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Global gene expression analysis of the heat shock response in the phytopathogen Xylella fastidiosa

ABSTRACT: Xylella fastidiosa is a phytopathogenic bacterium responsible for diseases in many economically important crops. Although different strains have been studied, little is known about X. fastidiosa stress responses. One of the best characterized stresses in bacteria is the heat shock response, which induces the expression of specific genes to prevent protein misfolding and aggregation, and to promote degradation of the irreversibly denatured polypeptides. To investigate X. fastidiosa genes involved in the heat shock response, we performed a whole genome microarray analysis in a time-course experiment. Globally, 261 genes were induced (9.7%) and 222 genes were repressed (8.3%). The expression profiles of the differentially expressed genes were grouped and their expression patterns were validated by quantitative RT-PCR experiments. As expected, genes that presented the higher induction rates encoded chaperones and proteases. We determined the transcription start site of six heat shock inducible genes and analyzed their promoter regions, which allowed us to propose a putative consensus for 32 promoters in Xylella and suggest additional genes as putative members of this regulon. Besides the induction of classical heat shock protein genes, we observed the up-regulation of virulence-associated genes such as vapD, hemagglutinins, hemolysin and xylan degrading enzymes, which may indicate the importance of heat stress to bacterial pathogenesis. In addition, we observed the repression of genes related to fimbriae, aerobic respiration, protein biosynthesis, and the induction of genes related to the extracytoplasmic stress response and some phage-related genes, revealing the complex network of genes that work together in response to heat shock. Keywords: stress response; heat shock response

ORGANISM(S): Xylella fastidiosa

PROVIDER: GSE4161 | GEO | 2006/06/01

SECONDARY ACCESSION(S): PRJNA95077

REPOSITORIES: GEO

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Project description:Xylella fastidiosa is the etiologic agent of a wide range of plant diseases including citrus variegated chlorosis (CVC), a major threat to the Brazilian citrus industry. Genome sequences of several strains of this phytopathogen are accessible, enabling large-scale functional studies. Transcript levels in different iron availabilities were assessed with DNA microarrays representing 2608 (91.6%) coding sequences (CDS) of X. fastidiosa CVC strain 9a5c. When treated with the iron chelator 2,2-dipyridyl, 193 CDS were considered as up-regulated and 216 as down-regulated. In the presence of 100uM of ferric pyrophosphate, 218 and 256 CDS were considered as up- and down-regulated, respectively. Differential expression for a subset of 44 CDS was further evaluated by reverse transcription - quantitative PCR that showed a Pearson correlation of 0.77 with array results. The CDS differentially expressed upon the iron concentration shift participate in diverse cellular functions. Many CDS involved with regulatory functions, pathogenicity and cell structure, were modulated in both conditions tested suggesting that major changes in cell architecture and metabolism occur when X. fastidiosa cells are exposed to extreme variations in iron concentration. Interestingly, the modulated CDS include those related to colicin V-like bacteriocin synthesis and secretion and to pili/fimbriae functions. We also investigated the contribution of the ferric uptake regulator Fur to the iron regulon of X. fastidiosa. The promoter regions of strain 9a5c genome were screened for putative Fur boxes and candidates were analyzed by electrophoretic mobility shift assays. Taken together, our data support the hypothesis that Fur is not solely responsible for the modulation of the iron regulon of X. fastidiosa and present novel evidence for iron regulation of pathogenicity determinants. Keywords: stress response; response to iron-depleted condition Direct comparison between low iron content (200uM 2,2-dipyridyl) and control condition. Hybridizations are dye-swaped. There are 2 biological replicates (independent harvest) and 2 technical replicates of each array (L - left and R - right).

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Global gene expression analysis of the heat shock response in the phytopathogen Xylella fastidiosa

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