The calcium-permeable channel OSCA1.3 regulates plant stomatal immunity

Perception of biotic and abiotic stresses often leads to stomatal closure in plants 1,2. Rapid influx of calcium ions (Ca 2+) across the plasma membrane has an important role in this response, but the identity of the Ca 2+ channels involved has remained elusive 3,4. Here we report that the Arabidopsis thaliana Ca 2+-permeable channel OSCA1.3 controls stomatal closure during immune signalling. OSCA1.3 is rapidly phosphorylated upon perception of pathogen-associated molecular patterns (PAMPs). Biochemical and quantitative phosphoproteomics analyses reveal that the immune receptor-associated cytosolic kinase BIK1 interacts with and phosphorylates the N-terminal cytosolic loop of OSCA1.3 within minutes of treatment with the peptidic PAMP flg22, which is derived from bacterial flagellin. Genetic and electrophysiological data reveal that OSCA1.3 is permeable to Ca 2+, and that BIK1-mediated phosphorylation on its N terminus increases this channel activity. Notably, OSCA1.3 and its phosphorylation by BIK1 are critical for stomatal closure during immune signalling, and OSCA1.3 does not regulate stomatal closure upon perception of abscisic acid—a plant hormone associated with abiotic stresses. This study thus identifies a plant Ca 2+ channel and its activation mechanisms underlying stomatal closure during immune signalling, and suggests specificity in Ca 2+ influx mechanisms in response to different stresses

Antimicrobial susceptibility of Shigella flexneri and S. dysenteriae isolated from stool specimens of patients with bloody diarrhoea in Mwansa, Tanzania

No Abstract. Tanzania Health Research Bulletin Vol. 9 (3) 2007: pp.186-18

Antimicrobial susceptibility of Shigella flexneri and S. dysenteriae isolated from stool specimens of patients with bloody diarrhoea in Mwanza, Tanzania

This study was conducted to determine frequency and pattern of antimicrobial susceptibility of Shigella species isolated from stool specimens collected from patients presenting with bloody diarrhoea in Mwanza City, Tanzania. The study was carried out from October 2004 to October 2005 and involved patients attending Sekou Toure Regional Hospital and Butimba Health Centre. Bacteriological cultures were done at the National Institute for Medical Research laboratory. A total of 489 patients (median age= 20 years) participated in the study and were able to provide stool specimens. Shigella species were isolated from 14% (69/489) of the stool specimens collected. Of the sixty nine strains of Shigella isolated, 62 (90%) were S. flexneri and 7 (10%) were S. dysenteriae. All Shigella strains isolated showed high resistance to ampicillin, tetracycline, trimethoprim-sulphamethoxazole and chloramphenicol, drugs commonly used for management of shigellosis in Tanzania. However all isolates were fully susceptible to ciprofloxacin, nalidixic acid, erythromycin, cefuroxime and gentamycin. S. flexneri showed resistance to amoxy-clavulanicacid and azithromycin in 5% and 2% of isolates, respectively. None of the S. dysenteriae isolates were resistant to these two drugs. Entamoeba histolytica   , Giardia lamblia   and Schistosoma mansoni   were microscopically detected in 16.5%, 4.4% and 5.3 % of patients, respectively These findings suggest that there is a need to carry out extensive susceptibility studies in different parts of the country with view of re-appraising the current guidelines for management of bloody diarrhoea in Tanzania

The calcium-permeable channel OSCA1.3 regulates plant stomatal immunity

Perception of biotic and abiotic stresses often leads to stomatal closure in plants1,2. Rapid influx of calcium ions (Ca2+) across the plasma membrane has an important role in this response, but the identity of the Ca2+ channels involved has remained elusive3,4. Here we report that the Arabidopsis thaliana Ca2+-permeable channel OSCA1.3 controls stomatal closure during immune signalling. OSCA1.3 is rapidly phosphorylated upon perception of pathogen-associated molecular patterns (PAMPs). Biochemical and quantitative phosphoproteomics analyses reveal that the immune receptor-associated cytosolic kinase BIK1 interacts with and phosphorylates the N-terminal cytosolic loop of OSCA1.3 within minutes of treatment with the peptidic PAMP flg22, which is derived from bacterial flagellin. Genetic and electrophysiological data reveal that OSCA1.3 is permeable to Ca2+, and that BIK1-mediated phosphorylation on its N terminus increases this channel activity. Notably, OSCA1.3 and its phosphorylation by BIK1 are critical for stomatal closure during immune signalling, and OSCA1.3 does not regulate stomatal closure upon perception of abscisic acid-a plant hormone associated with abiotic stresses. This study thus identifies a plant Ca2+ channel and its activation mechanisms underlying stomatal closure during immune signalling, and suggests specificity in Ca2+ influx mechanisms in response to different stresses

Oomycete pathogens encode RNA silencing suppressors

Effectors are essential virulence proteins produced by a broad range of parasites, including viruses, bacteria, fungi, oomycetes, protozoa, insects and nematodes. Upon entry into host cells, pathogen effectors manipulate specific physiological processes or signaling pathways to subvert host immunity. Most effectors, especially those of eukaryotic pathogens, remain functionally uncharacterized. Here, we show that two effectors from the oomycete plant pathogen Phytophthora sojae suppress RNA silencing in plants by inhibiting the biogenesis of small RNAs. Ectopic expression of these Phytophthora suppressors of RNA silencing enhances plant susceptibility to both a virus and Phytophthora, showing that some eukaryotic pathogens have evolved virulence proteins that target host RNA silencing processes to promote infection. These findings identify RNA silencing suppression as a common strategy used by pathogens across kingdoms to cause disease and are consistent with RNA silencing having key roles in host defense