Diversity,structure, and synteny of the cutinase gene of Colletotrichum species

Colletotrichum species complexes are among the top 10 economically important fungal plant pathogens worldwide because they can infect climacteric and nonclimacteric fruit at the pre and/or postharvest stages. C. truncatum is the major pathogen responsible for anthracnose of green and red bell pepper fruit worldwide. C. brevisporum was recently reported to be a minor pathogen of red bell pepper fruit in Trinidad, but has recently been reported as pathogenic to other host species in other countries. The ability of these phytopathogens to produce and secrete cutinase is required for dismantling the cuticle of the host plant and, therefore, crucial to the necrotrophic phase of their infection strategy. In vitro bioassays using different lipid substrates confirmed the ability of C. truncatum and C. brevisporum isolates from green and red bell peppers to secrete cutinase. The diversity, structure and organization and synteny of the cutinase gene were determined among different Colletotrichum species. Cluster analysis indicated a low level of nucleotide variation among C. truncatum sequences. Nucleotide sequences of C. brevisporum were more related to C. truncatum cutinase nucleotide sequences than to C. gloeosporioides. Cluster patterns coincided with haplotype and there was evidence of significant positive selection with no recombination signatures. The structure of the cutinase gene included two exons with one intervening intron and, therefore, one splice variant. Although amino acid sequences were highly conserved among C. truncatum isolates, diversity “hot spots” were revealed when the 66‐amino acid coding region of 200 fungal species was compared. Twenty cutinase orthologues were detected among different fungal species, whose common ancestor is Pezizomycotina and it is purported that these orthologues arose through a single gene duplication event prior to speciation. The cutinase domain was retained both in structure and arrangement among 34 different Colletotrichum species. The order of aligned genomic blocks between species and the arrangement of flanking protein domains were also conserved and shared for those domains immediately located at the N‐ and C‐terminus of the cutinase domain. Among these were an RNA recognition motif, translation elongation factor, signal peptide, pentatricopeptide repeat, and Hsp70 family of chaperone proteins, all of which support the expression of the cutinase gene. The findings of this study are important to understanding the evolution of the cutinase gene in C. truncatum as a key component of the biotrophic–necrotrophic switch which may be useful in developing gene‐targeting strategies to decrease the pathogenic potential of Colletotrichum species.     

Intraspecific Differentiation of Colletotrichum gloeosporioides sensu lato Based on In Silico Multilocus PCR-RFLP Fingerprinting

Colletotrichum gloeosporioides sensu lato is one of the most common and widely distributed plant pathogens in the world. Understanding fungal biodiversity is hinged on accurate identification and delimitation at the inter- and intraspecific levels. Sequences of the ITS1-5.8S-ITS2 region (ITS), β-tubulin (TUB), actin (ACT), and glyceraldehyde-3-phosphate dehydrogenase (GPDH) genes of 30 C. gloeosporioides sensu lato isolates, collected from anthracnose infected papaya fruits grown in the main production areas in Trinidad, were analyzed by in silico PCR-RFLP analysis with the aim of identifying which gene region(s) had the highest level of intraspecific polymorphism. Restriction site polymorphisms generated from 13 restriction enzymes enabled the identification of specific enzymes that were successful at intraspecific discrimination of the C. gloeosporioides isolates. Genetic distance values were reflective of the level of polymorphisms obtained for the four different gene regions. In both cases (calculated genetic distance and percentage of polymorphic loci from RFLP profiles), ACT and ITS gene regions had the highest level of restriction site polymorphisms and genetic diversity, GPDH and TUB had the lowest. Cluster analysis based on PCR-RFLP genetic distance data revealed sub-specific placement of the isolates which appeared to be gene-dependent. The implications of these findings are discussed relative to biodiversity monitoring and the need for multilocus, polyphasic investigations which must take into account the possibility of exaggerated estimates of genetic diversity.     

Incidence of mycoflora and mycotoxins in some edible fruits and seeds of forest origin

Twelve fungi namelyAlternaria alternata, Aspergillus flavus, A niger, A ochraceus, Actinomucor repens, Capnodoium spp., Curvularia lunata, Fusarium pallidoroseum, F solani, F verticillioides, Penicillium citrinum and Rhizopus stolonifer were recorded from samples ofAegle marmelos, Aesculus indica, Buchanania lanzan andPinus gerardiana. In case ofPrunus amygdalus only Rstolonifer was recorded. A significant variation in pattern of mycoflora incidence was observed in terms of source and season. Fungal infestation in most of the substrates was found to be highest during monsoon. Aflatoxins were the most common mycotoxins elaborated by different isolates ofA flavus obtained fromA marmelos, B lanzan andP gerardiana. The amount of aflatoxins produced by the toxigenic isolates ofA flavus was in the range of traces to 0.9–26.0 μg/ml inA marmelos, 0.8–17.5 μg/ml inP gerardiana and 0.65–13.2 μg/ml inB lanzan. The percentage toxigenicity was comparatively lower in the isolates of other mycotoxigenic fungi. Aflatoxins were detected almost in all the samples analyzed for mycotoxin contamination. However, traces of zearalenone were detected inA marmelos. The concentration of aflatoxin B₁ was in the range of 0.13–0.75 μg/g inA marmelos, 0.09–0.60 μg/g inP gerardiana and 0.01–0.20 ug/g inB lanzan. Mycotoxins were not detected inAesculus indica andPrunus amygdalus.     

An E. coli 5S rRNA Deletion Mutant Useful for the Study of 5S rRNA Structure/Function Relationships

We report on the construction of a novel strain of E. coli that can be useful for studies on the structure/function relationship of 5S rRNAs. The bacterial strain is deficient in six of the eight naturally occurring 5S rRNA genes (operons B, D, H, G, E) and demonstrates a greatly reduced growth rate that can be compensated by the plasmid-encoded expression of 5S rRNA. The relatively large difference in growth rate between compensated and non-compensated mutants provides the basis for a quick and simple assaying system for both the evaluation and mass screening of divergent 5S rRNA sequences for function. We describe the construction of the 5S rRNA deletion mutant BDHGE and characterize the usefulness and limitations of the system for evaluating structure/function relationships of 5S rRNA sequence. Received: 20 August 2000 / Accepted: 2 January 2001     

A <Emphasis Type="Italic">Bacillus thuringiensis</Emphasis> isolation method utilizing a novel stain,low selection and high throughput produced atypical results

Background  

Bacillus thuringiensis is a bacterium known for producing protein crystals with insecticidal properties. These toxins are widely sought after for controlling agricultural pests due to both their specificity and their applicability in transgenic plants. There is great interest in isolating strains with improved or novel toxin characteristics, however isolating B. thuringiensis from the environment is time consuming and yields relatively few isolates of interest. New approaches to B. thuringiensis isolation have been, and continue to be sought. In this report, candidate B. thuringiensis isolates were recovered from environmental samples using a combination of a novel stain, high throughput and reduced selection. Isolates were further characterized by SDS-PAGE, light microscopy, PCR, probe hybridization, and with selected isolates, DNA sequencing, bioassay or Electron Microscopy.     

Effects of dietary flaxseed on vascular contractile function and atherosclerosis during prolonged hypercholesterolemia in rabbits

Dietary flaxseed has significant anti-atherogenic effects. However, the limits of this action and its effects on vascular contractile function are not known. We evaluated the effects of flaxseed supplementation on atherosclerosis and vascular function under prolonged hypercholesterolemic conditions in New Zealand White rabbits assigned to one of four groups for 6, 8, or 16 wk of feeding: regular diet (RG), 10% flaxseed-supplemented diet (FX), 0.5% cholesterol-supplemented diet (CH), and 0.5% cholesterol- and 10% flaxseed-supplemented diet (CF). Cholesterol feeding resulted in elevated plasma cholesterol levels and the development of atherosclerosis. The CF group had significantly less atherosclerotic lesions in the aorta and carotid arteries after 6 and 8 wk than the CH animals. However, the anti-atherogenic effect of flaxseed supplementation was completely attenuated by 16 wk. Maximal tension induced in aortic rings either by KCl or norepinephrine was not impaired by dietary cholesterol until 16 wk. This functional impairment was not prevented by including flaxseed in the high-cholesterol diet. Aortic rings from the cholesterol-fed rabbits exhibited an impaired relaxation response to acetylcholine at all time points examined. Including flaxseed in the high-cholesterol diet completely normalized the relaxation response at 6 and 8 wk and partially restored it at 16 wk. No significant changes in the relaxation response induced by sodium nitroprusside were observed in any of the groups. In summary, dietary flaxseed is a valuable strategy to limit cholesterol-induced atherogenesis as well as abnormalities in endothelial-dependent vasorelaxation. However, these beneficial effects were attenuated during prolonged hypercholesterolemic conditions.