Evidence for two types of nrDNA existing in Chinese medicinal fungus <em>Ophiocordyceps sinensis</em>

Chih-Sheng Chen; Ching-Tsan Huang; Ruey-Shyang Hseu; Chih-Sheng Chen; Ching-Tsan Huang; Ruey-Shyang Hseu

doi:10.3934/genet.2017.3.192

AIMS Genetics

2017, Volume 4, Issue 3: 192-201. doi: 10.3934/genet.2017.3.192

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Research article

Evidence for two types of nrDNA existing in Chinese medicinal fungus Ophiocordyceps sinensis

Institute of Microbiology and Biochemistry, College of Life Science, National Taiwan University, Taipei, Taiwan (R.O.C)

Received: 28 December 2016 Accepted: 05 July 2017 Published: 25 August 2017

Nuclear ribosomal DNA (nrDNA) sequences are widely used in the molecular classification of fungi. Previous phylogenetic studies of highly-valued traditional Chinese medicinal fungus Ophiocordyceps sinensis were mostly based on 18S and internal transcribed spacer (ITS) regions (ITS1, 5.8S and ITS2) of nrDNA. However, the disparity manifest in the low sequences identities between different O. sinensis isolates has led to argumentative hypotheses for this phenomenon, such as the “species complex” or “cryptic species” hypotheses. In the present study, four types of nrDNA (GC, AT-1, AT-2, and T) were identified using four primer pairs to amplify the nrDNA of six O. sinensis isolates. We demonstrate that each O. sinensis isolate contained two types of nrDNA, the omnipresent GC-type and a coexistent type alternating between the remaining three. This crucial discovery challenges the established notion of one type of nrDNA per species. We therefore propose that the composition of nrDNA types should be taken into consideration in studies of fungal genetics and classification.
- Ophiocordyceps sinensis,
- nrDNA,
- species complex,
- cryptic species
Citation: Chih-Sheng Chen, Ching-Tsan Huang, Ruey-Shyang Hseu. Evidence for two types of nrDNA existing in Chinese medicinal fungus Ophiocordyceps sinensis[J]. AIMS Genetics, 2017, 4(3): 192-201. doi: 10.3934/genet.2017.3.192

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Abstract

Nuclear ribosomal DNA (nrDNA) sequences are widely used in the molecular classification of fungi. Previous phylogenetic studies of highly-valued traditional Chinese medicinal fungus Ophiocordyceps sinensis were mostly based on 18S and internal transcribed spacer (ITS) regions (ITS1, 5.8S and ITS2) of nrDNA. However, the disparity manifest in the low sequences identities between different O. sinensis isolates has led to argumentative hypotheses for this phenomenon, such as the “species complex” or “cryptic species” hypotheses. In the present study, four types of nrDNA (GC, AT-1, AT-2, and T) were identified using four primer pairs to amplify the nrDNA of six O. sinensis isolates. We demonstrate that each O. sinensis isolate contained two types of nrDNA, the omnipresent GC-type and a coexistent type alternating between the remaining three. This crucial discovery challenges the established notion of one type of nrDNA per species. We therefore propose that the composition of nrDNA types should be taken into consideration in studies of fungal genetics and classification.

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