|Samac, Deborah - Debby|
Submitted to: North American Alfalfa Improvement Conference
Publication Type: Abstract Only
Publication Acceptance Date: 7/21/2004
Publication Date: 7/21/2004
Citation: Samac, D.A., Foster-Hartnett, D., Penuela, S., Danesh, D., Vandenbosch, K. 2004. Transcript profiling in Medicago truncatula responding to infection by Erysiphe pisi and Colletotrichum trifolii [abstract]. 19th North American Alfalfa Improvement Conference, July 19-21, 2004, Ste Foy, Quebec, Canada. Available: http://www.naaic.org/Meetings/National/2004NAAIC&TC/2004abstracts/dsamac-2.pdf.
Technical Abstract: Medicago truncatula is a model for legume genomics, exhibiting simple genetics and a genome highly conserved with alfalfa and pea. The large collection of molecular tools make M. truncatula an excellent system to identify genes involved in biotic and abiotic stress tolerance in legumes. We are using M. truncatula to isolate disease resistance genes and to identify and characterize the function of genes expressed during resistant interactions with pathogens. A collection of 119 accessions of M. truncatula, including 10 cultivars, was screened for reaction to Colletotrichum trifolii, the causal agent of anthracnose of alfalfa. A majority of the entries showed moderate to complete cotyledon yellowing, classified as a resistant response. Approximately 18% of the entries showed little to no response, classified as a potential non-host reaction. Histochemical staining showed that the reduction or absence of symptoms on at least one accession was correlated with reduction in spore germination compared with germination on the resistant genotype. In the resistant interaction, production of hydrogen peroxide, epidermal cell browning, and callose production was observed 48 hours post inoculation. An alfalfa isolate of powdery mildew identified as Erysiphe pisi was used to inoculate resistant and susceptible accessions of M. truncatula in the greenhouse. At 48 hours post inoculation the resistant accession exhibited auto-fluorescence at the site of fungal penetration, indicating the presence of phenolic compounds, and the germinating spore had collapsed. Glass slide microarrays with 6,384 M. truncatula ESTs were used to examine gene expression in M. truncatula responding to E. pisi or C. trifolii. In response to C. trifolii, 84 genes were up-regulated at least 2-fold and 2 genes were down-regulated, compared with mock-inoculated plants. In the resistant response to E. pisi, 361 genes were up-regulated and 192 genes were up-regulated in leaves of the susceptible accession. A total of 50 genes were up-regulated by both E. pisi and C. trifolii in resistant interactions indicating that the response pathways to both pathogens overlap significantly. A majority of the characterized genes are involved in flavonoid, stilbene, lignin, and phytoalexin production and cell-death regulation, consistent with the phenotypes observed. Several genes of unknown function were also differentially regulated, highlighting this approach as a tool for gene discovery.