Differential roles of glucosinolates and camalexin at different stages of Agrobacterium-mediated transformation.

Po-Yuan Shih,Rosalia Deeken,Shu-Jen Chou,Erh-Min Lai,Barbara Ann Halkier,Caroline Müller

doi:10.1111/mpp.12672

Abstract

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. Agrobacterium 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 the camalexin biosynthesis pathway were up‐regulated, whereas genes in aliphatic glucosinolate (aGS) biosynthesis were generally down‐regulated, on 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 on transformation efficiency in Arabidopsis seedlings at the early infection stage. Later in the Agrobacterium infection process, the accumulation of camalexin is a key factor inhibiting tumour development on Arabidopsis inflorescence stalks. In conclusion, this study reveals the differential roles of GSs and camalexin at different stages of Agrobacterium‐mediated transformation and provides new insights into crown gall disease control and improvement of plant transformation.

Highlights

The plant pathogen Agrobacterium tumefaciens causes crown gall disease by a process initiated when A. tumefaciens senses phenolic compounds to induce the expression of virulence genes (Stachel et al, 1985)
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
Several genes involved in indole glucosinolate modification and the camalexin biosynthesis pathway were up-regulated, whereas genes in aliphatic glucosinolate biosynthesis were generally down-regulated, on Agrobacterium infection

Summary

Introduction

The plant pathogen Agrobacterium tumefaciens causes crown gall disease by a process initiated when A. tumefaciens senses phenolic compounds to induce the expression of virulence genes (Stachel et al, 1985). The transferred DNA (T-DNA) located on the tumour-inducing (Ti) plasmid is processed and transported from the bacterium into the plant cell. On T-DNA integration into the plant genome, the expression of T-DNA-encoded oncogenes causes the exogenous production of auxin and cytokinin to promote plant cell proliferation and lead to tumour formation. A. tumefaciens seems to be able to hijack host factors to promote T-DNA transfer and expression for crown gall development, plant defence and hormone response systems are quickly activated to counteract Agrobacterium infection.

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