Isolation and characterization of the mating-type locus of the barley pathogen Pyrenophora teres and frequencies of mating-type idiomorphs within and among fungal populations collected from barley landraces

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Abstract:

Pyrenophora teres f. sp. teres mating-type genes (MAT-1: 1190 bp; MAT-2: 1055 bp) have been identified. Their predicted proteins, measuring 379 and 333 amino acids, respectively, are similar to those of other Pleosporales, such as Pleospora sp., Cochliobolus sp., Alternaria alternata, Leptosphaeria maculans, and Phaeosphaeria nodorum. The structure of the MAT locus is discussed in comparison with those of other fungi. A mating-type PCR assay has also been developed; with this assay we have analyzed 150 isolates that were collected from 6 Sardinian barley landrace populations. Of these, 68 were P. teres f. sp. teres (net form; NF) and 82 were P. teres f. sp. maculata (spot form; SF). Within each mating type, the NF and SF amplification products were of the same length and were highly similar in sequence. The 2 mating types were present in both the NF and the SF populations at the field level, indicating that they have all maintained the potential for sexual reproduction. Despite the 2 forms being sympatric in 5 fields, no intermediate isolates were detected with amplified fragment length polymorphism (AFLP) analysis. These results suggest that the 2 forms are genetically isolated under the field conditions. In all of the samples of P. teres, the ratio of the 2 mating types was consistently in accord with the 1:1 null hypothesis. This ratio is expected when segregation distortion and clonal selection among mating types are absent or asexual reproduction is rare. Overall, sexual reproduction appears to be the major process that equalizes the frequencies of the 2 mating types within populations.Key words: Pyrenophora teres, mating-types, AFLPs, sexual reproduction, selection, barley.

Les gènes déterminant le type sexuel (MAT-1 : 1190 pb ; MAT-2 : 1055 pb) chez le Pyrenophora teres f. sp. teres ont été identifiés. Les protéines MAT prédites, de 379 et de 333 acides aminés respectivement, sont semblables à celles des autres pléosporales telles que Pleospora sp., Cochliobolus sp., Alternaria alternata, Leptosphaeria maculans et Phaeosphaeria nodorum. La structure du locus MAT est comparée à celle chez d'autres champignons. Un test PCR pour le type sexuel a aussi été mis au point permettant d'analyser 150 isolats provenant de 6 populations de variétés de pays d'orge de la Sardaigne. De ce nombre, 68 était du P. teres f. sp. teres (forme réticulée, NF) et 82 du P. teres f. sp. maculata (forme maculée, SF). Au sein de chaque type sexuel, les amplicons NF et SF étaient de même taille et très semblables quant à leur séquence. Les 2 types sexuels étaient présents au sein des populations NF et SF à l'échelle du champ, ce qui signifie qu'elles ont maintenu leur capacité à se reproduire sexuellement. Malgré la sympatrie des 2 formes au sein de 5 champs, aucun isolat intermédiaire n'a été observé suite à une analyse AFLP (polymorphisme de longueur des fragments amplifiés). Ces résultats suggèrent que les 2 formes sont isolées génétiquement au champ. Chez tous les échantillons du P. teres, le ratio des 2 types sexuels était constamment conforme à l'hypothèse nulle (1:1). Ce ratio est attendu lorsqu'il n'y a pas de distorsion de la ségrégation ou de sélection clonale ou encore lorsque la reproduction asexuée est rare. Globalement, la reproduction sexuée semble le processus principal égalisant la fréquence des 2 types sexuels au sein de ces populations.Mots clés : Pyrenophora teres, types sexuels, AFLP, reproduction sexuée, sélection, orge.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: October 1, 2005

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  • From its inception in 1957, this international cytogenetics journal has catered to the research areas of the members of the Genetics Society of Canada; traditionally, these have included agriculture, entomology, genetics/cytogenetics, and evolutionary mechanisms. The contents of the journal have evolved as contributors developed new technologies and interests. A 20-member Editorial Board is composed of scientists from around the world. Reviews and commentary from respected experts are often featured.
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