A Novel Chimeric Low-Molecular-Weight Glutenin Subunit Gene From the Wild Relatives of Wheat Aegilops kotschyi and Ae. juvenalis: Evolution at the Glu-3 Loci

Abstract

Four LMW-m and one novel chimeric (between LMW-i and LMW-m types) low-molecular-weight glutenin subunit (LMW-GS) genes from Aegilops neglecta (UUMM), Ae. kotschyi (UUSS), and Ae. juvenalis (DDMMUU) were isolated and characterized. Sequence structures showed that the 4 LMW-m-type genes, assigned to the M genome of Ae. neglecta, displayed a high homology with those from hexaploid common wheat. The novel chimeric gene, designed as AjkLMW-i, was isolated from both Ae. kotschyi and Ae. juvenalis and shown to be located on the U genome. Phylogentic analysis demonstrated that it had higher identity to the LMW-m-type than the LMW-i-type genes. A total of 20 single nucleotide polymorphisms (SNPs) were detected among the 4 LMW-m genes, with 13 of these being nonsynonymous SNPs that resulted in amino acid substitutions in the deduced mature proteins. Phylogenetic analysis demonstrated that it had higher identity to the LMW-m-type than the LMW-i-type genes. The divergence time estimation showed that the M and D genomes were closely related and diverged at 5.42 million years ago (MYA) while the differentiation between the U and A genomes was 6.82 MYA. We propose that, in addition to homologous recombination, an illegitimate recombination event on the U genome may have occurred 6.38 MYA and resulted in the generation of the chimeric gene AjkLMW-i, which may be an important genetic mechanism for the origin and evolution of LMW-GS Glu-3 alleles as well as other prolamin genes.

Phylogenetic analysis of C, M, N, and U genomes and their relationships with Triticum and other related genomes as revealed by LMW-GS genes at Glu-3 loci

“…Polymerase chain reaction (PCR) amplifications were based on Li et al (2008aLi et al ( , 2008b. Two pairs of allelic-specific polymerase chain reaction (AS-PCR) primers (LMW-1 and LMW-2, and LMW-7 and LMW-8) were used to amplify LMW-GS genes ( Table 2) 2) as described by Pei et al (2007) and Jiang et al (2008).…”

“…Wheat storage proteins, which are closely associated with bread-making quality, have shown to be effective genetic markers for studying phylogenetic and evolutionary relationships among Triticum and Aegilops genomes Zhang et al 2008;Li et al , 2008aLi et al , 2008bLi et al , 2010. The low-molecular-weight glutenin subunits (LMW-GS), a main class of seed storage proteins, are encoded by multigenic families at Glu-A3, Glu-B3, and Glu-D3 loci on the short arms of chromosomes 1A, 1B, and 1D, respectively (Payne 1987).…”

Novel LMW glutenin subunit genes from wild emmer wheat (Triticum turgidum ssp. dicoccoides) in relation to Glu-3 evolution

“…In addition, one HMW-GS y-/x-type chimeric gene was characterized from Aegilops searsii (Sun et al 2006). Novel chimeric genes (between LMW-i-and LMW-m-type LMW-GSs) were isolated from both Aegilops kotschyi and Aegilops juvenalis (Li et al 2008a). Chimeric HMW-GS genes were also found to generate through illegitimate recombination in wheat-rye hybrids and even somatic hybrids between wheat and tall wheatgrass (Liu et al 2007;Yuan et al 2011).…”

Characterization of low-molecular-weight glutenin subunit genes of Aegilops section Sitopsis and comparative analysis with those of wheat (Triticum aestivum L.) and some Aegilops species

“…It not only contributes the entire D genome of wheat, but also has been proposed as B genome ancestor. Consequently, extensive studies on novel LMW-GS gene mining have also been conducted in Aegilops genus, such as species containing D, C, M, N, U genomes (Ciaffi et al 1999;Gianibelli et al 2002;Johal et al 2004;Huang et al 2005;Wang et al 2011;Li et al 2008Li et al , 2010. However, little information is available about the LMW-GS genes in Sitopsis section, the putative B genome donor of wheat.…”