Differential Roles of Glucosinolates and Camalexin at Different Stages of Agrobacterium-Mediated Transformation

Summary Agrobacterium tumefaciens is the causal agent of crown gall disease in a wide range of plants via a unique interkingdom DNA transfer from bacterial cells into the plant genome. A. tumefaciens is capable of transferring its T-DNA into different plant parts at different developmental stages for transient and stable transformation. However, the plant genes and mechanisms involved in these transformation processes are not well understood. We used Arabidopsis thaliana Col-0 seedlings to reveal the gene expression profiles at early time points during Agrobacterium infection. Common and differentially expressed genes were found in shoots and roots. A gene ontology analysis showed that the glucosinolate (GS) biosynthesis pathway was an enriched common response. Strikingly, several genes involved in indole glucosinolate (iGS) modification and camalexin biosynthesis pathway were up-regulated while genes in aliphatic GS (aGS) biosynthesis were generally down-regulated upon Agrobacterium infection. Thus, we evaluated the impacts of GSs and camalexin during different stages of Agrobacterium-mediated transformation combining Arabidopsis mutant studies, metabolite profiling, and exogenous applications of various GS hydrolysis products or camalexin. The results suggest that the iGS hydrolysis pathway plays an inhibitory role in transformation efficiency on Arabidopsis seedlings at the early infection stage. Later in the Agrobacterium infection process, accumulation of camalexin was a key factor inhibiting tumor development on Arabidopsis inflorescence stalks. In conclusion, this study revealed the differential roles of glucosinolates and camalexin at different stages of Agrobacterium-mediated transformation and provided new insights into crown gall disease control and improvement of plant transformation. This article is protected by copyright. All rights reserved.