Identification and differential expression analysis of anthocyanin biosynthetic genes in root-skin color variants of radish (Raphanus sativus L.)

Comparative transcriptome analysis reveals transcriptional regulation of anthocyanin biosynthesis in purple radish (Raphanus sativus L.)

Radish exhibits significant variation in color, particularly in sprouts, leaves, petals, fleshy roots, and other tissues, displaying a range of hues such as green, white, red, purple, and black. Although extensive research has been conducted on the color variation of radish, the underlying mechanism behind the variation in radish flower color remains unclear. To date, there is a lack of comprehensive research investigating the variation mechanism of radish sprouts, leaves, fleshy roots, and flower organs. This study aims to address this gap by utilizing transcriptome sequencing to acquire transcriptome data for white and purple radish flowers. Additionally, the published transcriptome data of sprouts, leaves, and fleshy roots were incorporated to conduct a systematic analysis of the regulatory mechanisms underlying anthocyanin biosynthesis in these four radish tissues. The comparative transcriptome analysis revealed differential expression of the anthocyanin biosynthetic pathway genes DFR, UGT78D2, TT12 and CPC in the four radish tissues. Additionally, the WGCNA results identified RsDFR.9c and RsUGT78D2.2c as hub genes responsible for regulating anthocyanin biosynthesis. By integrating the findings from the comparative transcriptome analysis, WGCNA, and anthocyanin biosynthetic pathway-related gene expression patterns, it is hypothesized that genes RsDFR.9c and RsUGT78D2.2c may serve as pivotal regulators of anthocyanins in the four radish tissues. Furthermore, the tissue-specific expression of the four copies of RsPAP1 is deemed crucial in governing anthocyanin synthesis and accumulation. Our results provide new insights into the molecular mechanism of anthocyanin biosynthesis and accumulation in different tissues of radish.

Molecular Regulatory Network of Anthocyanin Accumulation in Black Radish Skin as Revealed by Transcriptome and Metabonome Analysis

To understand the coloring mechanism in black radish, the integrated metabolome and transcriptome analyses of root skin from a black recombinant inbred line (RIL 1901) and a white RIL (RIL 1911) were carried out. A total of 172 flavonoids were detected, and the analysis results revealed that there were 12 flavonoid metabolites in radish root skin, including flavonols, flavones, and anthocyanins. The relative concentrations of most flavonoids in RIL 1901 were higher than those in RIL 1911. Meanwhile, the radish root skin also contained 16 types of anthocyanins, 12 of which were cyanidin and its derivatives, and the concentration of cyanidin 3-o-glucoside was very high at different development stages of black radish. Therefore, the accumulation of cyanidin and its derivatives resulted in the black root skin of radish. In addition, a module positively related to anthocyanin accumulation and candidate genes that regulate anthocyanin synthesis was identified by the weighted gene co-expression network analysis (WGCNA). Among them, structural genes (RsCHS, RsCHI, RsDFR, and RsUGT75C1) and transcription factors (TFs) (RsTT8, RsWRKY44L, RsMYB114, and RsMYB308L) may be crucial for the anthocyanin synthesis in the root skin of black radish. The anthocyanin biosynthesis pathway in the root skin of black radish was constructed based on the expression of genes related to flavonoid and anthocyanin biosynthesis pathways (Ko00941 and Ko00942) and the relative expressions of metabolites. In conclusion, this study not only casts new light on the synthesis and accumulation of anthocyanins in the root skin of black radish but also provides a molecular basis for accelerating the cultivation of new black radish varieties.

The long noncoding RNA LINC15957 regulates anthocyanin accumulation in radish

Radish (Raphanus sativus L.) is an important root vegetable crop belonging to the Brassicaceae family. Anthocyanin rich radish varieties are popular among consumers because of their bright color and high nutritional value. However, the underlying molecular mechanism responsible for skin and flesh induce anthocyanin biosynthesis in transient overexpression, gene silencing and transcriptome sequencing were used to verify its function in radish anthocyanin accumulation, radish remains unclear. Here, we identified a long noncoding RNA LINC15957, overexpression of LINC15957 was significantly increased anthocyanin accumulation in radish leaves, and the expression levels of structural genes related to anthocyanin biosynthesis were also significantly increased. Anthocyanin accumulation and expression levels of anthocyanin biosynthesis genes were significantly reduced in silenced LINC15957 flesh when compared with control. By the transcriptome sequencing of the overexpressed LINC15957 plants and the control, 5,772 differentially expressed genes were identified. A total of 3,849 differentially expressed transcription factors were identified, of which MYB, bHLH, WD40, bZIP, ERF, WRKY and MATE were detected and differentially expressed in the overexpressed LINC15957 plants. KEGG enrichment analysis revealed the genes were significant enriched in tyrosine, L-Phenylalanine, tryptophan, phenylpropanol, and flavonoid biosynthesis. RT-qPCR analysis showed that 8 differentially expressed genes (DEGs) were differentially expressed in LINC15957-overexpressed plants. These results suggested that LINC15957 involved in regulate anthocyanin accumulation and provide abundant data to investigate the genes regulate anthocyanin biosynthesis in radish.

Anthocyanin Biosynthesis Associated with Natural Variation in Autumn Leaf Coloration in Quercus aliena Accessions

Quercus aliena is an economically important tree species and one of the dominant native oak species in China. Although its leaves typically turn yellow in autumn, we observed natural variants with red leaves. It is important to understand the mechanisms involved in leaf color variation in this species. Therefore, we compared a Q. aliena tree with yellow leaves and three variants with red leaves at different stages of senescence in order to determine the causes of natural variation. We found that the accumulation of anthocyanins such as cyanidin 3-O-glucoside and cyanidin 3-O-sambubiglycoside had a significant effect on leaf coloration. Gene expression analysis showed upregulation of almost all genes encoding enzymes involved in anthocyanin synthesis in the red-leaved variants during the early and main discoloration stages of senescence. These findings are consistent with the accumulation of anthocyanin in red variants. Furthermore, the variants showed significantly higher expression of transcription factors associated with anthocyanin synthesis, such as those encoded by genes QaMYB1 and QaMYB3. Our findings provide new insights into the physiological and molecular mechanisms involved in autumn leaf coloration in Q. aliena, as well as provide genetic resources for further development and cultivation of valuable ornamental variants of this species.

Intron-retained radish (Raphanus sativus L.) RsMYB1 transcripts found in colored-taproot lines enhance anthocyanin accumulation in transgenic Arabidopsis plants

KEY MESSAGE

Overexpression of the naturally occurring intron-retained (IR) forms of radish RsMYB1 and RsTT8 transcripts in Arabidopsis causes a substantial increase in anthocyanin accumulation. The production of anthocyanins in plants is tightly controlled by the MYB-bHLH-WD40 (MBW) complex. In this study, analysis of four radish (Raphanus sativus L.) inbred lines with different colored taproots revealed that regulatory genes of anthocyanin biosynthesis, RsMYB1 and RsTT8, produce three transcripts, one completely spliced and two intron retention (IR1 and IR2) forms. Transcripts RsMYB1-IR1 and RsMYB1-IR2 retained the 1st (380 nt) and 2nd (149 nt) introns, respectively; RsTT8-IR1 retained the 4th intron (113 nt); RsTT8-IR2 retained both the 3rd (128 nt) and 4th introns. Levels of most IR forms were substantially low in radish samples, but the RsTT8-IR2 level was higher than RsTT8 in red skin/red flesh (RsRf) root. Since all IR forms contained a stop codon within the intron, they were predicted to encode truncated proteins with defective interaction domains, resulting in the inability to form the MBW complex in vivo. However, tobacco leaves transiently co-expressing RsMYB1-IRs and RsTT8-IRs showed substantially higher anthocyanin accumulation than those co-expressing their spliced forms. Consistently, co-expression of constructs encoding truncated proteins with spliced or IR forms of their interaction partner in tobacco leaves did not result in anthocyanin accumulation. Compared with RsMYB1, the overexpression of RsMYB1-IRs in Arabidopsis pap1 mutant increased anthocyanin accumulation by > sevenfold and upregulated the expression of Arabidopsis flavonoid biosynthesis genes including AtTT8. Our results suggest that the stable co-expression of RsMYB1-IRs in fruit trees and vegetable crops could be used to increase their anthocyanin contents.

Development of Molecular Markers for Predicting Radish (Raphanus sativus) Flesh Color Based on Polymorphisms in the RsTT8 Gene

Red radish (Raphanus sativus L.) cultivars are a rich source of health-promoting anthocyanins and are considered a potential source of natural colorants used in the cosmetic industry. However, the development of red radish cultivars via conventional breeding is very difficult, given the unusual inheritance of the anthocyanin accumulation trait in radishes. Therefore, molecular markers linked with radish color are needed to facilitate radish breeding. Here, we characterized the RsTT8 gene isolated from four radish genotypes with different skin and flesh colors. Sequence analysis of RsTT8 revealed a large number of polymorphisms, including insertion/deletions (InDels), single nucleotide polymorphisms (SNPs), and simple sequence repeats (SSRs), between the red-fleshed and white-fleshed radish cultivars. To develop molecular markers on the basis of these polymorphisms for discriminating between radish genotypes with different colored flesh tissues, we designed four primer sets specific to the RsTT8 promoter, InDel, SSR, and WD40/acidic domain (WD/AD), and tested these primers on a diverse collection of radish lines. Except for the SSR-specific primer set, all primer sets successfully discriminated between red-fleshed and white-fleshed radish lines. Thus, we developed three molecular markers that can be efficiently used for breeding red-fleshed radish cultivars.

Differential Regulation of Anthocyanins in Cerasus humilis Fruit Color Revealed by Combined Transcriptome and Metabolome Analysis

Coloring is an important appearance quality of fruit. In order to evaluate the relationship between metabolites and fruit color, we analyzed the metabolites and transcriptional profiles of two different Cerasus humilis cultivars: “RF” (cv. Zhangwu, red fruit) and “YF” (cv. Nongda No.5, yellow fruit). The results of identification and quantification of metabolites showed that there were significant differences in the contents of 11 metabolites between RF and YF. Transcriptomics was used to analyze the expression patterns of genes related to the anthocyanin biosynthesis pathway, and subsequently, the regulation network of anthocyanin biosynthesis was established to explore their relationship with color formation. QRT-PCR, performed for 12 key genes, showed that the expression profiles of the differentially expressed genes were consistent with the results of the transcriptome data. A co-expression analysis revealed that the late genes were significantly positively correlated with most of the different metabolites. The results of the study provide a new reference for improving the fruit color of Cerasus humilis in the future.