Abstract
The direct evidence of the digestion of paternal mitochondrial DNA (mtDNA) have been found in the true slime mold. This was the first report on the selective digestion of mtDNA inside the zygote, and would be the striking mechanism of maternal inheritance of mitochondria. Moreover, two mitochondrial nuclease activities have been detected in this organism as candidates for the nucleases responsible for selective digestion of mtDNA. In the true slime mold, an additional feature is concerned in the uniparental inheritance of mitochondria. Although mitochondria are believed to be inherited from maternal lineage in nearly all eukaryotes, the mating types of the true slime mold Physarum polycephalum is not restricted to two: there are three mating loci matA, matB, and matC, and these loci have 15, 15, and 3 alleles, respectively. Interestingly, the transmission patterns of mtDNA is determined by the matA locus, in a hierarchical fashion (matA hierarchy) as follows: matA7 > matA2 > matA11 > matA12 > matA15/matA16> matA1 > matA6. The strain possessing higher status of matA would be the mtDNA donor in crosses. Furthermore, we have found that some crosses showed biparental inheritance of mitochondria. This review describes the phenomenon of hierarchical transmission of mtDNA in the true slime mold, and discusses the presumed molecular mechanism of maternal and biparental inheritance.
