Mitochondrial inheritance in Aspergillus nidulans

SummaryMitochondrial chloramphenicol and oligomycin resistance mutations were used to investigate mitochondrial inheritance in A. nidulans. Mitochondrial RFLPs could not be used to distinguish between paternal and maternal mitochondria because none were detected in the 54 isolates investigated. Several thousand ascospores from each of 111 hybrid cleistothecia from 21 different crosses between 7 heterokaryon incompatible isolates were tested for biparental inheritance. All mitochondrial inheritance was strictly uniparental. Not one instance of paternal inheritance of mitochondria was observed. The implications of our results for the theory that uniparental inheritance evolved to avoid cytoplasmic conflictare discussed. Possible explanations for the maintenance of strict uniparental inheritance of mitochondria in an inbreeding homothallic organism are suggested. The chloramphenicol resistance marker was inherited preferentially to the oligomycin resistance marker probably due to the inhibited energy production of mitochondria with the oligomycin resistance mutation. The maternal parent was determined for 93 hybrid cleistothecia from 17 crosses between 7 different strains. Contraryto previous reports A. nidulans strains functioned as both maternal and paternal parent in most crosses.

Comparing the Resynthesis of Brassica napus L. by Interspecific Somatic and Sexual Hybridization. II. Hybrid Morphology and Identifying Organelle Genomes

Brassica napus (genome aacc), a natural allotetraploid derived from hybridization between B. oleracea L. (genome cc) and B. rapa L. (genome aa), was resynthesized by somatic and sexual hybridization. Seventy-two interspecific somatic (R0) hybrids and 27 sexual (F1) hybrids were produced from the same parent plants. R0 and F1 hybrids displayed morphology that was intermediate to the species parents, but B. rapa characteristics tended to predominate. R0 hybrids with nuclear DNA content equivalent to natural B. napus were uniform for nuclear-encoded traits, whereas allotetraploid F1 hybrids were variable for traits such as morphology, flower color, and seed production. Chloroplast restriction fragment length polymorphisms (RFLPs) showed unequal segregation in the R0 population favoring the chloroplasts of B. rapa; two of the 58 R0 hybrids tested had only the B. oleracea marker and 10 contained markers of both parents. Mitochondrial RFLPs showed a similar bias among the 56 R0 hybrids tested; only four plants showed B. oleracea markers exclusively, and the remaining plants were evenly distributed between having only B. rapa markers or having combinations from both species. In contrast, sexual hybrids displayed only maternal organelle markers.

An Assessment of Genetic Relationships between Members of the Phytophthora megasperma Complex and Phytophthora vignae using Molecular Markers

Genetic relationships between Phytophora megasperma f. sp. glycinea (Pmg) and morphologically similar taxa, P. megasperma f. sp. medicaginis (Pmm), P. megasperma f. sp. trifolii (Pmt), P. megasperma from Douglas Fir (PmDF) and asparagus (PmAS) and Phytophthora vignae, were explored by restriction fragment length polymorphism (RFLP) analysis of nuclear DNA using random genomic multi-copy, cDNA, and ribosomal DNA probes as well as random amplified polymorphic DNA (RAPDs) and RFLP analysis of ribosomal intergenic spacer regions amplified by the polymerase chain reaction (PCR). Each method detected large differences between these taxa and P. megasperma f. sp. glycinea. P. vignae was more closely related to P. megasperma f. sp. glycinea than the other taxa on the basis of the cDNA RFLPs and RFLPs of PCR amplified rDNA intergenic spacer regions. We conclude that each of the taxa examined represent separate species. This supports the most recent reclassification based on mitochondrial RFLPs and electrophoretic protein patterns of the host-specific taxa to P. sojae (Pmg), P. trifolii (Pmt) and P. medicaginis (Pmm).