Volume 10 Part 1 Article 15: Is Sporelessness in Pleurotus ostreatus an Infectious Agent?

Volume 10 Part 1 Article 15
Year 1979
Title: Is Sporelessness in Pleurotus ostreatus an Infectious Agent?
Author: H. Leal-Lara


A dikaryotic strain with sporeless fruit bodies (so called “sporeless strain”) was discovered by chance in Pleurotus ostreatus (Eger, 1970). In Coprinus macrorhizus sporeless mutants have been produced by Takemaru and Kamada (1971). The character “sporelessness” could be transfered by di-mon matings in C. macrorhizus (Takemaru and Kamada, 1971) and in P. ostreatus (EGER etal. 1976). Therefore, both authors assumed that sporelessness in these cases is a gene in the migrating nucleus.

Recently also sporeless strains of C. congregatus have been isolated (Ross et al., 1976, 1977). Virus-like particles were found in monokaryons, which brought about sporeless fruit bodies if they were mated with compatible partners. Sporelessness in C. congregatus was demonstrated to be highly infectious if the monokaryotic stage of the fungus was considered. It could be transmitted from one monokaryon to another, either by pairing of mycelia or by infection with cell free extracts from infected monokaryons. In dikaryons however, these particles seem to be firmly bound to the nucleus, because sporelessness could not be transmitted by extracts from sporeless dikaryons. It could only be transmitted in those pairings where nuclear migration occured (Ross, 1977). These infectious particles behave in some way analogous to prophages integrated in the chromosomes of lysogenic bacteria. A clonal variation to infection was noticed in C. congregatus, which lead to the suggestion that the activity of the infectious agent may be inhibited by host nuclear genes. In P. ostreatus, sporelessness has been found to be expressed with only certain partners, mostly from the same stock (Leal-Lara, unpublished). Considering the experiments with the three sporelessfungi, sporelessness (=sp~) in P. ostreatus may be caused either by expression of a true nuclear gene or an episome.

By a new method, the hypothesis was tested, that sp in P. ostreatus may be integrated in the nuclei in the dikaryon, but free in the cytoplasma in the monokaryotic stage. From the spore bearing parental stock “F” , a sporeless dikaryon was derived by mating two single spore isolates. Both were split into their monokaryotic components (= neohaplonts). Because sp cannot be detected directly, the neohaplonts were paired with a range of compatible monokaryons derived from the original stock “F” and a subculture. The dikaryons obtained from those matings were tested for sporelessness. Various sporeless dikaryons produced from these experiments were also split. Sporelessness was determined among their neohaplonts in matings with tester monokaryons. In all cases sporelessness was detected only in the same type of neohaplonts.

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