The transcriptome of Arabidopsis roots infected with Phytophthora parasitica identifies members of the VQ and DC1 families required for plant defense and susceptibility

Abstract

Little is known about the responses of plant roots to filamentous pathogens, particularly for oomycetes. We investigated the overall changes in gene expression in A. thaliana roots challenged with P. parasitica. We analyzed various infection stages, from penetration by the pathogen and establishment of the interaction to the switch from biotrophy to necrotrophy. We then carried out functional analyses, to identify the functions involved in plant defense. The A. thaliana transcriptome displays a dynamic response to P. parasitica infection, from penetration onwards. Some genes were specifically coregulated during penetration and biotrophic growth of the pathogen. Many of these genes had functions relating to primary metabolism, plant growth, and defense responses. In addition, many genes encoding DC1 domain- and VQ motif-containing proteins were found to be upregulated in plant roots, early in infection. Inactivation of two DC1 domain-containing proteins and VQ29 genes significantly increased susceptibility to P. parasitica infection. These proteins thus contribute to root defense responses, restricting penetration and the biotrophic growth of the oomycete pathogen. By contrast, inactivation of another DC1 domain-containing proteins significantly reduced susceptibility to P. parasitica infection. This protein thus favours P. parasitica development in roots. Our data suggest that the particular genetic program specifically activated during penetration may determine the outcome of pathogen invasion.