Dataset Information

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.

SUBMITTER: Martins TR

PROVIDER: S-EPMC3540125 | biostudies-literature | 2013 Feb

REPOSITORIES: biostudies-literature

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Precise spatio-temporal regulation of the anthocyanin biosynthetic pathway leads to petal spot formation in Clarkia gracilis (Onagraceae).

Martins Talline R TR Berg Jeremy J JJ Blinka Steven S Rausher Mark D MD Baum David A DA

The New phytologist 20121210 3

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 d ...[more]

PMID: 23231386

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Project description:Given that flower size and pigmentation can mediate plant-pollinator interactions, many studies have focused on pollinator-driven selection on these floral traits. However, abiotic factors such as precipitation, temperature, and solar radiation also contribute to geographic variation in floral color, pattern, and size within multiple species. Several studies have described an ecogeographic pattern within species in which high temperature, high ultraviolet (UV) radiation, low precipitation and/or low latitudes are associated with increased floral anthocyanin production, smaller flowers, and/or larger UV-absorbing floral patterns (nectar guides or bullseyes). However, latitude or elevation is often used as a proxy variable to study variation in floral traits associated with a wide range of climatic variables, making the proximate abiotic drivers of variation difficult to identify. In this study, we tested and corroborated several predictions for how the abiotic environment may directly or indirectly shape geographic patterns of floral color, pattern, and size in Clarkia unguiculata (Onagraceae). This study provides the first report of geographic variation in multispectral floral color and pattern in C. unguiculata, while also providing an experimental test of the putative protective role of UV absorption for pollen performance. We quantified geographic variation among greenhouse-raised populations in UV floral pattern size, mean UV petal reflectance, anthocyanin concentration, and petal area in C. unguiculata across its natural range in California and, using 30 year climate normals for each population, we identified climatic and topographic attributes that are correlated with our focal floral traits. In addition, we examined pollen performance under high and low UV light conditions to detect the protective function (if any) of UV floral patterns in this species. Contrary to our expectations, the nectar guide and the proportion of the petal occupied by the UV nectar guide were largest in low solar UV populations. Estimated floral anthocyanin concentration was highest in populations with high solar UV, which does support our predictions. The size of the UV nectar guide did not affect pollen performance in either of the light treatments used in this study. We conclude that, under the conditions examined here, UV-absorbing floral patterns do not serve a direct "pollen protection" function in C. unguiculata. Our results only partially align with expected ecogeographic patterns in these floral traits, highlighting the need for research in a wider range of taxa in order to detect and interpret broad scale patterns of floral color variation.

Project description:BACKGROUND:Anthocyanins are the primary source of colour in flowers and also accumulate in vegetative tissues, where they have multiple protective roles traditionally attributed to early compounds of the metabolic pathway (flavonols, flavones, etc.). Petal-specific loss of anthocyanins in petals allows plants to escape from the negative pleiotropic effects of flavonoid and anthocyanins loss in vegetative organs, where they perform a plethora of essential functions. Herein, we investigate the degree of pleiotropy at the biochemical scale in a pink-white flower colour polymorphism in the shore campion, Silene littorea. We report the frequencies of pink and white individuals across 21 populations and underlying biochemical profiles of three flower colour variants: anthocyanins present in all tissues (pink petals), petal-specific loss of anthocyanins (white petals), and loss of anthocyanins in all tissues (white petals). RESULTS:Individuals lacking anthocyanins only in petals represent a stable polymorphism in two populations at the northern edge of the species range (mean frequency 8-21%). Whereas, individuals lacking anthocyanins in the whole plant were found across the species range, yet always at very low frequencies (<?1%). Biochemically, the flavonoids detected were anthocyanins and flavones; in pigmented individuals, concentrations of flavones were 14-56× higher than anthocyanins across tissues with differences of >?100× detected in leaves. Loss of anthocyanin pigmentation, either in petals or in the whole plant, does not influence the ability of these phenotypes to synthesize flavones, and this pattern was congruent among all sampled populations. CONCLUSIONS:We found that all colour variants showed similar flavone profiles, either in petals or in the whole plant, and only the flower colour variant with anthocyanins in photosynthetic tissues persists as a stable flower colour polymorphism. These findings suggest that anthocyanins in photosynthetic tissues, not flavonoid intermediates, are the targets of non-pollinator mediated selection.

Project description:Angiosperms are renown for their diversity of flower colors. Often considered adaptations to pollinators, the most common underlying pigments, anthocyanins, are also involved in plants' stress response. Although the anthocyanin biosynthetic pathway is well characterized across many angiosperms and is composed of a few candidate genes, the consequences of blocking this pathway and producing white flowers has not been investigated at the transcriptome scale. We take a transcriptome-wide approach to compare expression differences between purple and white petal buds in the arctic mustard, Parrya nudicaulis, to determine which genes' expression are consistently correlated with flower color. Using mRNA-Seq and de novo transcriptome assembly, we assembled an average of 722 bp per gene (49.81% coding sequence based on the A. thaliana homolog) for 12,795 genes from the petal buds of a pair of purple and white samples. Our results correlate strongly with qRT-PCR analysis of nine candidate genes in the anthocyanin biosynthetic pathway where chalcone synthase has the greatest difference in expression between color morphs (P/W = ∼7×). Among the most consistently differentially expressed genes between purple and white samples, we found 3× more genes with higher expression in white petals than in purple petals. These include four unknown genes, two drought-response genes (CDSP32, ERD5), a cold-response gene (GR-RBP2), and a pathogen defense gene (DND1). Gene ontology analysis of the top 2% of genes with greater expression in white relative to purple petals revealed enrichment in genes associated with stress responses including cold, drought and pathogen defense. Unlike the uniform downregulation of chalcone synthase that may be directly involved in the loss of petal anthocyanins, the variable expression of several genes with greater expression in white petals suggest that the physiological and ecological consequences of having white petals may be microenvironment-dependent.

Dataset Information

Precise spatio-temporal regulation of the anthocyanin biosynthetic pathway leads to petal spot formation in Clarkia gracilis (Onagraceae).

Publications

Precise spatio-temporal regulation of the anthocyanin biosynthetic pathway leads to petal spot formation in Clarkia gracilis (Onagraceae).

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