| Title | Variations of SSU rDNA Group I Introns in Different Isolates of Cordyceps militaris and the Loss of an Intron during Cross-Mating |
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| Author | Tiantian Lian1,2, Tao Yang1, Junde Sun2, Suping Guo3, Huaijun Yang3, and Caihong Dong1* |
| Address | 1State Key Laboratory of Mycology, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, P. R. China, 2College of Land and Environment, Shenyang Agricultural University, Shenyang 110866, P. R. China, 3Shanxi Research Institute for Medicine and Life Science, Taiyuan, 030006, P. R. China |
| Bibliography | Journal of Microbiology, 52(8),659–666, 2014, |
| DOI | 10.1007/s12275-014-3681-4 |
| Key Words | Cordyceps militaris, group I introns, occurrence, sequence variation, stroma characteristics |
| Abstract | Cordyceps militaris, the type species of genus Cordyceps, is one of the most popular mushrooms and a nutraceutical in eastern Asia. It is considered a model organism for the study of Cordyceps species because it can complete its life cycle when cultured in vitro. In the present study, the occurrence and sequence variation of SSU rDNA group I introns, Cmi.S943 and Cmi.S1199, among different isolates of C. militaris were analyzed. Based on the secondary structure predictions, the Cmi.S943 intron has been placed in subgroup IC1, and the Cmi.S1199 intron has been placed in subgroup IE. No significant similarity between Cmi.S943 and Cmi.S1199 suggested different origins. Three genotypes, based on the frequency and distribution of introns, were described to discriminate the 57 surveyed C. militaris strains. It was found that the genotype was related to the stroma characteristics. The stromata of all of the genotype II strains, which possessed only Cmi.S943, could produce perithecium. In contrast, the stromata of all genotype III strains, which had both Cmi.S943 and Cmi.S1199, could not produce perithecium. Cmi.S1199 showed the lowest level of intra-specific variation among the tested strains. Group I introns can be lost during strain cross-mating. Therefore, we presumed that during cross-mating and recombination, intron loss could be driven by positive Darwinian selection due to the energetic cost of transcribing long introns. |