Ancestors of white clover (Trifolium repens L.), as revealed by isozyme polymorphisms

Badr, Abdelfattah; Sayed-Ahmed, H.; El-Shanshouri, A.R.; Watson, Linda E.

doi:10.1007/s00122-002-1010-5

Cited by 32 publications

(31 citation statements)

References 27 publications

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“…White clover is thought to have originated through the hybridization of a cyanogenic species (contributing Ac and Li) and an acyanogenic species (possessing neither gene) (Williams and Williamson 2001;Badr et al 2002). One of the hallmarks of allopolyploidization is the rapid and widespread elimination of genomic sequences in the immediate aftermath of the hybridization event (e.g., Feldman et al 1997;Ozkan et al 2001; reviewed by Ma and Gustafson 2005).…”

Section: Discussionmentioning

confidence: 99%

“…Chromosome number and genetic map data indicate that white clover is an allotetraploid (e.g., Barrett et al 2004). While Ac and Li have not been mapped, both cyanogenesis genes are believed to be present in only one of the two parental genomes (e.g., Williams and Williamson 2001); this suggests that the species originated through the hybridization of a cyanogenic and an acyanogenic Trifolium species (Williams and Williamson 2001;Badr et al 2002).The ecological genetics of white clover cyanogenesis has been studied for .60 years, and this system represents one of the best-documented examples of an adaptive polymorphism in plants (reviews by Hughes 1991; Hayden and Parker 2002;Olsen et al 2007). Cyanogenic plants are generally found to be strongly favored in the presence of generalist herbivores, which avoid eating them (e.g., Ennos 1981; Dirzo and Harper 1982a,b;Pederson and Brink 1998;Saucy et al 1999;Viette et al 2000).…”

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Evidence on the Molecular Basis of the Ac/ac Adaptive Cyanogenesis Polymorphism in White Clover (Trifolium repens L.)

2008

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White clover is polymorphic for cyanogenesis, with both cyanogenic and acyanogenic plants occurring in nature. This chemical defense polymorphism is one of the longest-studied and best-documented examples of an adaptive polymorphism in plants. It is controlled by two independently segregating genes: Ac/ac controls the presence/absence of cyanogenic glucosides; and Li/li controls the presence/absence of their hydrolyzing enzyme, linamarase. Whereas Li is well characterized at the molecular level, Ac has remained unidentified. Here we report evidence that Ac corresponds to a gene encoding a cytochrome P450 of the CYP79D protein subfamily (CYP79D15), and we describe the apparent molecular basis of the Ac/ac polymorphism. CYP79D orthologs catalyze the first step in cyanogenic glucoside biosynthesis in other cyanogenic plant species. In white clover, Southern hybridizations indicate that CYP79D15 occurs as a single-copy gene in cyanogenic plants but is absent from the genomes of ac plants. Gene-expression analyses by RT-PCR corroborate this finding. This apparent molecular basis of the Ac/ac polymorphism parallels our previous findings for the Li/li polymorphism, which also arises through the presence/ absence of a single-copy gene. The nature of these polymorphisms may reflect white clover's evolutionary origin as an allotetraploid derived from cyanogenic and acyanogenic diploid progenitors. C YANOGENESIS (cyanide release following tissue damage) occurs in .2650 plant species, including ferns, gymnosperms, monocots, and dicots (Seigler and Brinker 1993). In its most common form, cyanogenesis involves the interaction of two compounds, cyanogenic glycosides and their hydrolyzing enzymes; these are separated in intact tissue and brought into contact with tissue disruption. White clover (Trifolium repens L., Fabaceae) is polymorphic for cyanogenesis, with both cyanogenic and acyanogenic plants occurring in natural populations (Armstrong et al. 1913;Ware 1925). This polymorphism arises through the presence/absence of both of the underlying cyanogenic components. Inheritance of cyanogenesis in white clover follows a simple Mendelian two-locus, two-allele model (Coop 1940;Melville and Doak 1940;Corkill 1942): the gene Ac/ac controls the presence/absence of cyanogenic glucosides; and the independently segregating gene Li/li controls the presence/absence of linamarase, a cyanogenic b-glucosidase (reviewed by Hughes 1991). Plants that carry at least one dominant (functional) allele at both genes (Ac and Li) are cyanogenic, while the occurrence of two nonfunctional alleles at either gene confers the acyanogenic phenotype.White clover is a common legume of fields, lawns, and pastures in mesic temperate climates. It is a native of Eurasia but has been introduced worldwide as a forage crop and lawn plant. It is a perennial and an insectpollinated, obligate outcrosser; plants also spread vegetatively by stolons. Chromosome number and genetic map data indicate that white clover is an allotetraploid (e.g., Barrett et al. 200...

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Section: Discussionmentioning

confidence: 99%

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confidence: 99%

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Evidence on the Molecular Basis of the Ac/ac Adaptive Cyanogenesis Polymorphism in White Clover (Trifolium repens L.)

2008

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“…Three species in the clade are known to be polyploid (T. ambiguum, T. repens and T. uniflorum). In the case of white clover, which is allotetraploid, the Ac and Li genes occur within only one of its two parental genomes, suggesting that this species may have originated through the hybridization of a cyanogenic and an acyanogenic diploid progenitor [39,45]. Proposed progenitors within Trifoliastrum have included T. occidentale, T. nigrescens ssp.…”

Section: Materials and Methods (A) Samplingmentioning

confidence: 99%

“…Proposed progenitors within Trifoliastrum have included T. occidentale, T. nigrescens ssp. petrisavii, T. pallescens and an unknown lineage [37,39,45,46].…”

Section: Materials and Methods (A) Samplingmentioning

confidence: 99%

Adaptive gains through repeated gene loss: parallel evolution of cyanogenesis polymorphisms in the genusTrifolium(Fabaceae)

Olsen

Kooyers

Small

2014

Phil. Trans. R. Soc. B

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Variation in cyanogenesis (hydrogen cyanide release following tissue damage) was first noted in populations of white clover more than a century ago, and subsequent decades of research have established this system as a classic example of an adaptive chemical defence polymorphism. Here, we document polymorphisms for cyanogenic components in several relatives of white clover, and we determine the molecular basis of this trans-specific adaptive variation. One hundred and thirty-nine plants, representing 13 of the 14 species within Trifolium section Trifoliastrum , plus additional species across the genus, were assayed for cyanogenic components (cyanogenic glucosides and their hydrolysing enzyme, linamarase) and for the presence of underlying cyanogenesis genes ( CYP79D15 and Li , respectively). One or both cyanogenic components were detected in seven species, all within section Trifoliastrum ; polymorphisms for the presence/absence (PA) of components were detected in six species. In a pattern that parallels our previous findings for white clover, all observed biochemical polymorphisms correspond to gene PA polymorphisms at CYP79D15 and Li . Relationships of DNA sequence haplotypes at the cyanogenesis loci and flanking genomic regions suggest independent evolution of gene deletions within species. This study thus provides evidence for the parallel evolution of adaptive biochemical polymorphisms through recurrent gene deletions in multiple species.

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Hybridisation ‐ Reproductive Barriers to Gene Flow

Richard¹

2005

Gene Flow From GM Plants

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Ancestors of white clover (Trifolium repens L.), as revealed by isozyme polymorphisms

Cited by 32 publications

References 27 publications

Evidence on the Molecular Basis of the Ac/ac Adaptive Cyanogenesis Polymorphism in White Clover (Trifolium repens L.)

Evidence on the Molecular Basis of the Ac/ac Adaptive Cyanogenesis Polymorphism in White Clover (Trifolium repens L.)

Adaptive gains through repeated gene loss: parallel evolution of cyanogenesis polymorphisms in the genusTrifolium(Fabaceae)

Hybridisation ‐ Reproductive Barriers to Gene Flow

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