Instituto de Ecología, A.C., Red de Biodiversidad y Sistemática, Carretera Antigua a Coatepec No. 351, El Haya, Xalapa 91070, Veracruz, Mexico.
Fungal Biol. 2013 Sep;117(9):623-37. doi: 10.1016/j.funbio.2013.06.006. Epub 2013 Jun 28.
The nuclear ribosomal DNA of Rhizoctonia species is polymorphic in terms of the nucleotide composition and length. Insertions of 349-410 nucleotides in length with characteristics of group I introns were detected at a single insertion point at the expansion segment D11 of 28S rDNA in 12 out of 64 isolates. Eleven corresponded to Rhizoctonia solani (teleomorph: Thanatephorous) and one (AG-Q) to Rhizoctonia spp. (teleomorph: Ceratobasidium). Sequence data showed that all but AG-Q contained conserved DNA catalytic core regions (P, Q, R, and S) essential for selfsplicing. The predicted secondary structure revealed that base-paired helices corresponded to subgroup IC1. Isolates from same anastomosis group and even subgroups within R. solani were variable with regard to possession of introns. Phylogenetic analyses indicated that introns were vertically transmitted. Unfortunately, sequence data from the conserved region from all 64 isolates were not useful for delimiting species. Analyses with IC1 introns at same insertion point, of both Ascomycota and Basidiomycota indicated the possibility of horizontal transfer at this site. The present study uncovered new questions on evolutionary pattern of change of these introns within Rhizoctonia species.
在核苷酸组成和长度方面，丝核菌属的核核糖体 DNA 是多态的。在 64 个分离株中的 12 个中，在 28S rDNA 的扩展片段 D11 处检测到具有 I 组内含子特征的长度为 349-410 个核苷酸的插入。其中 11 个与立枯丝核菌（同物型：Thanatephorous）相对应，1 个（AG-Q）与丝核菌属（同物型：Ceratobasidium）相对应。序列数据表明，除 AG-Q 外，所有这些都包含自我剪接所必需的保守 DNA 催化核心区域（P、Q、R 和 S）。预测的二级结构显示，碱基配对的螺旋与子组 IC1 相对应。来自相同吻合组的分离株，甚至 R. solani 内的亚组，在是否存在内含子方面存在差异。系统发育分析表明，内含子是垂直传递的。不幸的是，来自所有 64 个分离株的保守区域的序列数据对于种的划分没有用处。对同一插入点的子组 IC1 内含子进行的分析表明，该位点可能存在水平转移。本研究揭示了关于丝核菌属物种中这些内含子进化变化模式的新问题。
