|Samac, Deborah - Debby|
Submitted to: American Association for the Advancement of Science Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 12/5/2002
Publication Date: N/A
Technical Abstract: The forage legume Medicago truncatula is an excellent model for investigating functional genomics of plant-microbe interactions. Partial sequencing of cDNA clones from 17 libraries has contributed to the 164,441 expressed sequence tags (ESTs) from M. truncatula that have been deposited in GenBank. The ESTs define 33,765 unique sequences in the M. truncatula Gene Index (www.tigr.org/tdb/tgi/mtgi/). Glass slide microarrays containing 1,152 ESTs printed in triplicate were used for hybridization with labeled targets derived from pathogen-infected and non-inoculated leaf and root tissues. Comparisons of gene expression profiles of M. truncatula interactions with two foliar fungal pathogens (Colletotrichum trifolii and Erysiphe pisi) and one root oomycete pathogen (Phytophthora medicaginis) were performed. In the C. trifolii interaction, 54 genes were differentially expressed, 19 genes were differentially expressed by infection with E. pisi, and 35 genes were differentially expressed by P. medicaginis infection. Hierarchical clustering of pathogen-challenged tissues showed that expression profiles of plants challenged with P. medicaginis and C. trifolii were more closely related to each other than to the profile observed with E. pisi. This may reflect the strong hypersensitive reaction (disease resistance) observed in the interaction of E. pisi with M. truncatula "Jemalong A17" and that E. pisi is an obligate parasite. Two-dimensional clustering analysis showed that out of 48 clones representing disease defense-response genes, 19 were up-regulated across all experiments. Only 5 clones showed down-regulation in all experiments. Out of 127 genes with unknown function, 14 were down-regulated in all experiments and only 1 clone was up-regulated in all cases. Several subgroups of ESTs with unknown function were associated with defense-response genes using self-organizing maps partitioning suggesting a role in disease response. A time course experiment of M. truncatula roots challenged with P. medicaginis showed a number of differentially expressed genes at each time point. At 2 days after inoculation, with the development of the first symptoms, 52 genes were up-regulated, including most of the defense-response genes, and 26 genes were down-regulated, including many genes involved in symbiotic root nodule formation. These studies will provide insight into disease resistance mechanisms and accelerate the pace of discovery of agriculturally important genes.