Abstract:
Ralstonia solanaearum, a soil borne pathogen infects several important crops causing wilting. In 2000-2001, two eucalyptus isolates, BCCF 401 and BCCF 402 were isolated from plantations in Kwa-Zulu Natal and the Democratic Republic of Congo, respectively. Arabidopsis has been recognised as a host for R. solanacearum and as such has been adopted as a model to understand the plant defence response against this pathogen. The aim of this study was to use microarray expression profiling techniques to elucidate the plant defence response and to identify candidate genes possibly contributing towards resistance against the pathogen. As a means to optimise microarray expression profiling, the differential expression in an Arabidopsis mutant, cir1 (constitutively induced resistance 1) and wild-type plants was investigated using a custom 500-probe microarray. Several genes were found to be induced in cir1 at a significance threshold of –log10(p) equal to 3 (p< 0.001) using a mixed model ANOVA approach. The genes AtACP1 (sodium inducible calcium binding protein), AtP2CHA (protein phosphatase 2C), AtGSTF7 (glutathione S transferase), tryptophan synthase betalike and AtPAL1 (phenylalanine ammonia lyase 1), AtEREBP-4 (ethylene response element binding protein 4) and HFR1 (long hypocotyl in far-red 1) were further identified as possible candidate genes which may contribute to disease resistance in cir1 against Pseudomonas syringae pv. tomato. A similar transcript profiling approach, using the optimised protocols, was adopted to investigate the compatible interaction between Arabidopsis ecotype Col-5 and the R. solanacearum isolate BCCF 401. A screen of 5000 Arabidopsis ESTs revealed approximately 120 genes differentially regulated by R. solanacearum infection at a significance threshold of p<0.03 (Bonferroni corrected). Subsequent bioinformatic comparisons revealed that abscisic acid responses appear to be induced in Col-5 in response to the pathogen and that R. solanacearum induces an expression profile consistent with a necrotroph. The basal defence responses in Col-5 against R. solanacearum infection were investigated by comparing the expression data to that during treatment with the pathogen associated molecular patterns (PAMPs) flg22 and lipopolysaccharide, and the Type Three Secretion System deficient Pst hrp- mutant. Expression patterns for a subset of these genes were suggestive of host basal defences manipulated by the pathogen. It is hypothesised that genetic engineering to alter the expression of these “pathogen-manipulated” genes could contribute to resistance against R. solanacearum in the host. Copyright 2008, University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. Please cite as follows: Naidoo, S 2008, Microarray expression studies in the model plant Arabidopsis thaliana infected with the bacterial pathogen Ralstonia solanacearum, PhD thesis, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-11182008-092625 / > D559/gm
