Submitted to: Plant Pathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/14/2011
Publication Date: 11/20/2011
Citation: Tremblay, A., Hosseini, P., Li, S., Alkharouf, N., Matthews, B.F. 2011. Identification of genes expressed by Phakopsora pachyrhizi, the pathogen causing soybean rust, at a late stage of infection of susceptible soybean leaves. Plant Pathology. 60:1-14. Interpretive Summary: Soybean is among the top five crops in the U.S. in terms of economic value. Numerous pathogens attack this crop. The soybean rust fungus is an important soybean pathogen which has been in the U.S. since 2004. We used DNA deep sequencing technology to study gene expression during the development process of this fungus on soybean so we can build a new resistance mechanism in soybean through biotechnology. We focused our research on a late stage of infection (10 days after infection) which corresponds to the production of the second generation of spores responsible of disease spreading. Many genes were expressed that are involved in a range of host metabolic processes. These results demonstrate that the pathogen at the latest stage of infection is expressing many genes important for spore production. This information provides candidate genes useful to develop a broader resistance to this pathogen by impairing soybean rust spore production and disease spread. Also, this information will be useful in the future for scientists to develop soybean rust resistant cultivars.
Technical Abstract: Soybean is one of the top five agricultural products in the United States and is highly susceptible to P. pachyrhizi, an exotic obligate biotrophic fungus. The amount of genomic information about P. pachyrhizi is small, which limits our understanding of the soybean-soybean rust pathogen interaction and the possibility of engineering resistance to this pathogen in soybean. Illumina mRNA-Seq analysis revealed P. pachyrhizi genes expressed during a biotrophic interaction between P. pachyrhizi and soybean during fungal sporulation at 10 days after inoculation. Approximately 2.4 million DNA sequences represented portions of potential P. pachyrhizi genes assembled into 32,940 contigs which were used to search against EST, protein and conserved domains databases. About 7,500 contigs represent newly discovered P. pachyrhizi sequences. Of these 7,500 contigs, 527 shared similarity to genes encoding fungal proteins involved in different metabolic pathways such as galactose and glycogen metabolism, glycolysis, citrate cycle, fatty acid metabolism, amino acid metabolism, proteolysis, protein synthesis, cell cycle division and mitosis, and cell wall biogenesis. Almost 7,000 potential P. pachyrhizi genes are still of unknown function. Such information may be useful in the development of new methods of broadening resistance of soybean to P. pachyrhizi, including the silencing of important P. pachyrhizi genes and also to understand the molecular basis of soybean-P. pachyrhizi interactions.