Plant NLRs with Integrated Domains: Unity Makes Strength

Integration of unusual domains in plant immune receptors is a widespread mechanism of NLR diversification enabling specific pathogen detection.

Fungal model systems and the elucidation of pathogenicity determinants

Fungi have the capacity to cause devastating diseases of both plants and animals, causing significant harvest losses that threaten food security and human mycoses with high mortality rates. As a consequence, there is a critical need to promote development of new antifungal drugs, which requires a comprehensive molecular knowledge of fungal pathogenesis. In this review, we critically evaluate current knowledge of seven fungal organisms used as major research models for fungal pathogenesis. These include pathogens of both animals and plants; Ashbya gossypii, Aspergillus fumigatus, Candida albicans, Fusarium oxysporum, Magnaporthe oryzae, Ustilago maydis and Zymoseptoria tritici. We present key insights into the virulence mechanisms deployed by each species and a comparative overview of key insights obtained from genomic analysis. We then consider current trends and future challenges associated with the study of fungal pathogenicity.

Utilization of quinate and p-hydroxybenzoate by actinomycetes: key enzymes and taxonomic relevance

474 strains of the actinomycete genera Streptomyces (including species of the former genera Chainia and Streptoverticillium), Pseudonocardia and Micromonospora were examined for their ability to degrade quinate (Q) and p-hydroxybenzoate (pHB); selected strains were also tested for their capacity to catabolize benzoate (B). Whereas in the case of Q (5-10 g/l of a mineral salts agar medium) the growth response signalizes assimilation, pHB has to be supplied in lower concentration (routinely 0.3 g/l together with small amounts of peptone and yeast extract in liquid broth), and its degradation has to be determined spectrophotometrically. 27% of the streptomycete strains were able to grow with Q, and 57% with pHB. The three strains of "Chainia" that were tested metabolized Q and pHB, but none of the fourty species of "Streptoverticillium" showed this ability. 80% of the 30 strains of Psn. autotrophica grew with Q, and 100% degraded pHB and B. Two of the five Micromonospora strains gave a positive response with pHB, but not with Q.-Toluene treated cells (preincubated with Q, pHB or B, respectively) gave a positive Rothera reaction with protocatechuate or catechol respectively, thus demonstrating that these organisms employed the beta-ketoadipate pathway (orthofission) for the degradation of Q, pHB and B. The assay of five relevant enzymes in cell-free extracts of nine selected organisms showed that in nocardioform actinomycetes (Pseudonocardia, Rhodococcus) all enzymes of the protocatechuate branch of the ketoadipate pathway seem to be induced by beta-ketoadipate as demonstrated here for protocatechuate-3,4-dioxygenase. In contrast, in Streptomyces this enzyme appears to be induced by its substrate, protocatechuate, whereas the regulation of the other enzymes of this pathway remains to be elucidated.

Cloning and sequence analysis of genes for dehalogenation of 4-chlorobenzoate from Arthrobacter sp. strain SU

Strains of Arthrobacter catalyze a hydrolytic dehalogenation of 4-chlorobenzoate (4-CBA) to p-hydroxybenzoate. The reaction requires ATP and coenzyme A (CoA), indicating activation of the substrate via a thioester, like that reported for Pseudomonas sp. strain CBS3 (J. D. Scholten, K.-H. Chang, P. C. Babbit, H. Charest, M. Sylvestre, and D. Dunaway-Mariano, Science 253:182-185, 1991). The dehalogenase genes of Arthrobacter sp. strain SU were cloned and expressed in Escherichia coli. Analyses of deletions indicate that dehalogenation depends on three open reading frames (ORFs) which are organized in an operon. There is extensive sequence homology to corresponding gene products in Pseudomonas sp. strain CBS3, suggesting that ORF1 and ORF2 encode a 4-CBA-CoA-ligase and a 4-CBA-CoA dehalogenase, respectively. ORF3 possibly represents a thioesterase, although no homology to the enzyme from Pseudomonas sp. strain CBS3 exists.

Naphthalene degradation via salicylate and gentisate by Rhodococcus sp. strain B4

Rhodococcus sp. strain B4, isolated from a soil sample contaminated with polycyclic aromatic hydrocarbons, grows with naphthalene as the sole source of carbon and energy. Salicylate and gentisate were identified as intermediates in the catabolism of naphthalene. In contrast to the well-studied catabolic pathway encoded by the NAH7 plasmid of Pseudomonas putida, salicylate does not induce the genes of the naphthalene-degradative pathway in Rhodococcus sp. strain B4. The key enzymes of naphthalene degradation in Rhodococcus sp. strain B4 have unusual cofactor requirements. The 1,2-dihydroxynaphthalene oxygenase activity depends on NADH and the salicylate 5-hydroxylase requires NADPH, ATP, and coenzyme A.

Construction of a hybrid plasmid capable of replication in Amycolatopsis mediterranei

A new plasmid, pA387, has been isolated from "Amycolatopsis sp." (DSM 43387). This plasmid could be isolated from liquid culture as well as mycelium from agar plates by a modified procedure. Plasmid pA387 is about 29.6 kb and can be cured at low frequency by protoplasting and ethidium bromide and heat treatment. Hybridization experiments showed that this plasmid is present in free form and does not integrate into the chromosome. A hybrid plasmid was constructed by cloning a 5.1-kb fragment of pA387 into the Escherichia coli vector pDM10. This hybrid plasmid, termed pRL1, could be transformed into Amycolatopsis mediterranei and A. orientalis by electroporation. A transformation frequency of 2.2 x 10(3) transformants per micrograms of DNA at 12.5 kV/cm and a pulse duration of 10.8 ms was obtained in A. mediterranei, whereas 1.1 x 10(5) transformants per microgram of DNA were obtained at a field strength of 7.5 kV/cm and a pulse duration of 7.6 ms in A. orientalis. Plasmid pRL1 is the first hybrid plasmid which could be used successfully for the transformation of A. mediterranei. The plasmid has a rather high copy number, is genetically stable, and can be easily reisolated from A. mediterranei. Plasmid pRL1 will be useful for further construction of a shuttle vector for E. coli and A. mediterranei and becomes the basis for the development of gene cloning techniques in Amycolatopsis spp.

Catabolism of benzoate and monohydroxylated benzoates by Amycolatopsis and Streptomyces spp

Eight actinomycetes of the genera Amycolatopsis and Streptomyces were tested for the degradation of aromatic compounds by growth in a liquid medium containing benzoate, monohydroxylated benzoates, or quinate as the principal carbon source. Benzoate was converted to catechol. The key intermediate in the degradation of salicylate was either catechol or gentisate, while m-hydroxybenzoate was metabolized via gentisate or protocatechuate. p-Hydroxybenzoate and quinate were converted to protocatechuate. Catechol, gentisate, and protocatechuate were cleaved by catechol 1,2-dioxygenase, gentisate 1,2-dioxygenase, and protocatechuate 3,4-dioxygenase, respectively. The requirement for glutathione in the gentisate pathway was dependent on the substrate and the particular strain. The conversion of p-hydroxybenzoate to protocatechuate by p-hydroxybenzoate hydroxylase was gratuitously induced by all substrates that were metabolized via protocatechuate as an intermediate, while protocatechuate 3,4-dioxygenase was gratuitously induced by benzoate and salicylate in two Amycolatopsis strains.

Preliminary characterization of a group of actinophages of the thermophilic actinomycete genus Saccharomonospora

The comparison of the Saccharomonospora phages phi SaC1, phi SaG1, phi SaV1, phi SaV2, phi SaV3, and Tm1 demonstrated that they all belong to a single group of closely related actinophages: they were similar with regard to host range, virion mophology (B1 type), genome length (43-45 kb), and GC content of their genomes (63, 3% G + C). Furthermore, DNA-DNA hybridization showed that the phage genomes had a high degree of homology to each other. The phages are, therefore, proposed as representatives of a new bacteriophage species in the sense of the ICTV.

Structural determination of a new naturally occurring cyclic vitamin K

The respiratory quinone composition of 5 members of the genus Nocardia was examined. All species contained a hitherto unknown cyclic vitamin K-like molecule as their predominant lipoquinone. On the basis of mass spectrometry, 1H and 13C nuclear magnetic resonance spectrometry, the novel quinone was shown to correspond to (2E, 14E, 18E, 22E)-2-[3,7, 11,15,19,23-hexamethyl-25-(2,6,6-trimethylcyclohex-2- enyl)pentacosa-2, 14,18,22-tetraenyl]-3-methyl-1,4-naphthoquinone. Results indicate this molecule may represent a valuable phylogenetic marker for the prokaryote genus Nocardia.

Reduced induction of pyruvate kinase after feeding 2-acetylaminofluorene

After administration of carcinogens to laboratory animals reduced induction of some enzymes has been found which is believed to be associated with the carcinogenic process. It is suggested that this effect may be used for the testing of chemical substances for carcinogenicity. For this purpose the dietary induction of pyruvate kinase in rat liver was investigated after feeding 2-acetylaminofluorene. The induced activity in the animals fed the carcinogen was found to be significantly lower than in the control, however, the extent of this reduction was too low to be used for testing chemical substances for carcinogenicity.

Effect of carotid pressoreceptor stimulation on integrated systemic venous bed

In 9 mongrel dogs, venous return was completely drained from the caval veins to an oxygenator and returned to the femoral arteries with a roller pump. Perfusion rate of systemic circulation and blood pressures in both caval veins were kept constant. Changes in the oxygenator weight were recorded and reflected reciprocal changes in integrated systemic venous blood volume. The vagal nerves were dissected. The carotid sinuses were separately perfused with blood by means of a pump. In 25 experiments, increases in carotid sinus pressure of 15 to 74 mm Hg resulted in decreases in systemic arterial pressure of 10 to 57 mm Hg and increases in systemic venous blood volume of 1.1 to 4.7 ml/kg. On an average, systemic venous blood volume was changed by 1.25 +/- 0.08 ml/kg when the change in systemic arterial pressure was 10 mm Hg. It is concluded that the carotid sinus pressoreceptor reflex considerably alters the systemic venous capacity which in tern alters venous return and cardiac output. These changes in cardiac output are expected to be small, but sufficient to alter the arterial pressure considerably. Thus, they might contribute nearly as much as the reflex effect on total peripheral resistance to the reflex control of arterial pressure.

Use of human-liver microsomes from kidney-transplant donors for the induction of chromatid aberrations and sister-chromatid exchanges by means of pre-carcinogens in Chinese hamster cells in vitro

Samples of two human livers taken during operation of kidney donor patients were processed for microsome fractions and used for metabolization of cyclophosphamide (CP) and dimethylnitrosamine (DMN) in combination with the NADPH-generating system. Rat-liver microsomes were checked for comparison. Induction of chromatid aberrations and sister-chromatid exchanges in a newly isolated clone of Chinese hamster fibroblasts served as indicators of activity. Human S-9 fractions standardized on protein content showed strong variations of CP and DMN activation. Whereas liver microsomes of one patient (who also suffered from Gaucher's disease) were highly active for both pre-carcinogens and metabolized DMN at the same level as the uninduced rat-liver microsomes, the S-9 fraction from the second patient failed to activate CP, but was distinctly positive for DMN. It is suggested that samples of liver and other organs of renal transplant donors might be a practicable source of freshly prepared human microsome fractions usable in biochemical, genetic and carcinogenetic studies. Problems concerning the extrapolation of results are discussed.