Chromosome Stability of Synthetic-Natural Wheat Hybrids

Abstract

Primary allopolyploids are not only ideal materials to study species evolution, but also important bridges in incorporating genetic diversity of wild species into crops. Primary allopolyploids typically exhibit chromosome instability that a disadvantage trait in crop breeding. Newly synthesized hexaploid wheat has been widely used in wheat genetics and breeding studies. To better understand the cytological and genetic basis of chromosome instability, this study investigated the chromosomes of a large number of seeds derived from the synthetic wheat SHW-L1 and its hybrids with natural wheat. SHW-L1 exhibited persistent chromosome instability since we observed a high frequent chromosome variation de novo generated from euploid SHW-L1 plants at the 14th generation of selfing (F14). High frequent chromosome variations were also observed in the F2 hybrids and most of the analyzed recombinant inbred lines (RILs) at F14, derived from the cross of SHW-L1 with common wheat variety Chuanmai 32. Chromosome instability was associated with frequent univalency during meiotic metaphase I. The experiment on reciprocal crosses between SHW-L1 and Chuanmai 32 indicated that cytoplasm has not obvious effects on chromosome instability. An analysis on 48 F14 RILs revealed chromosome variation frequency was not associated with the Ph1 alleles from either SHW-L1 or Chuanmai 32, rejecting the hypothesis that chromosome instability was due to the Ph1 role of synthetic wheat. In the analyzed RILs, chromosome instability influences the phenotype uniformity, showing as obvious trait differences among plants within a RIL. However, the analyzed commercial varieties only containing ∼12.5% genomic components of synthetic wheat were chromosomally stable, indicating that chromosome instability caused by synthetic wheat can be effectively overcome by increasing the genetic background of common wheat.

Global transcriptome analysis of allopolyploidization reveals large-scale repression of the D-subgenome in synthetic hexaploid wheat

“…The expression level differences from polyploidization to achieve dosage-balance, to establish homoeollele-specific expression or in exhibiting genomic background effects, are all potentially the manifestation of the genetic and epigenetic changes that occur upon polyploidization. The chromosome-level analysis of synthetic lines and their tetraploid and diploid parents using molecular cytogenetic techniques have depicted structural differences in chromatin regions 70 , and genome sequence level analysis have also revealed similar outcomes 71 , 72 . In an epigenetic perspective, microRNAs (miRNAs), the key players in post transcriptional gene regulation, were expressed in a non-additive manner in resynthesized wheat 41 .…”

Chromosome stability of synthetic Triticum turgidum–Aegilops umbellulata hybrids

“…The newly synthetic wheat containing the active Ph1 gene was also associated with meiotic abnormality and aneuploidy in a parent-dependent manner [ 38 ]. The chromosome numbers in synthetic wheat range from 39 to 45, and the frequency of euploids (2 n = 42) is 51.4% [ 39 ]. The chromosome numbers (35–43) and the frequency of euploids (49.61%) in the current nascent synthetic T. turgidum – Ae.…”

“…The chromosome numbers (35–43) and the frequency of euploids (49.61%) in the current nascent synthetic T. turgidum – Ae. umbellulata species are close to those of synthetic hexaploid wheat [ 39 ]. The frequency of aneuploids in synthetic wheat SHW - L1 was 48.6%, though it decreased to 12.5% in a recombinant inbred line containing SHW - L1 blood [ 39 ] and was reduced to 1.3% and 3.0%, respectively, in the new wheat varieties ‘Shumai 969’ and ‘Shumai 830’ derived from SHW - L1 [ 40 ].…”

Karyotype Reorganization in Wheat–Rye Hybrids Obtained via Unreduced Gametes: Is There a Limit to the Chromosome Number in Triticale?

“…An attempt to resynthesize the ancient polyploid Arabidopsis suecica by crossing A. thaliana and A. arenosa produced a viable hybrid, which showed homologous pairing and no important structural reorganization of the homeologous genomes in F 5 [99]. In contrast, chromosomal variation is ubiquitous in newly developed synthetic hexaploid wheat (SHW) created by crossing T. turgidum with A. tauschii [100][101][102]. The common occurrence of univalency during meiotic metaphase I was associated with chromosome instability [102].…”

“…In contrast, chromosomal variation is ubiquitous in newly developed synthetic hexaploid wheat (SHW) created by crossing T. turgidum with A. tauschii [100][101][102]. The common occurrence of univalency during meiotic metaphase I was associated with chromosome instability [102]. Young allopolyploids, termed neopolyploids, are appropriate evolutionary model systems for understanding early allopolyploid formation.…”