Molecular genetic analysis of the inter-parental recombination between mitochondrial genomes in higher basidiomycetes

本研究旨在阐明高等担子菌平菇Pleurotus ostreatus(Jacq.)有性杂交亲本线粒体DNA(MtDNA)分子间重组的机制。：Fr.)库默。以REC-A DNA为探针，通过构建物理图谱和Southern-Blot分析，确定了产生新的BamHI片段REC-A(7.0kb)的亲本mtDNA上的重组位点，并测定了它们的核苷酸序列。亲本mtDNA中的这些重组区彼此具有超过2kb的共同序列，它们分别被分为具有非一致序列的一个和两个区域(大小为1.2~1.7kb)。而重组mtDNA中REC-A附近的核苷酸序列是由两个亲本mtDNA中识别的一致序列和所有非一致序列组成的，这表明REC-A周围的多态性是由一个亲本mtDNA中包含的非一致序列的区域整合到另一个中所致。亲本mtDNA之间的部分共有序列与真菌细胞色素氧化酶亚单位1(Cx1)基因的外显子序列同源，每个非共有序列与真菌Cx1基因的I类内含子序列同源。每个内含子都具有ORF，编码一个Lagi-DADG基序，这是参与I组内含子运动的内切酶的特征。这些结果表明，重组产生REC-A片段的机制是通过基因转换来实现的，基因转换是通过Cx1基因座内含子的移动实现的。此外，通过比较亲本和重组mtDNA之间的物理图谱，表明亲本mtDNA之间的重组方式在其他重组位点上也发生了类似的重组。

The aim of this study is to elucidate the mechanism for inter-molecular recombination between parental mitochondrial DNAs (mtDNAs) occurring in sexual cross of higher basidiomycete, Pleurotus ostreatus (Jacq. : FR.) Kummer. The recombination sites in each parental mtDNA for generation of new BamHI fragment, REC-A (7.0 kb), were estimated by construction of the physical maps and by Southern-blot analysis using REC-A DNA as a probe, and their nucleotide sequences were determined. Such recombinational regions in parental mtDNAs possessed more than 2 kb of consensus sequences with each other, which were split by one and two regions with nonconsensus sequences (1.2 to 1.7 kb in size), respectively. While, the nucleotide sequences of the region around REC-A in recombinant mtDNA was consist of consensus and all nonconsensus sequences recognized in both parental mtDNAs, suggesting that the polymorphism around the REC-A was caused by integrations of the regions with nonconsensus sequences contained in one parental mtDNA into the other. Part of consensus sequences between parental mtDNAs indicated homology to exonic sequences of the cytochrome oxidase subunit 1 (cx1) genes of fungi, and also each nonconsensus sequences were homologous to the sequences of group I intron located in the cx1 genes of fungi. Each intron possessed ORF which encoded a LAGI-DADG motif, characteristic of the endonucleases involved in group I intron mobility. These results indicate that the mechanism of recombination for generating the REC-A fragment is elucidated by the gene-conversion, achieved by the mobility of the introns within the cx1 gene locus. Furthermore, by comparison of the physical maps among parental and recombinant mtDNAs, it was suggested that the similar manner of recombinations between parental mtDNAs were occurred in other recombination sites.