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United States Department of Agriculture

Agricultural Research Service

Research Project: IMPROVING ALFALFA AND OTHER FORAGE CROPS FOR BIOENERGY, LIVESTOCK PRODUCTION, AND ENVIRONMENTAL PROTECTION

Location: Plant Science Research

Title: Identification of Novel Defense Response Genes in Medicago truncatula for Improving Disease Resistance in Alfalfa

Authors
item Samac, Deborah
item Penuela, Silvia -
item Schnurr, Judy
item Hunt, E. Nicole -
item Foster-Hartnett, Dawn -
item Vandenbosch, Kathryn -
item Gantt, Steve -

Submitted to: International Conference on Legume Genomics and Genetics
Publication Type: Abstract Only
Publication Acceptance Date: July 2, 2010
Publication Date: July 2, 2010
Citation: Samac, D.A., Penuela, S., Schnurr, J.A., Hunt, E., Foster-Hartnett, D., Vandenbosch, K.A., Gantt, S. 2010. Identification of Novel Defense Response Genes in Medicago truncatula for Improving Disease Resistance in Alfalfa [abstract]. Vth International Conference on Legume Genomics and Genetics, July 2-8, 2010, Pacific Grove, California. p. 45.

Technical Abstract: Infection of plants by pathogens initiates a cascade of defense responses that halt or limit pathogen growth. However, the role of many of the genes induced by pathogens is unknown. Transcript profiling was used to identify genes associated with defense responses in the model legume Medicago truncatula. We compared transcript profiles from leaves inoculated with a biotrophic pathogen (Erysiphe pisi, powdery mildew), hemibiotroph (Colletotrichum trifolii, anthracnose), and roots infected with a necrotroph (Phytophthora medicaginis, Phytophthora root rot) to identify genes expressed in response to all three pathogens and genes unique to an interaction. Among the most strongly up-regulated genes in all three interactions were a hevein-like protein, thaumatin-like protein (TLP), and members of the pathogenesis response (PR) 10 family. Transcripts of genes for enzymes in the phenylpropanoid pathway leading to production of isoflavonoid phytoalexins increased dramatically in response to inoculation with the foliar pathogens. Strongly up-regulated genes specific to a hypersensitive defense response included a putative 2-hydroxyisoflavanone dehydratase (PrMC3; BG587794), a protein of unknown function with weak similarity to amino acid transporters (Q9SGD7; BF518474), and a protein annotated as nod12a (CF068194), previously associated with root nodules. Expression of TLP, nod12a, PR10 family members, and chalcone synthase (CHS) family members were measured by qRT-PCR in healthy and infected leaves and roots of different M. truncatula accessions. Differential patterns were observed depending on susceptibility to the three pathogens. Transgenic M. truncatula plants expressing RNAi for PR10 and TLP were identified and tested for alteration in disease resistance. No increase in susceptibility was observed, although expression of TLP and PR10 were reduced to 0.1% and 2% of controls, respectively. However, plants expressing RNAi constructs for CHS were significantly more susceptible to C. trifolii and P. medicaginis than control plants. Transgenic alfalfa plants were produced expressing RNAi constructs for nod12a, PrMC3, and Q9SGD7. Expression of RNAi constructs for the latter two genes dramatically increased susceptibility of plants to C. trifolii. These results support the important role of phenylpropanoid pathway-derived compounds in disease resistance in legumes and the utility of a forward genetic approach for identifying genes important in plant defense.

Last Modified: 7/30/2014
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