title: A pomegranate (Punica granatum L.) WD40-repeat gene is a functional homologue of Arabidopsis TTG1 and is involved in the regulation of anthocyanin biosynthesis during pomegranate fruit development.
abstract: Anthocyanins are the major pigments responsible for the pomegranate (Punica granatum L.) fruit skin color. The high variability in fruit external color in pomegranate cultivars reflects variations in anthocyanin composition. To identify genes involved in the regulation of anthocyanin biosynthesis pathway in the pomegranate fruit skin we have isolated, expressed and characterized the pomegranate homologue of the Arabidopsis thaliana TRANSPARENT TESTA GLABRA1 (TTG1), encoding a WD40-repeat protein. The TTG1 protein is a regulator of anthocyanins and proanthocyanidins (PAs) biosynthesis in Arabidopsis, and acts by the formation of a transcriptional regulatory complex with two other regulatory proteins: bHLH and MYB. Our results reveal that the pomegranate gene, designated PgWD40, recovered the anthocyanin, PAs, trichome and seed coat mucilage phenotype in Arabidopsis ttg1 mutant. PgWD40 expression and anthocyanin composition in the skin were analyzed during pomegranate fruit development, in two accessions that differ in skin color intensity and timing of appearance. The results indicate high positive correlation between the total cyanidin derivatives quantity (red pigments) and the expression level of PgWD40. Furthermore, strong correlation was found between the steady state levels of PgWD40 transcripts and the transcripts of pomegranate homologues of the structural genes PgDFR and PgLDOX. PgWD40, PgDFR and PgLDOX expression also correlated with the expression of pomegranate homologues of the regulatory genes PgAn1 (bHLH) and PgAn2 (MYB). On the basis of our results we propose that PgWD40 is involved in the regulation of anthocyanin biosynthesis during pomegranate fruit development and that expression of PgWD40, PgAn1 and PgAn2 in the pomegranate fruit skin is required to regulate the expression of downstream structural genes involved in the anthocyanin biosynthesis.
authors.affiliation: Unit of Deciduous Fruit Tree Sciences, Newe Ya'ar Research Center, Agricultural Research Organization, P.O. Box 1021, 30095, Ramat Yishay, Israel. zohar@agri.gov.il
authors.forename: Zohar
authors.initials: Z
authors.lastname: Ben-Simhon
authors.forename: Sylvie
authors.initials: S
authors.lastname: Judeinstein
authors.forename: Talia
authors.initials: T
authors.lastname: Nadler-Hassar
authors.forename: Taly
authors.initials: T
authors.lastname: Trainin
authors.forename: Irit
authors.initials: I
authors.lastname: Bar-Ya'akov
authors.forename: Hamutal
authors.initials: H
authors.lastname: Borochov-Neori
authors.forename: Doron
authors.initials: D
authors.lastname: Holland
mesh_terms: D016960:Agrobacterium tumefaciens / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D000872:Anthocyanins / Q000032:analysis / Q000096:biosynthesis* / Q000235:genetics; D017360:Arabidopsis / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics; D003001:Cloning, Molecular; D005638:Fruit / Q000235:genetics / Q000254:growth & development* / Q000502:physiology; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D005809:Genes, Regulator; D029561:Lythraceae / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism / Q000502:physiology; D008969:Molecular Sequence Data; D010641:Phenotype; D010858:Pigmentation; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D030821:Plants, Genetically Modified / Q000235:genetics / Q000254:growth & development / Q000378:metabolism / Q000502:physiology; D044945:Proanthocyanidins / Q000096:biosynthesis / Q000235:genetics; D011401:Promoter Regions, Genetic; D018749:RNA, Plant / Q000235:genetics*; D012639:Seeds / Q000235:genetics / Q000254:growth & development / Q000502:physiology; D016415:Sequence Alignment; D013997:Time Factors; D014170:Transformation, Genetic
chemical_list: D000872:Anthocyanins; D029681:Arabidopsis Proteins; D044945:Proanthocyanidins; D018749:RNA, Plant; C121067:TTG1 protein, Arabidopsis