藥用真菌冬蟲夏草多型18S、ITS區域核醣體RNA基因序列之研究

Abstract

冬蟲夏草 (Cordyceps sinensis (Berk.) Sacc.) 自古為我國滋肺補腎的珍貴藥材，由於冬蟲夏草形態觀察鑑定不易，係多利用分子生物技術分析核醣體RNA基因(nuclear ribosomal RNA gene，簡稱nrRNA基因或nrDNA) 18S及內轉錄區ITS1 (internal transcribed spacers 1)、5.8S、ITS2序列作為分類鑑定指標。為解決冬蟲夏草相關nrDNA分類文獻中「複合種」(species complex)、「隱蔽種」(cryptic species) 觀點分歧的現況，本試驗設計多組引子組來擴增供試樣品nrDNA，發現GC、AT-1、AT-2、T等四型nrDNA，且確認每個冬蟲夏草樣品同時具有GC型及另一型nrDNA。本研究結果證明了「單一物種同時具有兩種nrDNA」的現象。此結果可以合理解決兩種觀點的分歧，亦是未來冬蟲夏草分類鑑定上須考量的重要環節，至於各型樣品是否有藥理功能上或地理分佈上的差異，則有待未來進一步研究討論。

Cordyceps sinensis (Berk.) Sacc. is a valued traditional Chinese medicinal fungus. Since it is difficult to identify C. sinensis based on morphological observation, sequences of the 18S and internal transcribed spacer (ITS) regions (ITS1, 5.8S and ITS2) of nuclear ribosomal DNA (nrDNA) have been used to differentiate C. sinensis specimens. In the present study, we designed several primer pairs to amplify the nrDNA of C. sinensis isolates. A novel discovery was that the C. sinensis isolates had four types of nrDNA: GC, AT-1, AT-2 and T. Each isolate contained the GC type and simultaneously contained a further one type. These results provide a novel concept, i.e. the ‘multiple nrDNA type concept’ of C. sinensis classification, which differs from the previous ‘species complex’ and ‘cryptic species’ concept. Accordingly, we propose that the classification of C. sinensis based on nrDNA sequences should take into consideration the composition of nrDNA types. However, the relationship between the medicinal effects and geographical populations with different nrDNA profiles needs further study.