Analysis of plant gene expression responses to the pathogen and natural genetic engineer Agrobacterium tumefaciens
Agrobacterium tumefaciens genetically transforms its natural plant host and other eukaryotic cells, representing both an intriguing pathogen and a vehicle for genetic engineering. Host responses to this bacterium have not been studied extensively in the past, although this understanding is critical for both practical applications in biotechnology and insights into host-microbe interaction. Here we present a study of plant gene expression responses to Agrobacterium infection. Two different plant species and two different large-scale approaches have been used to identify genes with altered expression during infection. By cDNA-AFLP we identified several transcripts from Ageratum conyzoides cell cultures that were regulated at 24 and 48 hours after infection with Agrobacterium . A number of these transcripts code for plant defense-related proteins which are also regulated by a non-pathogenic bacterium. However, a nodulin-like gene was regulated uniquely by Agrobacterium, suggesting that the closely-related symbiotic Rhizobium and Agrobacterium can provoke similar responses in plants. We observed that an attachment-deficient Agrobacterium mutant hyper-induces a set of plant defense genes and we propose that Agrobacterium can dampen plant defense responses by an attachment-dependent mechanism. The plant defense system is likely important in regulating infection since Ageratum cells with heightened defenses hinder transformation. By using microarrays, we also investigated the transcriptome of Arabidopsis thaliana cell cultures during a time-course of infection by Agrobacterium. Statistically significant alterations in gene expression are observed at 48 hours after infection, but not at earlier time points. The identity of the differentially expressed genes suggests similarities with classes of genes characterized in our previous studies and with other defense-related genes. Future microarray studies comparing infection with other pathogens, symbionts and various Agrobacterium mutants will further advance our understanding of this fascinating plant-bacterium interaction.
- Biology