Genetics of Chlamydomonas reinhardtii diploids. II. The effects of diploidy and aneuploidy on the transmission of non-Mendelian markers

Characterization of the structure and DNA complexity of mung bean mitochondrial nucleoids

Electron microscopic images of mitochondrial nucleoids isolated from mung bean seedlings revealed a relatively homogeneous population of particles, each consisting of a chromatin-like structure associated with a membrane component. Association of F-actin with mitochondrial nucleoids was also observed. The mitochondrial nucleoid structure identified in situ showed heterogeneous genomic organization. After pulsed-field gel electrophoresis (PFGE), a large proportion of the mitochondrial nucleoid DNA remained in the well, whereas the rest migrated as a 50-200 kb smear zone. This PFGE migration pattern was not affected by high salt, topoisomerase I or latrunculin B treatments; however, the mobility of a fraction of the fast-moving DNA decreased conspicuously following an in-gel ethidium-enhanced UV-irradiation treatment, suggesting that molecules with intricately compact structures were present in the 50-200 kb region. Approximately 70% of the mitochondrial nucleoid DNA molecules examined via electron microscopy were open circles, supercoils, complex forms, and linear molecules with interspersed sigma-shaped structures and/or loops. Increased sensitivity of mtDNA to DNase I was found after mitochondrial nucleoids were pretreated with high salt. This result indicates that some loosely bound or peripheral DNA binding proteins protected the mtDNA from DNase I degradation.

Genetic analysis of mating locus linked mutations in Chlamydomonas reinhardii

The mating-type (mt) locus of Chlamydomonas reinhardii has been analyzed using four mutant strains (imp-1, imp-10, imp-11 and imp-12). All have been shown, or are shown here, to carry mutations linked to either the plus (mt+) or the minus (mt-) locus, and their behavior in complementation tests has allowed us to define several distinct functions for each locus. Specifically, we propose that the mt+ locus contains the following genes or regulatory elements: a locus designated sfu, which is necessary for sexual fusion between gametes; a locus designated upp (uniparental plus), which controls aspects of chloroplast gene inheritance and perhaps also zygote maturation; and a locus designated sad, which functions in sexual adhesion. The mt- locus also contains a sad locus as well as a gene or regulatory element designated mid, which is necessary for the minus dominance in mt+/mt- diploids.

Transmission and recombination of chloroplast genes in asexual crosses of Chlamydomonas reinhardtii. II. Comparisons with observations of sexual diploids

Patterns of biparental chloroplast gene transmission in Chlamydomonas reinhardtii diploids produced by polyethylene glycol (PEG) fusion were found to be similar to those seen in sexual diploids (VanWinkle-Swift and Birky 1978). Examination of the phenotypes of diploid clones showed that the PEG diploids produced a heterogeneous set of allelic frequencies. Neither the frequencies of parental nor recombinant phenotypes were normally distributed. In addition, frequencies of reciprocal recombinant phenotypes showed no significant correlation in the clones from individual PEG diploids. The frequencies of parental phenotypes, on the other hand, were significantly negatively correlated. Like the data from sexual diploids, this is evidence that recombinant frequencies from clones of PEG diploids are not directly related to frequencies of reciprocal recombination. The similarity of results obtained in sexual and PEG diploids supports the hypothesis that the mechanisms operating during biparental chloroplast gene inheritance in PEG diploids are identical to those in sexual diploids.