Abstract
Strain degeneration has been defined as a decrease or loss in the yield of important commercial traits resulting from subsequent culture, which ultimately leads to Reactive Oxygen Species (ROS) production. Pleurotus ostreatus is a lignin-producing nematophagous edible mushroom. Mycelia for mushroom production are usually maintained in subsequent culture in solid media and frequently show symptoms of strain degeneration. The dikaryotic strain P. ostreatus (DkN001) has been used in our lab as a model organism for different purposes. Hence, different tools have been developed to uncover genetic and molecular aspects of this fungus. In this work, strain degeneration was studied in a full-sib monokaryotic progeny of the DkN001 strain with fast (F) and slow (S) growth rates by using different experimental approaches (light microscopy, malondialdehyde levels, whole-genome transcriptome analysis, and chitosan effect on monokaryotic mycelia). The results obtained showed that: (i) strain degeneration in P. ostreatus is linked to oxidative stress, (ii) the oxidative stress response in monokaryons is genotype dependent, (iii) stress and detoxifying genes are highly expressed in S monokaryons with symptoms of strain degeneration, (iv) chitosan addition to F and S monokaryons uncovered the constitutive expression of both oxidative stress and cellular detoxifying genes in S monokaryon strains which suggest their adaptation to oxidative stress, and (v) the overexpression of the cell wall genes, Uap1 and Cda1, in S monokaryons with strain degeneration phenotype indicates cell wall reshaping and the activation of High Osmolarity Glycerol (HOG) and Cell Wall Integrity (CWI) pathways. These results could constitute a hallmark for mushroom producers to distinguish strain degeneration in commercial mushrooms.
Highlights
Filamentous fungi frequently degenerate during their maintenance in culture by showing loss of the ability to reproduce sexually or asexually [1]
Cda1, both involved in cell wall reshaping in slowgrowing monokaryons, moved us to study the effect of chitosan, a biocidal compound with important medicine and agriculture properties [56], which drastically reduced the growth rate in these monokaryons
We studied the growth rates on malt extract solid medium (MESM) of a progeny of 60 monokaryons obtained in 2016 from the dikaryotic strain P. ostreatus DkN001
Summary
Filamentous fungi frequently degenerate during their maintenance in culture by showing loss of the ability to reproduce sexually or asexually [1]. A whole-genome transcriptome analysis profile revealed 11,820 genes and a substantial population of transposable elements The sequence of both protoclones made possible the identification of Single Nucleotide Polymorphisms SNPs [55], which permitted identifying the parental origin allele in monokaryons derived by meiosis from dkN001. This information enabled us to pose questions and design experiments to uncover the underlying genomic differences between fast- and slow-growing monokaryon strains, which showed strain degeneration. Cda (a chitin deacetylase, EC 3.5.1.41), both involved in cell wall reshaping in slowgrowing monokaryons, moved us to study the effect of chitosan, a biocidal compound with important medicine and agriculture properties [56], which drastically reduced the growth rate in these monokaryons
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