Expression profiles of glucosinolate biosynthetic genes in turnip (Brassica rapa var. rapa) at different developmental stages and effect of transformed flavin‐containing monooxygenase genes on hairy root glucosinolate content

Abstract

BACKGROUND: Glucosinolates (GSLs) are secondary metabolites, mainly existing in Brassica vegetables. Their breakdown products have health benefits and contribute to the distinctive taste of these vegetables. Because of their high value, there is a lot of interest in developing breeding strategies to increase the content of beneficial GSLs in Brassica species. GSLs are synthesized from certain amino acids and their biological roles depend largely on the structure of their side chains. Flavin-containing monooxygenase (FMO GS-OX ) genes are involved in the synthesis of these side chains. To better understand GSL biosynthesis, we sequenced the transcriptomes of turnip (Brassica rapa var. rapa) tubers at four developmental stages (S1-S4) and determined their GSL content. RESULTS:The total GSL content was high at the early stage (S1) of tuber development and increased up to S3, then decreased at S4. We detected 61 differentially expressed genes, including five FMO GS-OX genes, that were related for GSL biosynthesis among the four developmental stages. Most of these genes were highly expressed at stages S1 to S3, but their expression was much lower at S4. We estimated the effect of the five FMO GS-OX genes on GSL content by overexpressing them in turnip hairy roots and found that the amount of aliphatic GSLs increased significantly in the transgenic plants.CONCLUSION: The transcriptome data and characterization of genes involved in GSL biosynthesis, particularly the FMO GS-OX genes, will be valuable for improving the yield of beneficial GSLs in turnip and other Brassica crops.

Differences in pseudogene evolution contributed to the contrasting flavors of turnip and Chiifu, two Brassica rapa subspecies

“…Specifically, MAM controls the variability in aliphatic GSL carbon chain length, whereas AOP is responsible for modification of side chain structure ( Benderoth et al., 2009 ; Liu et al., 2014 ). Detailed analysis of five Brassica species in this study revealed considerable variation in the relative content of aliphatic GSLs among species and subspecies, consistent with the findings of earlier studies ( Chen et al., 2008 ; Yang et al., 2020 ). Previous research confirmed that there were significant differences in the GSL content of Chinese cabbage (Chiifu) germplasm, due largely to genetic changes because of selection pressure influenced by consumer preference ( Kang et al., 2006 ).…”

“…GSLs and the products of their hydrolysis are determinants of the unique taste of Brassica crops ( Bell et al., 2018 ). Compared with other Brassica species, turnips contain more aliphatic GSLs ( Yang et al., 2020 ). On the basis of the pseudogene functional annotations, we analyzed the genes involved in the aliphatic GSL metabolic pathway ( Figure 4 A and Supplemental Figure 12 ); these genes are the predominant GSL-related genes in the Brassica AA genome.…”

“…GSL content was measured as described previously ( Yang et al., 2020 ). In brief, 200 mg plant tissue was added to 80% (v/v) methanol solution containing 50 μL 1 mM sinalbin as an internal standard.…”

Comparative transcriptomic analyses of glucosinolate metabolic genes during the formation of Chinese kale seeds

“…Vegetable crops harbor a greater number of homologous genes associated with GS biosynthesis than those identified in Arabidopsis [ 36 ]. However, in Chinese kale, the homologs that play a crucial role in a specific metabolic process remain unknown, rendering it impossible to utilize gene editing for the improvement of vegetable quality.…”

Improvement of glucosinolates by metabolic engineering in Brassica crops

“…Increased amount of aliphatic GSLs was also observed in turnip (Brassica rapa var. rapa) hairy roots when overexpressing FMO GS-OX genes (Yang et al 2019).…”