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糙皮侧耳（Pleenostreatus（Jacq.）：FR.）库默。通过构建物理图谱和以REC-ADNA为探针的Southern-blot分析，估计了每个亲本mtDNA中产生新的BamHI片段REC-A（7.0kb）的重组位点，并测定了它们的核苷酸序列。亲本mtDNA中的这种重组区域彼此之间具有超过2kb的共有序列，这些共有序列分别被一个和两个具有非共有序列的区域（大小为1.2至1.7kb）分开。而重组mtDNA中REC-A周围区域的核苷酸序列由双亲mtDNA中的共有序列和所有非共有序列组成，表明REC-A周围的多态性是由双亲mtDNA中含有非共有序列的区域整合到另一个mtDNA中引起的。双亲mtDNA的部分共有序列与真菌细胞色素氧化酶亚基1（cx 1）基因的外显子序列同源，而各非共有序列与真菌cx 1基因的I组内含子序列同源。每个内含子具有编码LAGI-DADG基序的ORF，其特征在于参与I组内含子移动性的核酸内切酶。这些结果表明，用于产生REC-A片段的重组机制是通过基因转换阐明的，该基因转换是通过cx 1基因座内内含子的移动性实现的。此外，通过比较亲本和重组体mtDNA的物理图谱，发现亲本mtDNA之间的重组方式在其他重组位点也有相似之处。

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.