|Samac, Deborah - Debby|
Submitted to: International Conference on Legume Genomics and Genetics
Publication Type: Abstract Only
Publication Acceptance Date: 3/10/2004
Publication Date: 6/7/2004
Citation: Foster-Hartnett, D., Penuela, S., Danesh, D., Sharapova, N., VandenBosch, K.A., Young, N.D., Samac, D.A. 2004. Histochemical and transcriptome analysis of the interactions between Medicago truncatula and the pathogens Colletotrichum trifolii and Erisyphe pisi [abstract]. Second International Conference on Legume Genomics and Genetics, June 7-11, 2004, Dijon, France. p. 239.
Technical Abstract: Anthracnose is a serious fungal disease of alfalfa (Medicago sativa) which is controlled by race-specific dominant resistance genes. In the field, infection of stems and crowns of susceptible adult plants with the causal agent Colletotrichum trifolii causes death of stems and crown rot that can lead to plant death. Susceptible seedlings infected in a controlled environment are rapidly colonized and killed. A collection of Medicago truncatula accessions was screened for seedling reaction to C. trifolii. The infection phenotype of selected accessions of M. truncatula has been compared with susceptible and resistant alfalfa seedlings by histochemical staining. We have identified three basic phenotypes: (1) resistance, characterized by cell collapse, production of phenolic compounds, and arrest of fungal growth; (2) moderate susceptibility, characterized by modest hyphal growth; and (3) non-host resistance, in which the rate of spore germination is reduced compared with the inoculated resistant reference, Jemalong (A17). Transcriptome analysis of the M. truncatula A17 cotyledon-C. trifolii early interaction (24 hours post-inoculation) was carried out with 6,000 EST microarray slides. Eighty-four ESTs were upregulated and two were downregulated by a minimum of two-fold relative to the uninoculated control. Preliminary results show up-regulation of genes previously identified to be involved in plant defense, hypersensitive reaction, and stress responses. The function of these genes may include flavonoid, stilbene, lignin, and phytoalexin production and cell-death regulation in resistant interactions, consistent with the phenotypes observed. Several genes of unknown function were also differentially regulated. Similar transcriptome analysis was performed with the A17-Erisyphe pisi (powdery mildew resistant) interaction on trifoliate leaves. Of the 84 ESTs upregulated in response to C. trifolii, 63 were also upregulated in response to powdery mildew infection, indicating that the response pathways to hemi-biotrophic/necrotrophic C. trifolii and a biotrophic E. pisi pathogen overlap significantly.