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Global transgenerational gene expression dynamics in two nascent allohexaploid wheat lines analogous in genome constitution to common wheat (Triticum aestivum)

ABSTRACT: Alteration in gene expression accompanying initial stages of allopolyploidy is a prominent feature in plants, but its spectrum and model are highly idiosyncratic. We used multi-colour GISH to identify individuals from two nascent allohexaploid wheat lines between Triticum turgidum and Aegilops tauschii, which had a transgenerationally stable chromosomal constitution mimicking that of common wheat. We performed genomewide analysis of gene expression for these plants along with their parental species using the Affymetrix GeneChip Wheat Genome-Array. Comparison with parental species coupled with inclusion of empirical mid-parent values (MPVs) revealed two patterns of alteration in gene expression in the allohexaploid lines: parental dominance expression and nonadditive expression. Genes involved in each altered pattern could be classified into three distinct groups, stochastic, heritable and persistent, based on their transgenerational heritability and inter-line conservation. Whereas both altered patterns of gene expression showed a propensity of inheritance, identity of the involved genes is stochastic, consistent with the involvement of diverse Gene Ontology (GO) terms. Nonetheless, those genes showing nonadditive expression exhibited a significant enrichment for vesicle-function. Our results suggest global alteration in gene expression conditioned by nascent allopolyploidy likely play functional roles in stabilization and establishment of the newly formed plants, and consequential to evolution.

ORGANISM(S): Aegilops tauschii Triticum carthlicum Triticum aestivum Triticum turgidum subsp. durum

PROVIDER: GSE29882 | GEO | 2012/05/01

SECONDARY ACCESSION(S): PRJNA140735

REPOSITORIES: GEO

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Project description:The three subgenomes (B, A and D) of common wheat (2n=6x=42) are largely intact, which makes extraction of the BBAA subgenomes as organismally independent genomes possible. Availability of such novel extracted tetraploid wheat (Extracted-tetra) provides a unique opportunity to study whether and to what extent the BBAA subgenomes of common wheat have been irreversibly modified, as well as its attendant biological consequences, during their evolutionary trajectory as allohexaploidy. We report here that the extracted-tetra is stable in karyotype but with severely deteriorated phenotypes. Microarray-based transcriptome analysis revealed a substantial portion of differentially expressed genes (down- or up-regulation) between extracted and natural tetraploid wheat, Triticum turgidum, which exceeded the transcriptome divergence at tetraploid level, implying reinforced effects of allopolyploidization and domestication at the allohexaploid level. Great majority of the differentially expressed genes showed additive expression in a resynthesized allohexaploid wheat (parented by Extracted-tetra), indicating transcriptome modifications to the BBAA subgenomes are largely irreversible. Analysis of a newly synthesized allohexaploid wheat (parented by T. turgidum) suggests that whereas most of the modified genes are accrued evolutionary changes, some showed immediate regulation post-allohexaploidization and evolutionary perseverance. Homeologue-specific pyrosequencing of 44 genes revealed either concordant or independent expression changes to the B and A homeologues. The Extracted-tetra vs.T. turgidum down-regulated genes showed enrichment for distinct GO categories. Structurally, the three constituent subgenomes of common wheat, BB, AA and DD, are largely intact with only a few inter-subgenomic translocations. Because of these unique attributes, it is feasible to extract the BBAA subgenomes from the common wheat BBAADD genome by hybridization to a durum line and repeated back-crossing to the hexaploid parent, restituting a novel type of extracted tetraploid wheat, namely Extracted-tetr, with a genome constitution BBAA, virtually identical to the subgenomes BBAA of its common wheat donor. Availability of the extracted-tetra, the resynthesized allohexaploid wheat parented by the extracted-tetra, and newly synthesized allohexaploid wheat parented by natural tetraploid wheat, T. turgidum, provides an excellent system to address the issues of whether and to what extent transcriptome modifications to the BBAA subgenomes of common wheat have occurred since its formation ca. 10,000 years ago, timing of the modifications, and their biological consequences. Here, we have addressed these issues by microarray-based transcriptome analysis.

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Global transgenerational gene expression dynamics in two nascent allohexaploid wheat lines analogous in genome constitution to common wheat (Triticum aestivum)

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