Genetics. Published Articles Ahead of Print: June 18, 2008, Copyright © 2008
doi:10.1534/genetics.108.089599


A more recent version of this article appeared on July 1, 2008.

REGULAR RESEARCH PAPERS

The Origin of a "Zebra" Chromosome in Wheat Suggests Nonhomologous Recombination as a Novel Mechanism for New Chromosome Evolution and Step Changes in Chromosome Number

Peng Zhang 1, Wanlong Li 2, Bernd Friebe 2* and Bikram S Gill 2

1 University of Sydney
2 Wheat Genetic Genomic Recources Center

* To whom correspondence should be addressed. E-mail: friebe{at}ksu.edu.

Submitted on March 27, 2008
Revised on April 11, 2008
Accepted on 15 April 2008


Abstract

An alloplasmic wheat line, TA5536, with a "zebra" chromosome z5A was isolated from an Elymus trachycaulus/Triticum aestivum backcross derivative. This chromosome was named "zebra" because of its striped genomic in situ hybridization pattern. Its origin was traced to nonhomologous chromosomes 5A of wheat and 1Ht of Elymus; four chromatin segments were derived from chromosome 1Ht and five including the centromere from 5A. In this study, our objective was to determine the mechanism of origin of chromosome z5A, whether by nonhomologous recombination or by multiple translocation events. Different crossing schemes were used in order to recover recombinants containing various Elymus chromatin segments of the z5A chromosome. In addition, one z5AL telocentric chromosome and three z5AL isochromosomes were recovered. The dissection of the Elymus segments into different stocks allowed us to determine the marker order and suggested that the "zebra" chromosome originated from nonhomologous recombination. We present a model of possible mechanism(s) of chromosome evolution and step changes in chromosome number applicable to a wide range of organisms.

Key Words: GISH, chromosome evolution, nonhomologous recombination, translocation, wheat