Sequence Polymorphism in Polyploid Wheat and Their D-Genome Diploid Ancestor

Abstract

Sequencing was used to investigate the origin of the D genome of the allopolyploid species Triticum aestivum and Aegilops cylindrica. A 247-bp region of the wheat D-genome Xwye838 locus, encoding ADPglucopyrophosphorylase, and a 326-bp region of the wheat D-genome Gss locus, encoding granule-bound starch synthase, were sequenced in a total 564 lines of hexaploid wheat (T. aestivum, genome AABBDD) involving all its subspecies and 203 lines of Aegilops tauschii, the diploid source of the wheat D genome. In Ae. tauschii, two SNP variants were detected at the Xwye838 locus and 11 haplotypes at the Gss locus. Two haplotypes with contrasting frequencies were found at each locus in wheat. Both wheat Xwye838 variants, but only one of the Gss haplotypes seen in wheat, were found among the Ae. tauschii lines. The other wheat Gss haplotype was not found in either Ae. tauschii or 70 lines of tetraploid Ae. cylindrica (genomes CCDD), which is known to hybridize with wheat. It is concluded that both T. aestivum and Ae. cylindrica originated recurrently, with at least two genetically distinct progenitors contributing to the formation of the D genome in both species.

Single-copy gene fluorescence in situ hybridization and genome analysis: Acc-2 loci mark evolutionary chromosomal rearrangements in wheat

“…Thus, the total number of undetected Acc-2 gene or pseudogene copies may even be higher. In polyploid species, the PCR cloning approach and Southern hybridization analysis may not detect copies of homoeologous or orthologous genes because of sequence divergence or high sequence identity (Feuillet et al 2001;Huang et al 2002;Caldwell et al 2004). FISH can help in mapping and evaluating the copy number of these genes.…”

Repeated Polyploidy Drove Different Levels of Crossover Suppression between Homoeologous Chromosomes inBrassica napusAllohaploids

“…Common bread wheat (Triticum aestivum; 2n = 6x = 42; genome formula AABBDD) is the product of two successive polyploidization events (2x/4x then 4x/6x); it arose from at least two maternal lineages (Hirosawa et al, 2004), had two genetically distinct D-genome progenitors (Caldwell et al, 2004), and captured a large portion of the natural genetic diversity present in its tetraploid ancestor (Dubcovsky and Dvorak, 2007). In both tetraploid and hexaploid wheat, the main locus responsible for exclusive homologous CO formation is Ph1 (Riley and Chapman, 1958;Feldman, 1966;Sears, 1976;Giorgi, 1978), which was recently defined to a region containing a cluster of cyclin-dependent kinase-related genes interrupted by a heterochromatin segment (Griffiths et al, 2006;Al-Kaff et al, 2008).…”

The time lag between introduction and escape from cultivation of alien woody plant species decreases with polyploidization

“…However, there is only limited empirical support for the hypothesis that the evolutionary rates differ between polyploids and diploids (Soltis et al, 2003b). While some studies reported an increase in the ratio of non-synonymous to synonymous nucleotide substitutions or higher nucleotide diversity in polyploids (Sun et al, 2007), others found the opposite pattern (Caldwell et al, 2004) or no difference (Cedroni et al, 2003). This suggests that the success of polyploids is not the result of the accumulation of mutations in non-functional genes that become functional within a new environment.…”