Abstract
Agrobacterium is a phytopathogenic bacterium that induces crown gall disease in many plant species by transferring and integrating a segment of its own DNA (T-DNA) into its host genome. Whereas Agrobacterium usually does not trigger an extensive defense response in its host plants, it induces the expression of several defense-related genes and activates plant stress reactions. In the complex interplay between Agrobacterium and its host plant, Agrobacterium has evolved to take advantage of these plant defense pathways for its own purpose of advancement of the infection process. For example, Agrobacterium utilizes the host stress response transcriptional regulator VIP1 to facilitate nuclear import and proteasomal uncoating of its T-DNA during genetic transformation of the host cell. In Arabidopsis, the VIP1 gene expression is repressed by WRKY17, a negative regulator of basal resistance to Pseudomonas. Thus, we examined whether WRKY17 is also involved in plant susceptibility to genetic transformation by Agrobacterium. Using reverse genetics, we showed that a wrky17 mutant displays higher expression of the VIP1 gene in roots, but not in shoots. In a root infection assay, the wrky17 mutant plants were hyper-susceptible to Agrobacterium compared to wild type plants. WRKY17, therefore, may act as a positive regulator of Arabidopsis resistance to Agrobacterium. This notion is important for understanding the complex regulation of Agrobacterium-mediated transient genetic transformation; thus, although this paper reports a relatively small set of data that we do not plan to pursue further in our lab, we believe it might be useful for the broad community of plant pathologists and plant biotechnologists.
Highlights
WRKY protein family is composed of at least 74 members in Arabidopsis thaliana[1]; they act as transcriptional regulators and participate mainly in the control of gene expression involved in the plant stress response, and, in the induction of gene expression by pathogen-derived elicitors
We investigated the effect of the WRKY17 mutation on the expression of the VIP1 gene
The wrky[17] mutant is hypersusceptible to Agrobacteriummediated genetic transformation Once we had identified plant tissue showing a clear effect of WRKY17 on VIP1 expression, we investigated whether this effect altered susceptibility to Agrobacterium infection
Summary
WRKY protein family is composed of at least 74 members in Arabidopsis thaliana[1]; they act as transcriptional regulators and participate mainly in the control of gene expression involved in the plant stress response, and, in the induction of gene expression by pathogen-derived elicitors. Arabidopsis WRKY17, together with another family member WRKY11, is a negative regulator of the basal defense response[2]. The WRKY17 and WRKY11 genes are usually induced during the defense response, and Arabidopsis loss-of-function mutants wrky[17] and wrky[11] display higher expression of numerous stress- or defense-related genes and show increased resistance to infection by Pseudomonas, but not by other pathogens. The VIP1related defense responses are activated during Agrobacterium-host plant interactions, and Agrobacterium has evolved to subvert them to facilitate the infection process[4,6]
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