RESEARCH ARTICLE Conserved loci of leaf and in

Full list of author information is available at the end of the articlePlants and pathogens are in a constant struggle as each co-evolves to adapt to genomic changes. Plant genomes are adapting to different modes of infection by pathogens while pathogens are evolving different avenues to circum-vent defense systems of their respective hosts. Rust fungi are among the most economically important pathogens, yet are part of elusive host-pathogen systems. The order contains over 7,000 different species from 100 genera [1]. Adding to the complexity, individual cereal crops can be infected by several rust fungi adapted to the specific crop. Cereal rust fungi are obligate biotrophs and have alternate hosts where sexual recombination takes place, allowing for diversification of the population [2]. The life cycle of cereal rust fungi begins with a urediniospore landing on a leaf surface and germinating in the presence of adequate humidity. A germtube emerges and moves towards a stomate via a thigmotrophic response and * Correspondence: john.fellers@ars.usda.gov1USDA-ARS, Hard Winter Wheat Genetics Research Unit, Department of PlantAbstract Background: Wheat leaf rust (Puccinia triticina Eriks; Pt) and stem rust fungi (P. graminis f.sp. tritici; Pgt) are significant economic pathogens having similar host ranges and life cycles, but different alternate hosts. The Pt genome, currently estimated at 135 Mb, is significantly larger than Pgt, at 88 Mb, but the reason for the expansion is unknown. Three genomic loci of Pt conserved proteins were characterized to gain insight into gene content, genome complexity and expansion. Results: A bacterial artificial chromosome (BAC) library was made from P. triticina race 1, BBBD and probed with Pt homologs of genes encoding two predicted Pgt secreted effectors and a DNA marker mapping to a region o