A Eucalyptus bacterial wilt isolate from South Africa is pathogenic on Arabidopsis and manipulates host defences

Abstract

Summary Ralstonia solanacearum, the causal agent of bacterial wilt, has been reported from Eucalyptus plantations in at least three countries in Africa. The lack of genomics resources in Eucalyptus species led us to develop and study a pathosystem between a previously characterized South African isolate and the model plant Arabidopsis thaliana. Ralstonia solanacearum BCCF401 isolated from a Eucalyptus grandis × Eucalyptus camaldulensis hybrid was shown to cause disease on A. thaliana ecotype Col‐5. Arabidopsis genomics tools were exploited to investigate gene expression changes during wilt disease development, and thereby develop hypotheses that can be tested in Eucalyptus once genomics resources are available. Transcriptome analysis using 5000 A. thaliana ESTs was performed and revealed 141 genes that were differentially regulated by R. solanacearum infection (at a significance threshold of p < 0.03; Bonferroni corrected). A software tool ‘Rank Correlation Comparer’ was developed to compare expression profiles with Arabidopsis Affymetrix NASCArray data. High correlations were observed between the response of Arabidopsis plants to both Eucalyptus (BCCF401) and tomato (GMI1000) isolates of R. solanacearum, as well as to Pseudomonas syringae, Botrytis cinerea and treatment with abscisic acid. Basal defence responses in Col‐5 in response to R. solanacearum were investigated by comparing the expression data following R. solanacearum infection to data after treatment with the Pathogen Associated Molecular Patterns (PAMP) flg22 and lipopolysaccharide, and the Type Three Secretion System deficient Pseudomonas syringae pv. tomato hrp− mutant. A subset of the genes which were induced by PAMPs were repressed by R. solanacearum infection, and vice versa, suggesting that these genes may be repressed or induced, respectively, by specific R. solanacearum effectors. We hypothesize that these genes represent targets of R. solanacearum effectors. The pending release of the Eucalyptus genome sequence will enable orthologues to be identified and these hypotheses to be tested in Eucalyptus trees.

Gene-for-Gene Tolerance to Bacterial Wilt in Arabidopsis

“…Interestingly, the A. thaliana ein2.1 mutant, which is defective in ethylene signaling, exhibits a phenotype reminiscent of tolerance because, despite a delayed symptom development, it supports high bacterial multiplication . Microarray expression profiling of susceptible responses of A. thaliana accessions to R. solanacearum strains has been reported (Hu et al 2008;Naidoo et al 2011). It would be interesting to compare expression profiles from tolerant and susceptible plants that both support high bacterial numbers but differ in symptom development.…”

“…solanacearum biovar 3 phylotype I strain BCCF402 (Fouché-Weich et al 2006;Roux et al 2000) was grown on solidified bacto-agar glucose triphenyltetrazolium chloride (BGT) medium at 28°C for 48 h and mucoid colonies were transferred to liquid B medium (Deslandes et al 1998). Rifampicin mutants were prepared as described previously (Naidoo et al 2011).…”

“…Preparation of the BCCF402 Δhrp mutant was conducted as described for BCCF401 (Naidoo et al 2011) using genomic DNA from Δhrp R. solanacearum GMI1402, a derivative of GMI1000 carrying a disruption in the hrcS (hrp-conserved) gene (Arlat et al 1992). BCCF402 Δhrp mutants that were unable to induce a hypersensitive response on tobacco were selected (data not shown).…”

“…We previously reported that R. solanacearum BCCF401, collected from Eucalyptus grandis × E. camaldulensis plantations in South Africa (Fouché-Weich et al 2006), was pathogenic on Arabidopsis accession Col-0 (Naidoo et al 2011). In the current study, we characterized the response of Arabidopsis accessions to another Eucalyptus strain of R. solanacearum called BCCF402.…”

Enfermedades bacterianas de eucaliptos: Estado actual del conocimiento

“…La investigación debería enfocarse en el corto plazo en el control biológico de estas enfermedades en vivero, ya que hay evidencias de experiencias promisorias en mancha foliar (Marcolin et al 2015) y en marchitamiento vascular (Ran et al 2005). También la manipulación genética, como lo mencionan Naidoo et al (2011) como posible estrategia de control de Ralstonia solanacearum, se ha convertido en un enfoque innovador poco explorado hasta la fecha.…”