Systemic gene expression in arabidopsis during an incompatible interaction with Alternaria brassicicola

Pathogen challenge can trigger an integrated set of signal transduction pathways, which ultimately leads to a state of high alert, otherwise known as systemic or induced resistance in tissue remote to the initial infection. Although large-scale gene expression during systemic acquired resistance, which is induced by salicylic acid or necrotizing pathogens has been previously reported using a bacterial pathogen, the nature of systemic defense responses triggered by an incompatible necrotrophic fungal pathogen is not known. We examined transcriptional changes that occur during systemic defense responses in Arabidopsis plants inoculated with the incompatible fungal pathogen Alternaria brassicicola. Substantial changes (2.00-fold and statistically significant) were demonstrated in distal tissue of inoculated plants for 35 genes (25 up-regulated and 10 down-regulated), and expression of a selected subset of systemically expressed genes was confirmed using real-time quantitative polymerase chain reaction. Genes with altered expression in distal tissue included those with putative functions in cellular housekeeping, indicating that plants modify these vital processes to facilitate a coordinated response to pathogen attack. Transcriptional up-regulation of genes encoding enzymes functioning in the beta-oxidation pathway of fatty acids was particularly interesting. Transcriptional up-regulation was also observed for genes involved in cell wall synthesis and modification and genes putatively involved in signal transduction. The results of this study, therefore, confirm the notion that distal tissue of a pathogen-challenged plant has a heightened preparedness for subsequent pathogen attacks.

Survey of ferroxidase expression and siderophore production in clinical isolates of Pseudomonas aeruginosa

Ferroxidase (encoded by the mco gene), a component of a ferrous iron uptake pathway in Pseudomonas aeruginosa, was detected in all of the 35 respiratory clinical isolates surveyed; in contrast, considerable variation in siderophore expression was observed. The ubiquitous expression of this periplasmic ferroxidase suggests that it plays a key role in iron uptake in this opportunistic pathogen.

Characterization of a complex chemosensory signal transduction system which controls twitching motility in Pseudomonas aeruginosa

Virulence of the opportunistic pathogen Pseudomonas aeruginosa involves the coordinate expression of a wide range of virulence factors including type IV pili which are required for colonization of host tissues and are associated with a form of surface translocation termed twitching motility. Twitching motility in P. aeruginosa is controlled by a complex signal transduction pathway which shares many modules in common with chemosensory systems controlling flagella rotation in bacteria and which is composed, in part, of the previously described proteins PilG, PilH, PilI, PilJ and PilK. Here we describe another three components of this pathway: ChpA, ChpB and ChpC, as well as two downstream genes, ChpD and ChpE, which may also be involved. The central component of the pathway, ChpA, possesses nine potential sites of phosphorylation: six histidine-containing phosphotransfer (HPt) domains, two novel serine- and threonine-containing phosphotransfer (SPt, TPt) domains and a CheY-like receiver domain at its C-terminus, and as such represents one of the most complex signalling proteins yet described in nature. We show that the Chp chemosensory system controls twitching motility and type IV pili biogenesis through control of pili assembly and/or retraction as well as expression of the pilin subunit gene pilA. The Chp system is also required for full virulence in a mouse model of acute pneumonia.

Enhanced clearance of Candida albicans from the oral cavities of mice following oral administration of Lactobacillus acidophilus

Orally administered live Lactobacillus acidophilus was assessed for its capacity to enhance clearance from the oral cavity of DBA/2 mice shown previously to be 'infection prone'. L. acidophilus fed to DBA/2 mice significantly shortened the duration of colonization of the oral cavity compared to controls. Enhanced clearance of Candida albicans correlated with both early mRNA gene expression for interleukin (IL)-4 and interferon (IFN)-gamma and expression of their secreted products in cultures of cervical lymph nodes stimulated with Candida antigen. In addition rapid clearance correlated with higher levels of IFN-gamma and nitric oxide in saliva. Delayed clearance, less pronounced levels of the cytokine response, saliva IFN-gamma and nitric oxide, and later mRNA expression for IL-4 and IFN-gamma relative to feeding with the L. acidophilus isolate were noted in mice fed a different Lactobacillus isolate (L. fermentum). These observations indicate significant variations in individual isolates to activate the common mucosal system.

Isolates of Candida albicans that differ in virulence for mice elicit strain-specific antibody-mediated protective responses

Three distinct isolates of Candida albicans were used to establish systemic and oral infections in inbred mice that are genetically resistant or susceptible to tissue damage. Patterns of infection differed significantly between both yeasts and mouse strains. Systemic infection conferred significant protection against re-challenge with the homologous, but not the heterologous yeast; however, the protective effect was more evident in the tissue-susceptible CBA/CaH mice than in the resistant BALB/c strain. In contrast, oral infection induced protection against both homologous and heterologous oral challenge, although this was significant only in the CBA/CaH mice. CBA/CaH mice produced antibodies of both IgG1 and IgG2a subclasses, whereas BALB/c mice produced predominantly IgG1. Western blotting demonstrated considerable differences between epitopes recognised by serum antibodies from mice of both strains after immunisation with each of the three yeasts. Thus, different strains of yeast show considerable specificity in antibody responses elicited by either systemic or oral infection. (c) 2005 Elsevier SAS. All rights reserved.

Nucleolar localization of aprataxin is dependent on interaction with nucleolin and on active ribosomal DNA transcription

The APTX gene, mutated in patients with the neurological disorder ataxia with oculomotor apraxia type 1 (AOA1), encodes a novel protein aprataxin. We describe here, the interaction and interdependence between aprataxin and several nucleolar proteins, including nucleolin, nucleophosmin and upstream binding factor-1 (UBF-1), involved in ribosomal RNA (rRNA) synthesis and cellular stress signalling. Interaction between aprataxin and nucleolin occurred through their respective N-terminal regions. In AOA1 cells lacking aprataxin, the stability of nucleolin was significantly reduced. On the other hand, down-regulation of nucleolin by RNA interference did not affect aprataxin protein levels but abolished its nucleolar localization suggesting that the interaction with nucleolin is involved in its nucleolar targeting. GFP-aprataxin fusion protein co-localized with nucleolin, nucleophosmin and UBF-1 in nucleoli and inhibition of ribosomal DNA transcription altered the distribution of aprataxin in the nucleolus, suggesting that the nature of the nucleolar localization of aprataxin is also dependent on ongoing rRNA synthesis. In vivo rRNA synthesis analysis showed only a minor decrease in AOA1 cells when compared with controls cells. These results demonstrate a cross-dependence between aprataxin and nucleolin in the nucleolus and while aprataxin does not appear to be directly involved in rRNA synthesis its nucleolar localization is dependent on this synthesis.