title: Precise spatio-temporal regulation of the anthocyanin biosynthetic pathway leads to petal spot formation in Clarkia gracilis (Onagraceae).
abstract: Petal spots are widespread in angiosperms and are often implicated in pollinator attraction. Clarkia gracilis petals each have a single red-purple spot that contrasts against a pink background. The position and presence of spots in C. gracilis are determined by the epistatic interaction of alleles at two as yet unidentified loci. We used HPLC to identify the different pigments produced in the petals, and qualitative and quantitative RT-PCR to assay for spatio-temporal patterns of expression of different anthocyanin pathway genes. We found that spots contain different pigments from the remainder of the petal, being composed of cyanidin/peonidin-based, instead of malvidin-based anthocyanins. Expression assays of anthocyanin pathway genes showed that the dihydroflavonol-4-reductase 2 (Dfr2) gene has a spot-specific expression pattern and acts as a switch for spot production. Co-segregation analyses implicated the gene products of the P and I loci as trans-regulators of this switch. Spot pigments appear earlier in development as a result of early expression of Dfr2 and the flavonoid 3' hydroxylase 1 (F3'h1) gene. Pigments in the background appear later, as a result of later expression of Dfr1 and the flavonoid 3'-5' hydroxylase 1 (F3'5'h1) genes. The evolution of this spot production mechanism appears to have been facilitated by duplication of the Dfr gene and to have required substantial reworking of the anthocyanin pathway regulatory network.
authors.affiliation: Department of Botany, University of Wisconsin, Madison, WI, 53706, USA.|Department of Biology, Duke University, Durham, NC, 27708, USA.
authors.forename: Talline R
authors.initials: TR
authors.lastname: Martins
authors.affiliation: Department of Botany, University of Wisconsin, Madison, WI, 53706, USA.
authors.forename: Jeremy J
authors.initials: JJ
authors.lastname: Berg
authors.affiliation: Department of Botany, University of Wisconsin, Madison, WI, 53706, USA.
authors.forename: Steven
authors.initials: S
authors.lastname: Blinka
authors.affiliation: Department of Biology, Duke University, Durham, NC, 27708, USA.
authors.forename: Mark D
authors.initials: MD
authors.lastname: Rausher
authors.affiliation: Department of Botany, University of Wisconsin, Madison, WI, 53706, USA.
authors.forename: David A
authors.initials: DA
authors.lastname: Baum
mesh_terms: D000872:Anthocyanins / Q000096:biosynthesis* / Q000235:genetics; D002851:Chromatography, High Pressure Liquid; D003433:Crosses, Genetic; D018744:DNA, Plant / Q000737:chemistry; D035264:Flowers / Q000033:anatomy & histology / Q000254:growth & development / Q000378:metabolism; D005838:Genotype; D029594:Onagraceae / Q000033:anatomy & histology / Q000254:growth & development / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA
chemical_list: D000872:Anthocyanins; D018744:DNA, Plant; D012333:RNA, Messenger