Comparative analysis of Aegilops speltoides and wheat repetitive elements and development of S genome-specific FISH painting.

Abstract

Aegilops speltoides (2n = 2x = 14, genome SS) is a wild relative of wheat and a donor of useful traits for wheat improvement. Several whole-genome studies compared genic regions of Aegilops from the Sitopsis section and wheat and found that Ae. speltoides is most closely related to the wheat B subgenome but is not its direct progenitor. The results showed that a B subgenome ancestor diverged from Ae. speltoides more than 4 MYA and either has not yet been discovered, or is extinct. To further explore the evolutionary relationship between wheat and Ae. speltoides and develop Ae. speltoides chromosome paints, we performed comparative analysis of repetitive fractions of the S genome and three subgenomes of hexaploid wheat. The low-coverage sequence data were analyzed with RepeatExplorer pipeline to annotate repeats and estimate their content. The LTR-retrotransposons comprised about 80% of repeats in Ae. speltoides and wheat datasets and about two-third of them were LTR/Ty3-Gypsy. Ae. speltoides had 1.5 times more LTR/Ty-Copia repeats and 1.5 times less DNA transposons than wheat subgenomes. Several S genome-specific dispersed repeats were found and annotated. Their sequences were used to develop S genome-specific paints for detecting Ae. speltoides chromatin in the wheat background using fluorescent in situ hybridization.