Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: June 12, 2011
Publication Date: June 13, 2011
Citation: Szabo, L.J., Cuomo, C.A., Jin, Y., Rouse, M.N., Olivera, P. 2011. Puccinia graminis: variation is the rule. Meeting Abstract. p. 35. Technical Abstract: For nearly a century, characterization of Puccinia graminis f. sp. tritici (Pgt) populations has been based on phenotypic race pathotyping. These studies have shown a wide range of diversity worldwide. In regions where the alternate host is lacking, populations often have limited race diversity and are stable over long periods of time, with gradual step-wise changes. Occasionally, dramatic race shifts occur, often a result of an introduction of a new race. In contrast, when the alternate host is present, local population are extremely diverse and major race shifts occur frequently. Limited genetic studies and recent genotyping using molecular markers have indicated that the Pgt genome contains a high level of allelic variation between the two haploid genomes in this dikaryotic fungus. The recent sequencing of Pgt has shed new light on the complexity and diversity of the genome. The genome is much larger (88.6 Mb) than other sequenced fungal genomes resulting from a massive expansion of transposable elements, which comprise approximately 45% of the genome. A similar genome expansion (101 Mb) driven by transposable elements was also observed in the poplar leaf rust pathogen, Melampsora larici-populina (Mlp). Although these two rust fungi are phylogenetically diverse, it was surprising that very little synteny exists between the two genomes indicating that massive genome rearrangement has occurred and may play an important role in the evolution of rust fungi. Re-sequencing using Next Generation technology demonstrated a very high rate of single nucleotide polymorphisms (SNPs) between the two nuclei within a cell (130,000 SNPs) and between isolates (240,000-479,000 SNPs). The frequency of SNPs in the Pgt genome is approximately twice that found in the Mlp genome. Using the genome sequence data, molecular markers based on SNPs have been developed. SNP analysis of isolates of Ug99 and related races (Ug99 race group) has shown genetic diversity not only between isolates representing different races, but also isolates of the same race. In addition, SNP based markers have been used for the development of molecular diagnostic tools for rapid identification of the Ug99 race group. Genome analysis of Pgt and other rust fungi is providing new tools for analysis and insight into evolution of these important plant pathogens.