Reassessment of the evolution of wheat chromosomes 4A, 5A, and 7B

Jan Dvorak,Karin R Deal,Patrick E Mcguire,Le Wang,Ming-Cheng Luo,Chad M Jorgensen,Tingting Zhu,Katrien M Devos,Bikram S Gill,Yong Q Gu,Peng Qi,Assaf Distelfeld

doi:10.1007/s00122-018-3165-8

Abstract

Key messageComparison of genome sequences of wild emmer wheat and Aegilops tauschii suggests a novel scenario of the evolution of rearranged wheat chromosomes 4A, 5A, and 7B.Past research suggested that wheat chromosome 4A was subjected to a reciprocal translocation T(4AL;5AL)1 that occurred in the diploid progenitor of the wheat A subgenome and to three major rearrangements that occurred in polyploid wheat: pericentric inversion Inv(4AS;4AL)1, paracentric inversion Inv(4AL;4AL)1, and reciprocal translocation T(4AL;7BS)1. Gene collinearity along the pseudomolecules of tetraploid wild emmer wheat (Triticum turgidum ssp. dicoccoides, subgenomes AABB) and diploid Aegilops tauschii (genomes DD) was employed to confirm these rearrangements and to analyze the breakpoints. The exchange of distal regions of chromosome arms 4AS and 4AL due to pericentric inversion Inv(4AS;4AL)1 was detected, and breakpoints were validated with an optical Bionano genome map. Both breakpoints contained satellite DNA. The breakpoints of reciprocal translocation T(4AL;7BS)1 were also found. However, the breakpoints that generated paracentric inversion Inv(4AL;4AL)1 appeared to be collocated with the 4AL breakpoints that had produced Inv(4AS;4AL)1 and T(4AL;7BS)1. Inv(4AS;4AL)1, Inv(4AL;4AL)1, and T(4AL;7BS)1 either originated sequentially, and Inv(4AL;4AL)1 was produced by recurrent chromosome breaks at the same breakpoints that generated Inv(4AS;4AL)1 and T(4AL;7BS)1, or Inv(4AS;4AL)1, Inv(4AL;4AL)1, and T(4AL;7BS)1 originated simultaneously. We prefer the latter hypothesis since it makes fewer assumptions about the sequence of events that produced these chromosome rearrangements.

Highlights

The genome of hexaploid bread wheat (Triticum aestivum, 2n = 6x = 42) consists of three subgenomes designated as A, B, and D
To summarize, starting at the tip of the present-day arm 4AS, the global dot-plots in Fig. 1a confirmed that the 4A pseudomolecule is homoeologous to the Ae. tauschii reference chromosome arms in the following sequence starting at the tip of the 4A short arm: 4DL-centromere-4DS-5DL-4DL-7DS
We identified a synteny block 1,084,387 bp long in the wild emmer wheat chromosome arm 4AS, which contained 9 high confidence (HC) genes that were collinear with Ae. tauschii genes located at the tip of arm 4DS

Summary

Introduction

The genome of hexaploid bread wheat (Triticum aestivum, 2n = 6x = 42) consists of three subgenomes designated as A, B, and D. The A subgenome was contributed by wild einkorn wheat T. urartu (Dvorak et al 1988, 1993), the B subgenome was contributed by an unknown species closely related to Aegilops speltoides (Dvorak and Zhang 1990), and the D subgenome was contributed by Ae. tauschii (Kihara 1944; McFadden and Sears 1946; Wang et al 2013). Extended author information available on the last page of the article most of the 21 bread wheat chromosomes could be assigned to a subgenome and one of the seven homoeologous chromosome groups (Sears 1966)

Methods

Results

Conclusion