Submitted to: Plant Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/27/2010
Publication Date: 4/27/2010
Citation: Tremblay, A., Hosseini, P., Alkharouf, N., Li, S., Matthews, B.F. 2010. Transcriptome Analysis of a Compatible Response by Glycine max to Phakopsora pachyrhizi Infection. Plant Science. 179:183-193. Interpretive Summary: Soybean is among the top five crops in the U.S. in terms of economic value and numerous pathogens attack this crop. The soybean rust fungus originates from Asian and is an important soybean pathogen which has been in the U.S. since 2004. It can be responsible for 37 to 67% losses in soybean yield. We need to understand the development process of this fungus on soybean as well as which soybean genes are affected during the infection process 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) and on infection sites only. We identified numerous genes that functioned or were “expressed” at a higher level in a rust infected plant as compared to that of a healthy soybean plant. We also identified genes expressed at a lower level in the infected plants. Most of the genes expressed at a high level are involved in basic disease defense mechanisms, while genes expressed at low levels are involved in many different metabolic activities or pathways. These results demonstrate that the pathogen at the latest stage of infection strongly affects plant metabolism and that the plant futilely fights the pathogen even at the end of the infection process. This information provides candidate genes useful to develop a broader resistance to this pathogen which 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. Soybean rust is caused by the obligate fungus Phakopsora pachyrhizi Sydow, an exotic pathogen in the U.S. Extensive screening of soybean germplasm has not identified soybean with resistance to all of the different isolates of soybean rust. Gene expression analysis has been reported on plant infected at many stages of soybean-soybean rust interaction covering 6 hours after infection which corresponds to the first infection structure formation named appressorium through 7 days after infection (dai) where the first uredinium is developing. However, what is happening to the plant at the latest stage of infection (10 dai) where new spores are produced? A biotechnological approach may help to understand the plant host response at the molecular level and subsequently broaden resistance of soybean to this fungus. Using laser capture microdissection, we isolated susceptible soybean palisade cells showing signs of infection, extracted the RNA and performed transcriptome profiling using an Affymterix® soybean GeneChip®. A total of 938 genes were found to be differentially expressed, of which 164 were up-regulated, and 774 were down-regulated. Eighty-eight percent of our regulated genes are unique to our time-point and our palisade cells compare to the other gene expression experiments at earliest time-points. Gene expression data was overlaid on Kyoto Encyclopedia of Genes and Genomes (KEGG) biochemical pathways. In general, up-regulated genes were associated with basic defense while down-regulated genes were associated with many metabolic pathways such as photosynthesis, pentose phosphate and carbon fixation metabolism. These results demonstrate that soybean rust strongly affects plant metabolism at the latest stage of infection and that the plant futilely fights even at the end of the infection process to establish a resistance response. This information provides candidate genes useful to develop a broader resistance to soybean rust.