Expression of coordinately regulated defence response genes and analysis of their role in disease resistance in Medicago truncatula

Abstract

Microarray technology was used to identify the genes associated with disease defence responses in the model legume Medicago truncatula. Transcript profiles from M. truncatula cv. Jemalong genotype A17 leaves inoculated with Colletotrichum trifolii and Erysiphe pisi and roots infected with Phytophthora medicaginis were compared to identify the genes expressed in response to all three pathogens and genes unique to an interaction. The A17 genotype is resistant to C. trifolii and E. pisi, exhibiting a hypersensitive response after inoculation, and is moderately susceptible to P. medicaginis. Among the most strongly up-regulated genes in all three interactions were those encoding 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 the production of isoflavonoid phytoalexins increased dramatically in response to inoculation with the foliar pathogens. In P. medicaginis-inoculated roots, transcripts of genes in the phenylpropanoid pathway peaked at 5 days post-inoculation, when symptoms became visible. Transcript accumulation of three PR10 family members, a TLP and chalcone synthase (CHS) was assessed in M. truncatula genotype R108 plants. The R108 plants are resistant to C. trifolii and moderately susceptible to E. pisi and P. medicaginis. Transcript accumulation paralleled the stages of pathogen development. To evaluate the role of a TLP, a PR10 family member and CHS in disease resistance, transgenic R108 plants containing interfering RNA (RNAi) constructs were produced. Reduced expression of PR10 and TLP had no effect on the disease phenotype, whereas reduced expression of CHS resulted in increased susceptibility to necrotrophic pathogens.

Spatio-Temporal Expression Patterns of Arabidopsis thaliana and Medicago truncatula Defensin-Like Genes

“…The accession A17 is moderately susceptible to P. medicaginis with lesions being typically small and occurring about 5 dpi [51]. Our preliminary study using qRT-PCR detected the highest significant differential expression of two antimicrobial genes ( thaumatin-like protein and PR10 ) occurred at 4 dpi with P. medicaginis .…”

“…For Phytophthora -infected roots, germinated seeds were placed in CYG seed germination pouches (Mega International, West St. Paul, MN), grown, and inoculated as described previously [51]. At 4 dpi, infected hypocotyl and root segments were harvested from both the infected and mock-inoculated plants, frozen immediately in liquid nitrogen, and held at −80°C for subsequent RNA extraction.…”

Achievements and Challenges in Legume Breeding for Pest and Disease Resistance

“…Gene expression studies provide information about the genes and metabolic pathways differentially regulated during plant-pathogen interactions and contribute to the identification of candidate resistance genes involved in each of these steps of the defense response (Foster-Hartnett et al, 2007;Uppalapati et al, 2009;Fondevilla et al, 2011c;Samac et al, 2011;Rispail et al, 2013;Barilli et al, 2014). Knowledge of the genes involved in defense can be useful for marker assisted selection (MAS) and also to select genes whose altered expression through transformation can result in an increased resistance.…”

Medicago truncatula DNF2 is a PI‐PLC‐XD‐containing protein required for bacteroid persistence and prevention of nodule early senescence and defense‐like reactions

“…Similar expression patterns were obtained for the dnf2-2 and dnf2-3 alleles (data not shown). Table S1), which is a molecular marker of plant defense (Samac et al, 2011). Elevated levels of PR10 transcript were found in dnf2-4 mutant nodules at 10 dpi.…”