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      Arabidopsis R2R3-MYB transcription factor AtMYB60 functions as a transcriptional repressor of anthocyanin biosynthesis in lettuce ( Lactuca sativa)

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          Abstract

          The MYB transcription factors play important roles in the regulation of many secondary metabolites at the transcriptional level. We evaluated the possible roles of the Arabidopsis R2R3-MYB transcription factors in flavonoid biosynthesis because they are induced by UV-B irradiation but their associated phenotypes are largely unexplored. We isolated their genes by RACE-PCR, and performed transgenic approach and metabolite analyses in lettuce ( Lactuca sativa). We found that one member of this protein family, AtMYB60, inhibits anthocyanin biosynthesis in the lettuce plant. Wild-type lettuce normally accumulates anthocyanin, predominantly cyanidin and traces of delphinidin, and develops a red pigmentation. However, the production and accumulation of anthocyanin pigments in AtMYB60-overexpressing lettuce was inhibited. Using RT-PCR analysis, we also identified the complete absence or reduction of dihydroflavonol 4-reductase (DFR) transcripts in AtMYB60- overexpressing lettuce (AtMYB60-117 and AtMYB60-112 lines). The correlation between the overexpression of AtMYB60 and the inhibition of anthocyanin accumulation suggests that the transcription factorAtMYB60 controls anthocyanin biosynthesis in the lettuce leaf. Clarification of the roles of the AtMYB60 transcription factor will facilitate further studies and provide genetic tools to better understand the regulation in plants of the genes controlled by the MYB-type transcription factors. Furthermore, the characterization of AtMYB60 has implications for the development of new varieties of lettuce and other commercially important plants with metabolic engineering approaches.

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          Most cited references28

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          Flavonoids as antioxidants.

          Flavonoids are phenolic substances isolated from a wide range of vascular plants, with over 8000 individual compounds known. They act in plants as antioxidants, antimicrobials, photoreceptors, visual attractors, feeding repellants, and for light screening. Many studies have suggested that flavonoids exhibit biological activities, including antiallergenic, antiviral, antiinflammatory, and vasodilating actions. However, most interest has been devoted to the antioxidant activity of flavonoids, which is due to their ability to reduce free radical formation and to scavenge free radicals. The capacity of flavonoids to act as antioxidants in vitro has been the subject of several studies in the past years, and important structure-activity relationships of the antioxidant activity have been established. The antioxidant efficacy of flavonoids in vivo is less documented, presumably because of the limited knowledge on their uptake in humans. Most ingested flavonoids are extensively degraded to various phenolic acids, some of which still possess a radical-scavenging ability. Both the absorbed flavonoids and their metabolites may display an in vivo antioxidant activity, which is evidenced experimentally by the increase of the plasma antioxidant status, the sparing effect on vitamin E of erythrocyte membranes and low-density lipoproteins, and the preservation of erythrocyte membrane polyunsaturated fatty acids. This review presents the current knowledge on structural aspects and in vitro antioxidant capacity of most common flavonoids as well as in vivo antioxidant activity and effects on endogenous antioxidants.
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            Genetics and Biochemistry of Anthocyanin Biosynthesis.

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              Functional genomics by integrated analysis of metabolome and transcriptome of Arabidopsis plants over-expressing an MYB transcription factor.

              The integration of metabolomics and transcriptomics can provide precise information on gene-to-metabolite networks for identifying the function of unknown genes unless there has been a post-transcriptional modification. Here, we report a comprehensive analysis of the metabolome and transcriptome of Arabidopsis thaliana over-expressing the PAP1 gene encoding an MYB transcription factor, for the identification of novel gene functions involved in flavonoid biosynthesis. For metabolome analysis, we performed flavonoid-targeted analysis by high-performance liquid chromatography-mass spectrometry and non-targeted analysis by Fourier-transform ion-cyclotron mass spectrometry with an ultrahigh-resolution capacity. This combined analysis revealed the specific accumulation of cyanidin and quercetin derivatives, and identified eight novel anthocyanins from an array of putative 1800 metabolites in PAP1 over-expressing plants. The transcriptome analysis of 22,810 genes on a DNA microarray revealed the induction of 38 genes by ectopic PAP1 over-expression. In addition to well-known genes involved in anthocyanin production, several genes with unidentified functions or annotated with putative functions, encoding putative glycosyltransferase, acyltransferase, glutathione S-transferase, sugar transporters and transcription factors, were induced by PAP1. Two putative glycosyltransferase genes (At5g17050 and At4g14090) induced by PAP1 expression were confirmed to encode flavonoid 3-O-glucosyltransferase and anthocyanin 5-O-glucosyltransferase, respectively, from the enzymatic activity of their recombinant proteins in vitro and results of the analysis of anthocyanins in the respective T-DNA-inserted mutants. The functional genomics approach through the integration of metabolomics and transcriptomics presented here provides an innovative means of identifying novel gene functions involved in plant metabolism.
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                Author and article information

                Contributors
                jongsug@rda.go.kr
                rohkh@rda.go.kr
                Journal
                Plant Cell Rep
                Plant Cell Reports
                Springer-Verlag (Berlin/Heidelberg )
                0721-7714
                1432-203X
                4 March 2008
                June 2008
                : 27
                : 6
                : 985-994
                Affiliations
                [1 ]Molecular Physiology and Biochemistry Division, National Institute of Agricultural Biotechnology, Suwon, 441-707 South Korea
                [2 ]Department of Life Science, Sookmyung Women’s University, Youngsan-gu, Seoul, 140-742 South Korea
                [3 ]Department of Food and Nutrition, Sookmyung Women’s University, Youngsan-gu, Seoul, 140-742 South Korea
                [4 ]Department of Pharmacognosy Material Development, Kangwon National University, Samcheok, 245-711 South Korea
                Author notes

                Communicated by J.R. Liu.

                Article
                521
                10.1007/s00299-008-0521-1
                2413084
                18317777
                5b1742c6-90e4-40ee-9832-aeb5da2c311c
                © The Author(s) 2008
                History
                : 18 November 2007
                : 30 January 2008
                : 17 February 2008
                Categories
                Genetic Transformation and Hybridization
                Custom metadata
                © Springer-Verlag 2008

                Plant science & Botany
                r2r3-myb transcription factor,repressor,lactuca sativa,arabidopsis
                Plant science & Botany
                r2r3-myb transcription factor, repressor, lactuca sativa, arabidopsis

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