A MATING TYPE-LINKED MUTATION THAT DISRUPTS THE UNIPARENTAL INHERITANCE OF CHLOROPLAST DNA ALSO DISRUPTS CELL-SIZE CONTROL IN CHLAMYDOMONAS

An intriguing feature of early zygote development in Chlamydomonas rei nhardtii is the active elimination of chloroplast DNA from the mating- type minus parent due presumably to the action of a zygote-specific nu clease. Meiotic progeny thus inherit chloroplast DNA almost exclusivel y from the mating-type plus parent. The plus-linked nuclear mutation m at3 prevents this selective destruction of minus chloroplast DNA and g enerates progeny that display a biparental inheritance pattern. Here w e show that the mat3 mutation creates additional phenotypes not previo usly described: the cells are much smaller than wild type and they pos sess substantially reduced amounts of both mitochondrial and chloropla st DNA. We propose that the primary defect of the mat3 mutation is a d isruption of cell-size control and that the inhibition of the uniparen tal transmission of chloroplast genomes is a secondary consequence of the reduced amount of chloroplast DNA in the mat3 parent.