The active digestion of uniparental chloroplast DNA in a single zygote of Chlamydomonas reinhardtii is revealed by using the optical tweezer

The non-Mendelian inheritance of organelle genes is a phenomenon common to almost all eukaryotes, and in the isogamous alga Chlamydomonas reinhardtii, chloroplast (cp) genes are transmitted from the mating type positive (mt()) parent. In this study, the preferential disappearance of the fluorescent cp nucleoids of the mating type negative (mt(-)) parent was observed in li ving young zygotes, To study the change in cpDNA molecules during the prefe rential disappearance, the cpDNA of mt(+) or mt(-) origin was labeled separ ately with bacterial aadA gene sequences. Then, a single zygote with or wit hout cp nucleoids was isolated under direct observation by using optical tw eezers and investigated by nested PCR analysis of the aadA sequences, This demonstrated that cpDNA molecules are digested completely during the prefer ential disappearance of mt(-) cp nucleoids within 10 min, whereas mt(+) cpD NA and mitochondrial DNA are protected from the digestion. These results in dicate that the non-Mendelian transmission pattern of organelle genes is de termined immediately after zygote formation.