Metabolic Profiling of White and Green Radish Cultivars (Raphanus sativus)

Profiling of Health-Promoting and Taste-Relevant Compounds in Sixteen Radish (Raphanus sativus L.) Genotypes Grown under Controlled Conditions

It is becoming increasingly challenging to maintain crop yields and quality as the global climate changes. The aim of this study was to determine whether and how the profile of health-promoting and taste-related compounds of radishes changes within a growing season. A total of 16 radish (Raphanus sativus L.) genotypes that are commercially available on the Czech market were assessed by means of chemical analysis. Radishes were cultivated in three independent growing cycles under controlled conditions, and the effects of the genotype and growing cycle, as well as their interactions, on the chemical traits were evaluated. Most of the variability in chemical composition was associated with the growing cycle, which accounted for 51.53% of total variance, followed by the genotype (26% of total variance). The interaction between the growing cycle and genotype explained 22.47% of total variance. The growing cycle had the strongest effect on amino acid profiles. More specifically, the amino acids that are known to contribute to overall taste (glycine, along with glutamic and aspartic acids) showed the highest degree of variation, while the amino acids related to glucosinolate biosynthesis (methionine, isoleucine, tryptophan, and phenylalanine) showed relatively low variability. On the other hand, indole glucosinolates were found to differ the most between genotypes.

Expression of RsPORB Is Associated with Radish Root Color

Radish (Raphanus sativus) plants exhibit varied root colors due to the accumulation of chlorophylls and anthocyanins compounds that are beneficial for both human health and visual quality. The mechanisms of chlorophyll biosynthesis have been extensively studied in foliar tissues but remain largely unknown in other tissues. In this study, we examined the role of NADPH:protochlorophyllide oxidoreductases (PORs), which are key enzymes in chlorophyll biosynthesis, in radish roots. The transcript level of RsPORB was abundantly expressed in green roots and positively correlated with chlorophyll content in radish roots. Sequences of the RsPORB coding region were identical between white (948) and green (847) radish breeding lines. Additionally, virus-induced gene silencing assay with RsPORB exhibited reduced chlorophyll contents, verifying that RsPORB is a functional enzyme for chlorophyll biosynthesis. Sequence comparison of RsPORB promoters from white and green radishes showed several insertions and deletions (InDels) and single-nucleotide polymorphisms. Promoter activation assays using radish root protoplasts verified that InDels of the RsPORB promoter contribute to its expression level. These results suggested that RsPORB is one of the key genes underlying chlorophyll biosynthesis and green coloration in non-foliar tissues, such as roots.

Combined widely targeted metabolomics and transcriptomics analysis reveals differentially accumulated metabolites and the underlying molecular bases in fleshy taproots of distinct radish genotypes

Radish is an important taproot crop with medicinal and edible uses that is cultivated worldwide. However, the differences in metabolites and the underlying molecular bases among different radish types remain largely unknown. In the present study, a combined analysis of liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) and RNA-Seq data was conducted to uncover important differentially accumulated metabolites (DAMs) among radish accessions with green, white and red taproot flesh colours. A total of 657 metabolites were identified and 138 DAMs were commonly present in red vs. green and red vs. white accessions. Red accessions were rich in phenolic compounds, while green and white accessions had more amino acids. Additionally, 41 metabolites and 98 genes encoding 37 enzymes were enriched in the shikimate and phenolic biosynthesis pathways. CHS is the rate-limiting enzyme determining flavonoid differences among accessions. A total of 119 candidate genes might contribute to red accession-specific accumulated metabolites. Specifically, one gene cluster consisting of 16 genes, including one RsMYB1, RsMYBL2, RsTT8, RsDFR, RsANS, Rs4CL3, RsSCPL10, Rs3AT1 and RsSAP2 gene, two RsTT19 and RsWRKY44 genes and three RsUGT genes, might be involved in anthocyanin accumulation in red radish fleshy taproots. More importantly, an InDel marker was developed based on an RsMYB1 promoter mutation, and the accuracy reached 95.9% when it was used to select red-fleshed radishes. This study provides comprehensive insights into the metabolite differences and underlying molecular mechanisms in fleshy taproots among different radish genotypes and will be beneficial for the genetic improvement of radish nutritional quality.