The application of DNA methylation studies to the analysis of chloroplast evolution

Review of cytological studies on cellular and molecular mechanisms of uniparental (maternal or paternal) inheritance of plastid and mitochondrial genomes induced by active digestion of organelle nuclei (nucleoids)

In most sexual organisms, including isogamous, anisogamous and oogamous organisms, uniparental transmission is a striking and universal characteristic of the transmission of organelle (plastid and mitochondrial) genomes (DNA). Using genetic, biochemical and molecular biological techniques, mechanisms of uniparental (maternal and parental) and biparental transmission of organelle genomes have been studied and reviewed. Although to date there has been no cytological review of the transmission of organelle genomes, cytology offers advantages in terms of direct evidence and can enhance global studies of the transmission of organelle genomes. In this review, I focus on the cytological mechanism of uniparental inheritance by "active digestion of male or female organelle nuclei (nucleoids, DNA)" which is universal among isogamous, anisogamous, and oogamous organisms. The global existence of uniparental transmission since the evolution of sexual eukaryotes may imply that the cell nuclear genome continues to inhibit quantitative evolution of organelles by organelle recombination.

Epifluorescent microscopic evidence for maternal inheritance of chloroplast DNA

Maternal inheritance of chloroplast genes occurs in the isogamous green alga Chlamydomonas reinhardii. It has been shown using biochemical techniques that the chloroplast DNA of male origin is preferentially lost by 6 h after mating. DNAs in the chloroplast are organized by proteins into about 10 chloroplast nucleoids. Therefore, if chloroplast DNA in zygotes is preferentially destroyed, the disappearance of chloroplast nucleoids from male gametes should be observable during zygote formation by high resolution epifluorescent microscopy. Here we present the first fluorescent microscopic evidence that in C. reinhardii, about eight chloroplast nucleoids from the male parent disappear during the first 40-50 min after mating, while those from the female parent persist and finally fuse together to form one large chloroplast nucleoid.