WRKY72‐type transcription factors contribute to basal immunity in tomato and Arabidopsis as well as gene‐for‐gene resistance mediated by the tomato R gene Mi‐1

Abstract

SUMMARYWRKY transcription factors play a central role in transcriptional reprogramming associated with plant immune responses. However, due to functional redundancy, typically the contribution of individual members of this family to immunity is only subtle. Using microarray analysis, we found that the paralogous tomato WRKY genes SlWRKY72a and b are transcriptionally up-regulated during disease resistance mediated by the R gene Mi-1. Virus-induced gene silencing of these two genes in tomato resulted in a clear reduction of Mi-1-mediated resistance as well as basal defense against root-knot nematodes (RKN) and potato aphids. Using Arabidopsis T-DNA insertion mutants, we found that their Arabidopsis ortholog, AtWRKY72, is also required for full basal defense against RKN as well as to the oomycete Hyaloperonospora arabidopsidis. Despite their similar roles in basal defense against RKN in both tested plant species, WRKY72-type transcription factors in tomato, but not in Arabidopsis, clearly contributed to basal defense against the bacterial pathogen Pseudomonas syringae. Of the five R genes that we tested in tomato and Arabidopsis, only Mi-1 appeared to be dependent on WRKY72-type transcription factors. Interestingly, AtWRKY72 target genes, identified by microarray analysis of H. arabidopsidis-triggered transcriptional changes, appear to be largely non-responsive to analogs of the defense hormone salicylic acid (SA). Thus, similarly to Mi-1, which in part acts independently of SA, AtWRKY72 appears to utilize SA-independent defense mechanisms. We propose that WRKY72-type transcription factors play a partially conserved role in basal defense in tomato and Arabidopsis, a function that has been recruited to serve Mi-1-dependent immunity.

GroEL from the endosymbiont Buchnera aphidicola betrays the aphid by triggering plant defense

“…Tomato cultivar Moneymaker plants were maintained as described previously (43). Arabidopsis bak1-5 mutant, in a Col-0 genetic background (44), and wild-type Arabidopsis Col-0 plants were grown under a 12 h light photoperiod.…”

“…UC82B and mustard India plants, respectively, and maintained as described in refs. 43,45. Age-synchronized 1-d-old adult aphids were produced as described in ref.…”

The Impact of Plant-Parasitic Nematodes on Agriculture and Methods of Control

“…Their ability to bind to pathogen responsive cis acting W-box promoter elements in PR1 genes is indicative of their role in plant immunity [113]. Arabidopsis WRKY72 was reported to have a signiicant contribution to Mi-1-mediated defense against RKNs, potato aphids [114] and oomycete pathogen Hyaloperonospora arabidopsidis the causal agent of downy mildew [115]. WRKY gene expression is altered during plantparasitic nematode interactions.…”

The rice <i>GRH2</i> and <i>GRH4</i> activate various defense responses to the green rice leafhopper and confer strong insect resistance

“…and potato aphids (Macrosiphum euphorbiae) (Bhattarai et al 2007). Virus-induced gene silencing of the transcription factors SlWRKY72a and SlWRKY72b in tomato resulted in a reduction of Mi-1-mediated resistance as well as basal defense against RKN and potato aphids (Bhattarai et al 2010). The tomato receptor-like kinase SlSERK1 is required for Mi-1-mediated resistance to potato aphids (Mantelin et al 2011).…”