Karyotyping of Neurospora crassa using synaptonemal complex spreads of translocation quadrivalents.

The purposes of the present research are (i) to establish the karyotype of Neursopora crassa using visualization of kinetochores in the synaptonemal complex (SC) spreads, (ii) to assign each chromosome to a linkage group, and (iii) to examine chromosome pairing and recombination nodules in quadrivalents. Two strains containing reciprocal translocations were used: T(I;II)4637, which involves linkage groups I and II, and alcoy, which contains 3 independent translocations involving I and II, IV and V, and III and VI. Visualization of kinetochores in the spreads requires the use of freshly prepared fixatives. Kinetochore locations and arm ratios were documented in all 7 N. crassa chromosomes. This new information, based on kinetochore position, arm ratios, chromosome length, and quadrivalent analyses, enabled unequivocal confirmation of chromosome assignments to genetic linkage groups. Chromosome pairing in a translocation quadrivalent starts at the 4 terminal regions, and proceeds right up to the translocation break point. Recombination nodules are found in all 4 arms of quadrivalents. The ability to identify a specific chromosome to a genetic linkage group together with the ability to visualize recombination nodules and their locations will allow future cytological analysis of recombination events.

A systematic nomenclature of chromosomal elements for hemiascomycete yeasts.

We present a compact, stable, unambiguous and extensible nomenclature for unique chromosomal elements from genomic DNA, developed to meet the increasing need created by the increasing number of yeast sequencing projects. Our proposal, adopted for use in the Génolevures project, is specifically designed to facilitate basic tasks in comparative genomics.

Genetic diversity and vegetative compatibility among Trichoderma harzianum isolates.

Trichoderma harzianum is the collective name of a set of asexual fungal strains which exhibit heterogeneity in genome structure, DNA sequence and behavior. Contour-clamped homogeneous field (CHEF) electrophoresis of the chromosomes of ten isolates of T. harzianum revealed six clearly distinct electrophoretic karyotypes. Of the ten isolates analyzed, four (GH12, G109, Y and YF) could be classified in a single group with identical karyotypes, while the strains T35 and 315 formed a second group. The genome size characteristic of the different isolates fell into a broad range varying from 29.6 to 56.1 Mb. Gene assignments to the resolved chromosomes showed that all genes analyzed were localized on equivalent chromosomes in the isolates belonging to the same group. Analysis of randomly amplified polymorphic DNAs from the ten isolates confirmed the classification into groups and allowed us to distinguish between isolates T35 and 315, as well as between isolates GH12, G109, Y and YF. Direct confrontation assays using isolates of the same group showed compatible interactions, whereas the same experiment carried out with isolates of different groups showed an incompatible interaction characterized by an area of cell damage. Microscopic observation of the compatible interactions showed hyphal fusions between the isolates, similar to those described for vegetative compatible groups in other fungi. The molecular karyotypes correlated well with the compatibility of the isolates. In addition, we have evaluated both electrophoretic karyotype and randomly amplified polymorphic DNAs analysis as criteria for grouping isolates within the genus according to their capacity for biocontrol of plant pathogens.

Electrophoretic karyotypes of isolates of Candida albicans from hospitalized patients.

Electrophoretic karyotypes, namely, the patterns of chromosome-sized DNAs that have been separated by pulsed-field gel electrophoresis, have been reported to vary among different strains of Candida albicans, and can be useful for the delineation of strains. A previous study showed that almost all the electrophoretic karyotypes of isolates of C. albicans collected from the vagina of outpatients were distinguishable from one another. A few of the isolates had a common atypical karyotype and these isolates all had the same phenotype. This report describes the electrophoretic karyotype analysis of isolates from various specimens taken from hospitalized patients. Karyotypes were analysed with respect to the origins of the isolates in terms of two parameters: the number of bands resolved on the gel and a code of four numbers which corresponded to the number of bands that could be separated in each of four sets of chromosome sizes. No specific karyotype was correlated with either the nature of the specimen or the hospital ward to which the patient had been admitted. Most isolates gave a pattern similar to that of FC18 and no atypical karyotypes were found.