Homoeologous Relationships of Aegilops caudata and Wheat Chromosomes as Determined by Single Gene FISH Mapping

Aegilops caudata L. (=Ae. markgrafii (Greuter) Hammer, 2n = 14), a diploid wild relative of bread wheat is a source of agronomically important traits for wheat improvement. Ae. caudata is also an interesting example of speciation within the tribe Triticeae because of its highly rearranged genome; its structure and evolution have not been studied in detail. Fluorescence in situ hybridization (FISH) is a useful tool for studying chromosome organization. To overcome the problem of high content of repetitive elements in Triticeae genomes (80-90%), repeats free cDNAs can be used to develop chromosome specific FISH probes. Earlier we had developed a wheat physical map with several cDNA FISH markers located on each of the 14 homoeologous chromosome arms. All wheat cDNA FISH probes produced distinct signals on chromosomes of Ae. caudata, and allowed elucidation of their macrostructure and homoeology to wheat. Three submetacentric chromosomes, designated previously as A, C and D are homoeologous and mostly colinear to wheat group 1, 5 and 6 chromosomes respectively; though the long arm of chromosome D has a terminal translocation from chromosome E (group 7). Other chromosomes are highly rearranged: submetacentric B and acrocentric E, F and G contain regions homoeologous to wheat groups 2, 7, 3 and 4 respectively, involved mostly in intrachromosomal rearrangements but some interchromosomal translocations as well. Location of near-centromeric cDNA probes and wheat centromere specific transposable element showed that the centromeres of Ae. caudata chromosomes did not change their positions compared with their wheat homoeologs.