Differential Regulation of Anthocyanins in Green and Purple Turnips Revealed by Combined De Novo Transcriptome and Metabolome Analysis

Abstract

Purple turnip Brassica rapa ssp. rapa is highly appreciated by consumers but the metabolites and molecular mechanisms underlying the root skin pigmentation remain open to study. Herein, we analyzed the anthocyanin composition in purple turnip (PT) and green turnip (GT) at five developmental stages. A total of 21 anthocyanins were detected and classified into the six major anthocynanin aglycones. Distinctly, PT contains 20 times higher levels of anthocyanins than GT, which explain the difference in the root skin pigmentation. We further sequenced the transcriptomes and analyzed the differentially expressed genes between the two turnips. We found that PT essentially diverts dihydroflavonols to the biosynthesis of anthocyanins over flavonols biosynthesis by strongly down-regulating one flavonol synthase gene, while strikingly up-regulating dihydroflavonol 4-reductase (DFR), anthocyanidin synthase and UDP-glucose: flavonoid-3-O-glucosyltransferase genes as compared to GT. Moreover, a nonsense mutation identified in the coding sequence of the DFR gene may lead to a nonfunctional protein, adding another hurdle to the accumulation of anthocyanin in GT. We also uncovered several key members of MYB, bHLH and WRKY families as the putative main drivers of transcriptional changes between the two turnips. Overall, this study provides new tools for modifying anthocyanin content and improving turnip nutritional quality.

RETRACTED ARTICLE: Contribution of anthocyanin pathways to fruit flesh coloration in pitayas

“…Variation of anthocyanin content in plant tissues is ascribed to the differential expression levels of key genes participating in the biosynthetic pathway [51]. Comparison of cultivars with contrasting fruit flesh colors allowed us to identify differentially expressed anthocyanin biosynthetic genes that may affect the color formation as previously documented in turnip [52], Prunus mira [53] and Lagerstromemia indica [54]. Interestingly, 12 key genes were highlighted in this study, seven of which directly involved in the anthocyanin biosynthetic pathway, were found significantly higher expressed in the colored cultivars (red and pink) as compared to the white cultivar.…”

Identification of the Genes Involved in Anthocyanin Biosynthesis and Accumulation in Taxus chinensis

“…A number of studies about transcriptomics and metabonomics in anthocyanin biosynthesis revealed that the expression levels of structural genes play an important role in anthocyanin accumulation, especially DFR, ANS, and F3H [55][56][57][58]. DFR and ANS are considered as very important enzymes in anthocyanin biosynthesis, as they could direct the flavonoid flux into the anthocyanin branch [55][56][57][58]. Previous studies showed that the expression levels of DFR, ANS, and F3H and some transcription factors were positively correlated with anthocyanin accumulation.…”

Enhanced Chlorophyll Degradation Triggers the Pod Degreening of “Golden Hook,” a Special Ecotype in Common Bean (Phaseolus vulgaris L.)

“…Anthocyanin, a class of flavonoids, localized in vacuoles, provided a wide range of colors ranging from orange/red to violet/blue. The content and variety of anthocyanins are the primary determinants of color in many fruit peel and flesh or flowers; the family of MYB and WD40 transcription factors and DFR and CHS had significant regulatory function on anthocyanin synthesis ( Wang et al, 2019 ; Zhuang et al, 2019 ).…”