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Competition between anthocyanin and flavonol biosynthesis produces spatial pattern variation of floral pigments between Mimulus species.

ABSTRACT: Flower color patterns have long served as a model for developmental genetics because pigment phenotypes are visually striking, yet generally not required for plant viability, facilitating the genetic analysis of color and pattern mutants. The evolution of novel flower colors and patterns has played a key role in the adaptive radiation of flowering plants via their specialized interactions with different pollinator guilds (e.g., bees, butterflies, birds), motivating the search for allelic differences affecting flower color pattern in closely related plant species with different pollinators. We have identified LIGHT AREAS1 (LAR1), encoding an R2R3-MYB transcription factor, as the causal gene underlying the spatial pattern variation of floral anthocyanin pigmentation between two sister species of monkeyflower: the bumblebee-pollinated Mimulus lewisii and the hummingbird-pollinated Mimulus cardinalis. We demonstrated that LAR1 positively regulates FLAVONOL SYNTHASE (FLS), essentially eliminating anthocyanin biosynthesis in the white region (i.e., light areas) around the corolla throat of M. lewisii flowers by diverting dihydroflavonol into flavonol biosynthesis from the anthocyanin pigment pathway. FLS is preferentially expressed in the light areas of the M. lewisii flower, thus prepatterning the corolla. LAR1 expression in M. cardinalis flowers is much lower than in M. lewisii, explaining the unpatterned phenotype and recessive inheritance of the M. cardinalis allele. Furthermore, our gene-expression analysis and genetic mapping results suggest that cis-regulatory change at the LAR1 gene played a critical role in the evolution of different pigmentation patterns between the two species.

SUBMITTER: Yuan YW

PROVIDER: S-EPMC4780602 | biostudies-literature | 2016 Mar

REPOSITORIES: biostudies-literature

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Competition between anthocyanin and flavonol biosynthesis produces spatial pattern variation of floral pigments between Mimulus species.

Yuan Yao-Wu YW Rebocho Alexandra B AB Sagawa Janelle M JM Stanley Lauren E LE Bradshaw Harvey D HD

Proceedings of the National Academy of Sciences of the United States of America 20160216 9

Flower color patterns have long served as a model for developmental genetics because pigment phenotypes are visually striking, yet generally not required for plant viability, facilitating the genetic analysis of color and pattern mutants. The evolution of novel flower colors and patterns has played a key role in the adaptive radiation of flowering plants via their specialized interactions with different pollinator guilds (e.g., bees, butterflies, birds), motivating the search for allelic differe ...[more]

PMID: 26884205

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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.

Dataset Information

Competition between anthocyanin and flavonol biosynthesis produces spatial pattern variation of floral pigments between Mimulus species.

Publications

Competition between anthocyanin and flavonol biosynthesis produces spatial pattern variation of floral pigments between Mimulus species.

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