the glucosinolate biosynthetic pathways of this plant. Ultimately, our data will be helpful for further research on watercress bio-engineering and better strategies for exploiting its anti-carcinogenic properties.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-017-3792-5) contains supplementary material, which is available to authorized users.

Mizuna (Brassica rapa L. var. japonica), a member of the family Brassicaceae, is rich in various health-beneficial phytochemicals, such as glucosinolates, phenolics, and anthocyanins. However, few studies have been conducted on genes associated with metabolic traits in mizuna. Thus, this study provides a better insight into the metabolic differences between green and red mizuna via the integration of transcriptome and metabolome analyses. A mizuna RNAseq analysis dataset showed 257 differentially expressed unigenes (DEGs) with a false discovery rate (FDR) of <0.05. These DEGs included the biosynthesis genes of secondary metabolites, such as anthocyanins, glucosinolates, and phenolics. Particularly, the expression of aliphatic glucosinolate biosynthetic genes was higher in the green cultivar. In contrast, the expression of most genes related to indolic glucosinolates, phenylpropanoids, and flavonoids was higher in the red cultivar. Furthermore, the metabolic analysis showed that 14 glucosinolates, 12 anthocyanins, five phenolics, and two organic acids were detected in both cultivars. The anthocyanin levels were higher in red than in green mizuna, while the glucosinolate levels were higher in green than in red mizuna. Consistent with the results of phytochemical analyses, the transcriptome data revealed that the expression levels of the phenylpropanoid and flavonoid biosynthesis genes were significantly higher in red mizuna, while those of the glucosinolate biosynthetic genes were significantly upregulated in green mizuna. A total of 43 metabolites, such as amino acids, carbohydrates, tricarboxylic acid (TCA) cycle intermediates, organic acids, and amines, was identified and quantified in both cultivars using gas chromatography coupled with time-of-flight mass spectrometry (GC-TOFMS). Among the identified metabolites, sucrose was positively correlated with anthocyanins, as previously reported.

Glucosinolates are secondary metabolites that play important roles in plant defense and human health, as their production in plants is enhanced by overexpressing transcription factors. Here, four cabbage transcription factors (IQD1−1, IQD1−2, MYB29−1, and MYB29−2) affecting genes in both aliphatic and indolic glucosinolates biosynthetic pathways and increasing glucosinolates accumulation were overexpressed in watercress. Five IQD1−1, six IQD1−2, five MYB29−1, six MYB29−2, and one GUS hairy root lines were created. The expression of all genes involved in glucosinolates biosynthesis was higher in transgenic lines than in the GUS hairy root line, in agreement with total glucosinolates contents, determined by highperformance liquid chromatography. In transgenic IQD1−1 (1), IQD1−2 (4), MYB29−1 (2), and MYB29−2 (1) hairy root lines, total glucosinolates were 3.39-, 3.04-, 2.58-, and 4.69-fold higher than those in the GUS hairy root lines, respectively. These results suggest a central regulatory function for IQD1−1, IQD1−2, MYB29−1, and MYB29−2 transcription factors in glucosinolates biosynthesis in watercress hairy roots.

This study aimed to investigate the effects of various growth media and three types of auxins on glucosinolate biosynthesis in hairy root cultures of kale (Brassica oleracea var. acephala). Four different glucosinolates (4-hydroxyglucobrassicin, glucobrassicin, 4-methoxyglucobrassicin, and neoglucobrassicin) were used in this study. The accumulation of glucosinolates was influenced by both media and auxin treatments. Of the media treatments, full-strength Gamborg's B5 medium (B5) supported the highest accumulation of total glucosinolates, followed by full-strength Murashige-Skoog medium (MS), whereas the lowest glucosinolates accumulation was in the half-strength MS medium treatment. The accumulation of glucobrassicin was very high, followed by 4-methoxyglucobrassicin, irrespective of the growth medium used. The highest content of glucobrassicin was measured in cultures in B5 medium, while MS medium resulted in the highest accumulation of 4-methoxyglucobrassicin. Half-strength B5 medium resulted in the highest content of neoglucobrassicin, and Schenk and Hildebrandt medium (SH) supported the highest content of 4-hydroxyglucobrassicin. The total and individual levels of glucosinolates in hairy root cultures of kale were all influenced by exposure to the nine auxin treatments, with the exception glucobrassicin. In general, levels of glucosinolate decreased with increasing concentrations of auxins. Treatment with the auxin indole-3-butyric acid (IBA) 0.1 resulted in the highest total concentration of glucosinolates, measuring 1.83 times higher than that of hairy root cultures treated with naphthalene acetic acid (NAA) 1.0, which resulted in the lowest glucosinolate concentrations. Of the four glucosinolates, glucobrassicin and 4-methoxyglucobrassicin contents were considerably higher. The auxin IBA 0.1 promoted the highest 4-methoxyglucobrassicin accumulation in the hairy root cultures of kale. The auxin treatment indole-3-acetic acid (IAA) 0.1 resulted in the highest amount of 4-hydroxyglucobrassicin and neoglucobrassicin. Hairy root cultures could be a valuable alternative approach for the production of glucosinolate compounds from kale.

Here, accumulation of glucosinolates and expression of glucosinolates biosynthesis genes in green and red mustard hairy roots were identified and quantified by HPLC and RT-PCR analyses. The total glucosinolates content of green mustard hairy root (10.09 µg/g dry weight) was 3.88 times higher than that of red mustard hairy root. Indolic glucosinolates (glucobrassicin, 4-methoxyglucobrassicin, and neoglucobrassicin) in green mustard were found at 30.92, 6.95, and 5.29 times higher than in red mustard hairy root, respectively. Conversely, levels of glucotropaeolin (aromatic glucosinolate) was significantly higher in red mustard than in green mustard. Accumulation of glucoraphasatin, an aliphatic glucosinolate, was only observed only in red mustard hairy roots. Quantitative real-time PCR analysis showed that the expression level of genes related to aliphatic and aromatic glucosinolate biosynthesis were higher in red mustard, exception. The expression of , which encodes a key enzyme involved in the indolic glucosinolate biosynthetic pathway, was higher in green mustard than in red mustard. Additionally, to further distinguish between green mustard and red mustard hairy roots, hydrophilic and lipophilic compounds were identified by gas chromatography-mass spectrometry and subjected to principal component analysis. The results indicated that core primary metabolites and glucosinolate levels were higher in the hairy roots of green mustard than in those of red mustard.