The Capacity to Buffer and Sustain Imbalanced D-Subgenome Chromosomes by the BBAA Component of Hexaploid Wheat Is an Evolved Dominant Trait.

Xin Deng,Zhenling Lv,Ai Zhang,Yan Sha,Ying Wu,Bao Liu,Fang Wang

doi:10.3389/fpls.2018.01149

Xin Deng, Zhenling Lv + Show 5 more

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https://doi.org/10.3389/fpls.2018.01149

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Abstract

Successful generation of pentaploid wheat (genome, BBAAD) via interspecific hybridization between tetraploid wheat (BBAA) and hexaploid wheat (BBAADD) holds great promise to mutually exchange desirable traits between the two cultivated wheat species, as well as providing a novel facet for evolutionary studies of polyploid wheat. Taking advantage of the viable and fertile nature of an extracted tetraploid wheat (ETW) with a BBAA genome that is virtually identical with the BBAA component of a hexaploid common wheat, and a synthetic hexaploid wheat, we constructed four pentaploid wheats with several distinct yet complementary features, of which harboring homozygous BBAA subgenomes is a common feature. By using a combined FISH/GISH method that enables diagnosing all individual wheat chromosomes, we precisely karyotyped a larger number of cohorts from the immediate progenies of each of the four pentaploid wheats. We found that the BBAA component of hexaploid common wheat possesses a significantly stronger capacity to buffer and sustain imbalanced D genome chromosomes and appears to harbor more structural chromosome variations than the BBAA genome of tetraploid wheat. We also document that this stronger capacity of the hexaploid BBAA subgenomes behaves as a genetically controlled dominant trait. Our findings bear implications to the known greater than expected level of genetic diversity in, and the remarkable adaptability of, hexaploid common wheat as a staple crop of global significance, as well as in using pentaploidy as intermediates for reciprocal introgression of useful traits between tetraploid and hexaploid wheat cultivars.

Highlights

Aneuploidy, with losses and/or gains of individual chromosomes, and deviating from the default balanced chromosome complement(s) of any species, is a large-effect genetic variant with profound biological consequences
We have shown in this study that all three manifestations, i.e., overall chromosome number distribution/exact chromosome composition, NCVs, and SCVs, are strikingly different between the immediate progenies of a pentaploid wheat (ST) with the BBAA genome of a tetraploid durum wheat
Given the common feature of these three pentaploid wheat lines, i.e., all harboring homozygous BBAA subgenomes (Figure 1A), our results have unequivocally shown that the BBAA component of a hexaploid wheat possess a greater capacity than the BBAA genome of a durum wheat to buffer and sustain unbalanced D chromosomes, and to constitute more kinds, more complex, greater severity of aneuploidies, as well as higher levels of SCVs in the progeny cohorts of the corresponding pentaploid wheats constituted by the former than that by the later

Summary

Introduction

Aneuploidy, with losses and/or gains of individual chromosomes, and deviating from the default balanced chromosome complement(s) of any species, is a large-effect genetic variant with profound biological consequences. Recent studies have documented that aneuploidy is common and often persistent (rather than transit as commonly thought) in newly formed plant polyploids (Xiong et al, 2011; Chester et al, 2012; Zhang et al, 2013), which has led to the suggestion that numerical chromosome changes (aneuploidy) may have played a protracted role at the initial stages of polyploid establishment, adaptation, and evolution (Soltis et al, 2015) This possibility is bolstered by the observation that many types of aneuploidy are reversible in the sense that euploidy progenitors can be readily generated from aneuploid progenitors, which may retain some of the desirable properties of the aneuploid progenitors (Henry et al, 2010). This is consistent with our recent observation that aneuploidy-induced epigenetic modifications in the form of altered DNA methylation were imparted to the aneuploidyderived euploid progenies at appreciable frequencies (Gao et al, 2016)

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