Interactions of Arabidopsis and M. truncatula with the same pathogens differ in dependence on ethylene and ethylene response factors

Abstract

Microbial pathogens inflict large losses to agriculture annually and thus mechanisms of plant resistance and how to deploy them to enhance disease resistance in crops are foci of much research interest. We recently described the important role of ethylene and Ethylene Response transcription Factors (ERFs), particularly MtERF1-1, in mediating resistance to the fungal pathogen Rhizoctonia solani in the model legume, Medicago truncatula. Previous studies on the closely related AtERF14, a master regulator of ethylene dependent defenses including other ERFs, suggested that in Arabidopsis these defenses were not essential for resistance to the same R. solani isolate but were required for resistance to another fungal pathogen, Fusarium oxysporum. Medicago plants with roots over-expressing MtERF1-1 were challenged with F. oxysporum but showed no altered resistance. These results further support a potential for divergent roles of ethylene associated defenses in different plant hosts responding to the same pathogen.

Figure 1

Response of M. truncatula with transgenic roots to inoculation with Fusarium oxysporum f.sp. medicaginis. (A) The number of healthy leaves per plant at 14 days post-inoculation (dpi). Medicago plants with transgenic roots overexpressing either MtERF1-1 (Ox-MtER F1-1) or GFP as a control (Ox-GFP) were produced according to Anderson et al. Plants on Fahräeus medium agar plates were inoculated with 1 × 10⁶ F. oxysporum f.sp. medicaginis spores in 1 ml of sterile water (Fom). 1 ml of sterile water was added to mock-treated plants (Mock). Plants were incubated at a constant temperature of 28ΰC α 2ΰC with a 16-h/8-h photoperiod at 200 mmol m⁻² s⁻¹. n ≥ 5. (B) In planta biomass of F. oxysporum as indicated by the amount of fungal DNA normalized to host plant DNA determined by quantitative PCR according to Anderson et al. Fungal biomass is presented relative to the amount in the Ox-GFP controls. Primers for F. oxysporum and M. truncatula are described in Anderson et al.,