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Tracing floral adaptations from ecology to molecules

Key Points

  • The study of floral evolution provides a simple system to investigate the link between environmental adaptation, phenotypic determination and genetic change.

  • The methods of molecular genetics offer powerful comparative tools for unravelling the evolution of floral adaptations.

  • Flower colour is a simple phenotype with well-characterized pathways of biochemical and molecular determination, which greatly facilitates comparative analysis.

  • The morning glory genus Ipomoea is well suited to comparative molecular research on floral evolution owing to the great range of floral phenotypes that have arisen in the genus in the past 30 million years.

  • Differences in floral colour among Ipomoea species seem to be largely the result of shifts in gene expression rather than the result of changes in enzymatic genes.

  • Over longer periods of evolutionary time (≥50 million years) gene duplication has been the source of important new innovations in the flavonoid biosynthesis.

  • Transposons are an important source of allelic diversity in flavonoid genes in Ipomoea species.

  • Ecological research with Ipomoea provides a direct link between phenotypic selection and the environment by showing that bumblebee pollinators discriminate between pigmented and white floral morphs, leading to asymmetries in genetic transmission that should favour white genes when they are expressed at low frequency.

  • The study of floral adaptation at all levels of biological organization requires mixing historical inference with direct experimentation.

Abstract

Flowers have long fascinated humans. The scientific study of floral biology unifies many diverse areas of research, ranging from systematics to ecology, and from genetics to molecular biology. Despite this unity, few plant species offer the experimental versatility to encompass all levels of biological investigation in a single system. An exception is the morning glory genus Ipomoea, in which a broad picture of floral evolution, ranging from ecology to molecular biology, is emerging.

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Figure 1: Between species and within species floral variation in Ipomoea.
Figure 2: Flavonoid biosynthetic pathway.
Figure 3: Differential patterns of expression of flavonoid genes in the petals of Ipomoea species.
Figure 4: Chalcone synthase gene family tree.
Figure 5: Transposon variation in chalcone synthase D sequences from Ipomoea purpurea and Ipomoea nil.

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Acknowledgements

This research was partially supported by a grant from the Alfred P. Sloan Foundation.

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Correspondence to Michael T. Clegg.

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Glossary

FLORAL TUBE

The tube-like, proximal-most region of Ipomoea petals.

FLORAL LIMB

The expanded, distal-most region of Ipomoea petals.

ANTHOCYANIN

Soluble glycoside pigments that produce the blue-to-red colour in flowers and other plant tissues.

MATING SYSTEM MODIFIER LOCI

Genes that alter the system of mating and the statistical rules of genetic transmission in populations. An example is a gene that increases the frequency of self-fertilization.

POLLEN DISCOUNTING

Situation in which the transmission of genes through pollen is reduced below a random expectation.

OVERDOMINANCE

Phenotypic expression is greater in the heterozygote than in either homozygote. This can result in an increased fitness of the heterozygote and lead to the maintenance of both alleles in the population.

PLEIOTROPIC

Responsible for several distinct and seemingly unrelated phenotypic effects.

FLAVONOID BIOSYNTHESIS

The production of a group of aromatic compounds that includes many common pigments such as flavones and anthocyanins.

TRANSPOSABLE ELEMENT

A segment of genetic material that is capable of changing its location in the genome of an organism.

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Clegg, M., Durbin, M. Tracing floral adaptations from ecology to molecules. Nat Rev Genet 4, 206–215 (2003). https://doi.org/10.1038/nrg1023

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