Molecular Analysis of the anthocyanin2 Gene of Petunia and Its Role in the Evolution of Flower Color

Abstract

The shape and color of flowers are important for plant reproduction because they attract pollinators such as insects and birds. Therefore, it is thought that alterations in these traits may result in the attraction of different pollinators, genetic isolation, and ultimately, (sympatric) speciation. Petunia integrifolia and P. axillaris bear flowers with different shapes and colors that appear to be visited by different insects. The anthocyanin2 ( an2 ) locus, a regulator of the anthocyanin biosynthetic pathway, is the main determinant of color differences. Here, we report an analysis of molecular events at the an2 locus that occur during Petunia spp evolution. We isolated an2 by transposon tagging and found that it encodes a MYB domain protein, indicating that it is a transcription factor. Analysis of P. axillaris subspecies with white flowers showed that they contain an2 Ϫ alleles with two alternative frameshifts at one site, apparently caused by the insertion and subsequent excision of a transposon. A third an2 ؊ allele has a nonsense mutation elsewhere, indicating that it arose independently. The distribution of polymorphisms in an2 ؊ alleles suggests that the loss of an2 function and the consequent changes in floral color were not the primary cause for genetic separation of P. integrifolia and P. axillaris. Rather, they were events that occurred late in the speciation process, possibly to reinforce genetic isolation and complete speciation. INTRODUCTIONFlowers are the structures containing the male and female sex organs of angiosperms. Flowers of diverse species display a wide range of different morphologies and pollination strategies. For instance, flowers of wind-pollinated species usually possess small and inconspicuous petals or no petals at all, whereas flowers of insect-pollinated plants usually possess large, brightly colored, and patterned petals that serve as visual signals and a landing site for visiting insects.Recent experiments suggest that the wide variety of plant and flower morphologies may have depended on the evolution of a relatively small number of genes. First, mutations at single loci, usually isolated by breeders or researchers, are sufficient to cause fundamental alterations in inflorescence architecture (Doebley et al., 1997;Souer et al., 1998). Similarly, the different shapes, colors, and color patterns of naturally occurring Mimulus (monkeyflower) spp are due to alterations at only a few (major) loci (Bradshaw et al., 1995).Second, even very different inflorescence and flower architectures appear to be determined by genes that often encode conserved proteins but that differ in their expression patterns (reviewed in Doebley and Lukens, 1998).The isolation of key regulatory loci and analysis of the molecular alterations that have taken place in them will provide new insights into the evolution and diversification of flower morphology. The biosynthesis of anthocyanin flower pigments is particularly suited for such studies, because it is a well-defined biochemical pathway that is being...

Identification of major quantitative trait loci underlying floral pollination syndrome divergence in Penstemon

“…This QTL corresponds to the gene F3 0 5 0 h. Wessinger & Rausher [13] demonstrated using co-segregation and functional analyses that this gene is redundantly non-functional in P. barbatus and completely explains the difference in flower colour between the two species. Similar large effect flower colour QTLs have been reported frequently for adaptation to different pollinators between pairs of species within Aquilegia [35], Ipomopsis [15], Iris [14,17], Iochroma [36], Mimulus [9,37] and Petunia [10,18]. One partial explanation for this pattern is that many flower colour transitions involve deactivation of parts or all of the anthocyanin pathway, which can be accomplished by inactivating mutations in one or a few genes [10,13,36 -38].…”

“…Yet, some empirical evidence from quantitative trait locus (QTL) studies on pollination syndrome divergence suggests that there may be common patterns at the genetic level. For example, previous QTL studies have suggested that traits such as flower colour and nectar volume often involve few substitutions of medium to large effect [9][10][11][12][13], while changes in morphological characters tend to involve more loci with smaller effects [12,14,15]. In addition, these studies have revealed that QTLs for different traits sometimes co-localize (e.g.…”

Perianth colour affects germination behaviour in wind-pollinated Salsola rubescens in Arabian deserts

“…The shape and colour of flowers are important for plant sexual reproduction (Quattrocchio et al 1999). Flowers of diverse species display a wide range of different morphologies and pollination strategies.…”

“…Flowers of diverse species display a wide range of different morphologies and pollination strategies. For instance, windpollinated plants have small petals and inconspicuous colours or no petals at all, whereas animal-pollinated plants have developed display structures often characterized by brightly coloured and patterned petals that serve as visual signals and a landing site for visiting insects (Menzel and Shmida 1993;Quattrocchio et al 1999).…”

Inheritance and reproductive consequences of floral anthocyanin deficiency inSilene dioica (Caryophyllaceae)

“…Yet, natural plant populations often and persistently harbor rare fl ower color morphs that frequently include white morphs caused by mutations in biosynthetic pathways for fl oral pigments ( Quattrocchio et al, 1999 ;Schwinn et al, 2006 ;Streisfeld and Rausher, 2009 ). The most widely distributed fl oral pigments are anthocyanins that provide red to blue color to petals and are produced from the highly conserved fl avonoid biosynthetic pathway (reviewed in Grotewold, 2006 ).…”