|Samac, Deborah - Debby|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 4/5/2005
Publication Date: 4/5/2005
Citation: Samac, D.A., Foster-Hartnett, D., Penuela, S., Sharopova, N., VandenBosch, K.A. 2005. Transcript profiling to identify genes associated with disease resistance in Medicago truncatula [abstract]. 2nd Australian Model Legume Workshop, April 5-8, 2005, Rottnest Island, Australia. Abstract No. 20.
Technical Abstract: Infection of plants by pathogens causes a large and rapid change in gene expression. We are using Medicago truncatula to identify and characterize the function of genes expressed during resistant interactions with pathogens. The genomic tools available make M. truncatula an excellent system to identify genes involved in biotic and abiotic stress resistance in legumes. A collection of accessions of M. truncatula was screened for reaction to Colletotrichum trifolii, the causal agent of anthracnose of alfalfa, and the powdery mildew pathogen, Erysiphe pisi. Histochemical analysis showed that epidermal cells of cotyledons of the resistant genotype Jemalong A17 respond to infection by C. trifolii with a hypersensitive response producing hydrogen peroxide, callose, and fluorescent phenolic compounds prior to necrosis and cell death. Three types of responses were identified in accessions responding to E. pisi; a resistant hypersensitive response, moderate resistance in which only limited fungal growth and sporulation occurred, and a susceptible interaction. Glass slide microarrays with 6,384 M. truncatula expressed sequence tags (ESTs) were used to examine gene expression in M. truncatula responding to C. trifolii 24 hours after inoculation (hai) or E. pisi 12 hai. The profile of up-regulated genes in response to C. trifolii was consistent with the cellular responses observed and included genes involved in flavonoid biosynthesis, peroxidase, pathogenesis-related proteins and cell-wall modifying enzymes. In the interaction with E. pisi, genes putatively involved in general responses to the pathogen were the well-known pathogenesis-related proteins thaumatin, peroxidase, chitinase, and PR10 as well as EDS1, which is involved in defense response signaling. A total of 22 genes was up- or down-regulated at least 2-fold specifically in the resistant interactions. Among the up-regulated genes were those encoding enzymes involved in flavonoid and lignin biosynthesis, a patatin-like phospholipase, xyloglucan endoglucanase inhibitor, putative ubiquitin ligase, putative acid phosphatase, MYB-like transcription factor, calcium-regulated receptor kinase, and uncharacterized proteins involved in plant-microbe interactions, at least one of which may be unique to legumes. Motif searches for conserved cis-elements in the promoters of 23 differentially regulated genes identified putative elements for binding of MYB-like, bZIP, ethylene, and jasmonic acid responsive transcription factors in the up-regulated genes. Results of transcript profiling experiments are consistent with a role for flavonoid compounds in resistance. These experiments also identified genes of unknown function that were differentially regulated, highlighting this approach as a tool for gene discovery.