Rapid changes of microsatellite flanking sequence in the allopolyploidization of new synthesized hexaploid wheat

Abstract

It was suggested that the rapid changes of DNA sequence and gene expression occurred at the early stages of allopolyploid formation. In this study, we revealed the microsatellite (SSR) differences between newly formed allopolyploids and their donor parents by using 21 primer sets specific for D genome of wheat. It was indicated that rapid changes had occurred in the "shock" process of the allopolyploid formation between tetraploid wheat and Aegilops tauschii. The changes of SSR flanking sequence resulted in appearance of novel bands or disappearance of parental bands. The disappearance of the parental bands showed much higher frequencies in comparison with that of appearance of novel bands. Disappearance of the parental bands was not random. The frequency of disappearance in tetraploid wheat was much higher than in Ae. tauschii, i. e. the disappearance frequency in AABB genome was much higher than in D genome. Changes of SSR flanking sequence occurred at the early stage of F1 hybrid or just after chromosome doubling. From the above results, it can be inferred that SSR flanking sequence region was very active and was amenable to change in the process of polyploidization. This suggested that SSR flanking sequence probably had special biological function at the early stage of ployploidization. The rapid and directional changes at the early stage of polyploidization might contribute to the rapid evolution of the newly formed allopolyploid and allow the divergent genomes to act in harmony.

Molecular and Phenotypic Characterization of Advanced Backcross Lines Derived from Interspecific Hybridization of Durum Wheat

“…In our study primer pairs specific for the B and D genome SSR loci amplified in T. timopheevii, the tetraploid donor of the AG genome (7/33 = 21.2 %). Similarly, primer pairs for some SSR loci located on the D genome of common wheat amplified tetraploid species with AABB genomes: T. cartlicum (6/33 = 18.2 %), T. dicoccoides (2/33 = 6.1 %), T. dicoccum (2/33 = 6.1 %) and T. polonicum (1/33 = 3 %) as has been shown for T. urartu (donor of the wheat A genome) or Aegilops speltoides or its related species (the probable donor of the wheat B genome) (94). Among the SSR markers mapped on the D genome, only Xgwm 642-1D showed amplification in the genome of cultivated wheat cvs.…”

“…tauschii) with 21 D-genome specific primers and a primer set of 66 SSRs specific to the A/B genomes of common wheat showed that some primer pairs specific to the D genome of wheat could amplify SSR products in tetraploid wheat with AABB genomes and over 70 % of A/B genome specific SSR markers could amplify SSR products in Ae. tauschii with the D genome (94,95). These reports drew attention to the fact that some amplification products in tetraploid wheat disappeared in the synthesized hexaploid wheat background and emphasized on the difficulty of determining the origin (from the D genome or from A/B genomes) of some amplified SSR fragments in synthetic hexaploid wheat.…”

“…Other studies involving artificially synthesized allopolyploids of Triticeae revealed allopolyploidization-induced, rapid DNA sequence changes (including also DNA elimination) in new synthetic allopolyploids. However, several reports (26,27,72) suggest that the locus specificity of SSRs in common wheat is most probably due to mutations in primer binding sites, rather than to loss of SSRs themselves in related genomes during polyploidization events (94,95). The above-mentioned observations suggested that caution should be taken when using SSR markers to genotype new synthetic hexaploid wheat or other interspecific wheat hybrids (95).…”

Empirical verification of heterogeneous DNA fragments generated from wheat genome-specific SSR primers

“…The molecular genetic maps of common wheat contain over 1500 SSRs, some of them were mapped to single locus and specific to individual chromosome or chromosome arm (Bryan et al 1997;Ro¨der et al 1998Ro¨der et al , 2004Pestsova et al 2000;Somers et al 2004). SSRs from common wheat have been shown to give amplification in many related or alien species and vice versa, which is known as ''transferability'' (Pestova et al 2000;Sourdille et al 2001;Guyomarc'h et al 2002a,b;Sharma et al 2002;Kuleung et al 2004;Adonina et al 2005;Zhang et al 2004Zhang et al , 2005Zhang et al , 2007a. Comparison of SSR patterns among newly synthesized hexaploid wheat (SHW) and its donor T. turgidum and Ae.…”

“…These results suggested that these SSR markers specific to D genome in common wheat were probably nonspecific to D genome in SHWs. Similarly, some SSR primers specific to A/B genome in common wheat were probably nonspecific to the A/B genome in SHWs (Zhang et al 2004(Zhang et al , 2007a. Given that the wheat genome is so large and complex, it can be hypothesized that the chance of amplifying non-specific sequences is very high.…”