Genetic complexity of pathogen perception by plants: the example of Rcr3, a tomato gene required specifically by Cf-2.

Genetic analysis of plant-pathogen interactions has demonstrated that resistance to infection is often determined by the interaction of dominant plant resistance (R) genes and dominant pathogen-encoded avirulence (Avr) genes. It was postulated that R genes encode receptors for Avr determinants. A large number of R genes and their cognate Avr genes have now been analyzed at the molecular level. R gene loci are extremely polymorphic, particularly in sequences encoding amino acids of the leucine-rich repeat motif. A major challenge is to determine how Avr perception by R proteins triggers the plant defense response. Mutational analysis has identified several genes required for the function of specific R proteins. Here we report the identification of Rcr3, a tomato gene required specifically for Cf-2-mediated resistance. We propose that Avr products interact with host proteins to promote disease, and that R proteins "guard" these host components and initiate Avr-dependent plant defense responses.

Genetic and molecular analysis of tomato Cf genes for resistance to Cladosporium fulvum.

In many plant-pathogen interactions resistance to disease is controlled by the interaction of plant-encoded resistance (R) genes and pathogen-encoded avirulence (Avr) genes. The interaction between tomato and the leaf mould pathogen Cladosporium fulvum is an ideal system to study the molecular basis of pathogen perception by plants. A total of four tomato genes for resistance to C. fulvum (Cf-2, Cf-4, Cf-5 and Cf-9) have been isolated from two genetically complex chromosomal loci. Their gene products recognize specific C. fulvum-encoded avirulence gene products (Avr2, Avr4, Avr5 and Avr9) by an unknown molecular mechanism. Cf genes encode extracellular membrane-anchored glycoproteins comprised predominantly of 24 amino acid leucine-rich repeats (LRRs). Cf genes from the same locus encode proteins which are more than 90% identical. Most of the amino-acid sequence differences correspond to the solvent-exposed residues within a beta-strand/beta-turn structural motif which is highly conserved in LRR proteins. Sequence variability within this motif is predicted to affect the specificity of ligand binding. Our analysis of Cf gene loci at the molecular level has shown they comprise tandemly duplicated homologous genes, and suggests a molecular mechanism for the generation of sequence diversity at these loci. Our analysis provides further insight into the molecular basis of pathogen perception by plants and the organization and evolution of R gene loci.

The tomato Cf-5 disease resistance gene and six homologs show pronounced allelic variation in leucine-rich repeat copy number.

The tomato Cf-2 and Cf-5 genes confer resistance to Cladosporium fulvum and map to a complex locus on chromosome 6. The Cf-5 gene has been isolated and is predicted to encode a largely extracytoplasmic protein containing 32 leucine-rich repeats (LRRs), resembling the previously isolated Cf-2 gene, which has 38 LRRs. Three haplotypes of this locus from Lycopersicon esculentum, L. pimpinellifolium, and L. esculentum var cerasiforme were compared, and five additional homologs of Cf-5 were sequenced. All share extensive sequence identity, particularly within the C-terminal portions of the predicted proteins. In striking contrast to the Cf-9 gene family, six of seven homologs in the Cf-2/Cf-5 gene family vary in LRR copy number, ranging from 25 to 38 LRRs. Cf-5 and one adjacent homolog differ by only two LRRs. Recombination events that vary the LRR copy number in this region could provide a mechanism for the generation of new specificities for recognition of different ligands. A recombination breakpoint between the Cf-2 and Cf-5 loci was fully characterized and shown to be intragenic.

The tomato Cf-2 disease resistance locus comprises two functional genes encoding leucine-rich repeat proteins.

In plants, resistance to pathogens is frequently determined by dominant resistance genes, whose products are proposed to recognize pathogen-encoded avirulence gene (Avr) products. The tomato resistance locus Cf-2 was isolated by positional cloning and found to contain two almost identical genes, each conferring resistance to isolates of tomato leaf mould (C. fulvum) expressing the corresponding Avr2 gene. The two Cf-2 genes encode protein products that differ from each other by only three amino acids and contain 38 leucine-rich repeat (LRR) motifs. Of the LRRs, 20 show extremely conserved alternating repeats. The C-terminus of Cf-2 carries regions of pronounced homology to the protein encoded by the unlinked Cf-9 gene. We suggest that this conserved region interacts with other proteins involved in activating plant defense mechanisms.

High-resolution mapping of the physical location of the tomato Cf-2 gene.

To isolate the tomato Cf-2 resistance gene by map-based cloning, plants recombinant for RFLP markers close to Cf-2 were selected by exploiting the flanking morphological markers yv (yellow virescent) and tl (thiaminless). Using these recombinants, a high-resolution linkage map of the region encompassing the Cf-2 gene has been generated containing several new RFLP markers. Mapping of two YAC clones carrying Lycopersicon esculentum and L. peruvianum DNA, indicates that in both genotypes the physical distance between the two closet flanking markers is less than 40 kb. This study also positions Cf-2 relative to the Mi gene, which confers resistance to root-knot nematodes.

RFLP linkage analysis of the Cf-4 and Cf-9 genes for resistance toCladosporium fulvum in tomato.

Four different populations segregating for one of the two closely linked (possibly allelic) tomato disease resistance genes to the fungusCladosporium fulvum,Cf-4 andCf-9, were generated and analysed for recombination frequencies between theCf-genes and restriction fragment length polymorphism (RFLP) loci. The population consisting of F2 progeny from the interspecific crossLycopersicon esculentum carryingCf-9 ×L. pennellii was identified as the most useful for RFLP mapping of theCf-4/9 locus and an RFLP map around this locus was constructed mainly using this population. The two closest markers identified were CP46, 2.6 cM distal, and a group of 11 markers including TG236, 3.7 cM proximal toCf-4/9. A polymerase chain reaction (PCR)-based procedure for the rapid identification of recombination events between these two markers was developed. The regions of foreign DNA introgression surroundingCf-4 andCf-9 in near-isogenic lines were delimited.

Tetanus following human bite.

We present an unusual case of tetanus which followed a human bite. The patient, a 43-year-old woman, developed tetanus within 4 days of sustaining a human bite. She died 6 days after admission despite aggressive management in the intensive care unit.

Acute haemodynamic effects of cromakalim in patients with angina pectoris.

1. We studied the acute haemodynamic effects of cromakalim, a vasodilator which activates smooth muscle potassium channels, in 11 patients with ischaemic heart disease undergoing routine cardiac catheterisation. A similar group of six patients given placebo were studied under identical conditions. 2. There were no significant differences in baseline haemodynamic parameters between the two groups. 3. Following intravenous cromakalim (15 micrograms kg-1) cardiac output increased by 30% (P less than 0.05 vs placebo) while systolic arterial pressure decreased by 8% (P less than 0.05), systemic vascular resistance decreased by 29% (P less than 0.01) and pulmonary vascular resistance decreased by 24% (P less than 0.01) at plasma concentrations of the (+)- and (-)-enantiomers of cromakalim of 6.2 +/- 0.5 ng ml-1 and 10.0 +/- 1.0 ng ml-1 respectively. 4. There were no significant differences in diastolic arterial pressure, left ventricular dP/dt and stroke volume between the two groups. Heart rate increased by 11% following cromakalim but this did not achieve significance. 5. These findings confirm that cromakalim acts primarily as an arteriolar vasodilator producing an improvement in cardiac performance. Cromakalim may be of benefit in the treatment of patients with ischaemic heart disease.

A randomized double-blind study of bisoprolol versus atenolol in mild to moderate essential hypertension.

We have compared the efficacy and pharmacokinetics of bisoprolol, a new cardioselective beta-adrenoceptor antagonist, with atenolol in a randomized double-blind crossover study in 12 patients (mean age 53.5 y) with mild to moderate essential hypertension. After a two week placebo wash-out period without any antihypertensive therapy, the patients were given bisoprolol 10 mg daily or atenolol 50 mg daily, increasing to 20 mg or 100 mg respectively if the sitting diastolic blood pressure did not fall below 90 mm Hg after two weeks of therapy. Crossover occurred after six weeks of active therapy followed by two weeks of placebo wash-out. After 6 weeks of therapy both drugs significantly reduced sitting and standing diastolic blood pressures (bisoprolol by 15% and 16% respectively, atenolol by 11% in both cases). However, while sitting and standing systolic pressures were significantly reduced by bisoprolol (13% and 16% respectively), only standing systolic pressures were significantly reduced by atenolol (11%), and this reduction was significantly less than with bisoprolol (p less than 0.05). Both drugs similarly reduced mean sitting and standing heart rates. There were no significant differences between the single-dose and steady-state kinetics of either bisoprolol or atenolol. The mean plasma elimination half-life (t1/2) increased from 12.9 to 13.2 h during steady state on bisoprolol and from 7.2 to 11.5 h on atenolol. The apparent volume of distribution (Vz) was greater for bisoprolol than for atenolol after single dosing (235 1 vs 146 1) and at steady state (216 1 vs 137 1), but clearances were similar for both drugs.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in the haemodynamic responses to exercise, posture and nitrates after treatment of congestive heart failure with an arteriolar vasodilator.

1. Haemodynamic responses to exercise, posture and nitrates were measured before and after 8 weeks of therapy with an arteriolar smooth muscle specific calcium antagonist, nicardipine, in eight patients with congestive heart failure (New York Heart Association class II or III). 2. The acute haemodynamic effects of intravenous nicardipine before and after 8 weeks of oral therapy confirmed its vasodilating properties, with similar end-points to the initial response after the 8 week period. 3. After 8 weeks of oral therapy all patients improved by one New York Heart Association class and treadmill exercise duration was significantly increased. In contrast, sitting bicycle exercise duration was not prolonged, although, at the same peak workload, changes in cardiac output, stroke volume and systemic vascular resistance were significantly improved after 8 weeks of therapy. 4. Sublingual glyceryl trinitrate predominantly affected pulmonary vascular resistance before and after chronic therapy with nicardipine, although the effects were less marked after 8 weeks. In contrast, the systemic vascular effects of glyceryl trinitrate were significantly increased after 8 weeks of therapy with nicardipine. 5. Increased vasodilator responses to sublingual glyceryl trinitrate and exercise after chronic treatment with nicardipine, in the absence of significant residual vasodilatation at rest, suggests that indirect changes in systemic arterioles may accompany and possibly contribute to the clinical improvement in heart failure.

Mesoderm-inducing properties of INT-2 and kFGF: two oncogene-encoded growth factors related to FGF.

Many theories of neoplasia suggest that oncogenic transformations result from aberrations in the control mechanisms which normally regulate growth and differentiation during embryonic development. It has recently become clear that many proto-oncogenes are differentially expressed during embryonic development and may thus be important embryonic regulatory molecules. We report here that the products of two transforming oncogenes int-2 and hst/ks (now called kfgf) can, with different potencies, induce mesoderm formation in isolated Xenopus laevis animal pole explants and stimulate DNA synthesis in mammalian fibroblasts. The results suggest that these proteins may function as mesoderm inducers in mammalian embryogenesis and that similar receptor/signalling pathways may be utilized for developmental and oncogenic processes. Finally, we have shown that the Xenopus assay system used in this study provides a powerful screen for protein factors that are active in development.

Syncope as the presentation of unstable angina.

A 71-year-old woman presented with syncope in association with unstable angina. Coronary angiography and subsequent postmortem findings demonstrated severe coronary arterial disease. The importance of the association of syncope with unstable angina and possible underlying mechanisms are discussed.

Severe fracture complications in myelodysplasia.

Prevention of fractures in the patient with myelodysplasia is aided by minimizing disuse osteoporosis by continuing weight-bearing whenever possible. The presentation and treatment of lower extremity fractures in the postoperative myelodysplasic patient have been reviewed. After these fractures severe systemic dysfunction can occur. A clinical situation involving hypovolemia and suggestive of fat embolism has responded well to immobilization in the posterior half of the spica cast and to fluid replacement.

Relationship of CSF shunting and IQ in children with myelomeningocele: a retrospective analysis.

This paper reviews 75 infants with myelomeningocele treated either at birth or from an early age at Rainbow Babies and Children's Hospital, for whom complete records and psychometric testing (IQ) are available (including complete summaries from referring hospitals). Three groups are compared: (1) infants without complications who were shunted for hydrocephalus (n = 41); (2) infants with complications who were shunted (n = 16), and (3) infants who were not shunted (n = 18). Complications were defined as ventriculitis (positive CSF cultures with elevated protein, depressed glucose and inflammatory cells), anoxia, poorly controlled hydrocephalus or other CNS anomalies such as porencephaly. The mean IQ of infants who were not shunted was 104, of those shunted without complications it was 91, and of those shunted who had complications it was 70. These IQ differences were significant at p less than 0.01, and were not explained by differences in spinal lesion levels.

Correlations between ancillary assays and bacteriuria in children with myelodysplasia and ileal conduit urinary diversions.

Urine from children with ileal conduit urinary diversions was assayed for antibody-coated bacteria, lysozyme and lactic dehydrogenase isoenzymes, and correlated with the results of quantitative urine culture. A significant proportion of the antibody-coated bacteria and lysozyme assays were positive when more than 10(4) organisms per ml. of urine were found. Lactic dehydrogenase isoenzyme results were frequently at variance with the other assay and culture results. Because none of the ancillary assays was invariably positive in patients with symptoms suggestive of upper tract disease, they remain imperfect research tools for localization of urinary tract infections in patients with ileal conduits. In this patient population quantitative urine culture remains the best clinical method for diagnosing urinary tract infections and evaluating the adequacy of antibiotic therapy. However, since the antibody-coated bacteria and lysozyme assays converted to negative with successful treatment, these tests may provide additional guidance to the physician in assessing the adequacy of treatment of urinary tract infections in patients with ileal conduit diversions.

Vertebral agenesis: comprehensive care and outcome.

There is little information concerning long-term outcome of vertebral agenesis. In this series of eight patients with variable severity of vertebral agenesis, three died during infancy, two of associated congenital anomalies involving the cardiorespiratory system and one of unknown causes. The remaining five have had no life-threatening problems. They have normal intellect, and the developmental achievements are adequate for their age. The five patients with the highest lesions were those born to diabetic mothers. We also discuss current concepts of comprehensive team management of such infants.