A mutation in negative regulator of basal resistance WRKY17 of Arabidopsis increases susceptibility to Agrobacterium-mediated genetic transformation

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 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.