The B-3 ethylene response factor MtERF1-1 mediates resistance to a subset of root pathogens in Medicago truncatula without adversely affecting symbiosis with rhizobia

Differential expression of peach ERF transcriptional activators in response to signaling molecules and inoculation with Xanthomonas campestris pv. pruni

Ethylene response factors (ERFs) are a large family of transcription factors (TFs) that have diverse functions in plant development and immunity. However, very little is known about the molecular regulation of these TFs in stone fruits during disease incidence. In the present study, we describe the identification of five peach ERFs (Pp-ERFs), aiming to elucidate their potential roles in defense against Xanthomonas campestris pv. pruni (Xcp), the causal agent of bacterial spot disease. The phylogenetic analysis along with sequence comparisons indicated that all Pp-ERFs are transcriptional activators belonging to groups IX and IIV ERFs. The transactivation capacity of these proteins was verified in vivo where they all induced the expression of the GUS reporter gene and in a GCC-dependent manner. The nuclear localization was also confirmed for two of these proteins, Pp-ERF2.b and Pp-ERF2.c, after their transient expression in onion epidermal cells. The induction kinetics of Pp-ERFs after inoculation with Xcp was determined by qRT-PCR. Except for Pp-ERF2.b, transcript levels of Pp-ERFs increased strongly and rapidly in the resistant 'Venture' compared to the susceptible 'BabyGold 5' cultivar after infection with Xcp. In contrast, the expression of Pp-ERF2.b was several-fold higher in the susceptible cultivar after bacterial infection. The expression of Pp-ERFs was also monitored after treating with signaling compounds; salicylic acid (SA) (1 mM), ethephon (1 mM) and methyl jasmonate (MeJA) (50 μM). Although the results generally emphasize the role of ethylene/jasmonic acid (ET/JA) signaling pathways in regulating the expression of Pp-ERFs, there was a coordination of the timing of ET/JA responses, suggesting compensatory rather than synergistic interactions between these pathways during defense against Xcp.

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

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.