Uniparental inheritance of chloroplast DNA is strict in the isogamous volvocalean Gonium.

Abstract

A problem has remained unresolved regarding the exceptions to the unilateral inheritance of chloroplast DNA (cpDNA) from MT+/female in Chlamydomonas and other volvocaleans demonstrated by the previous genetic analyses. For identification of the parental types of cpDNA, these studies used parents that have differences in restriction fragment length polymorphisms and exhibit partial sexual incompatibility. In the present study, we used sexually compatible parents of the isogamous colonial volvocalean Gonium maiaprilis that seemed an ideal species to identify the pattern of cpDNA inheritance based on the length difference in the putative group I intron interrupted in the Rubisco large subunit gene and objective identification of mating types by the presence or absence of the minus-dominance (MID) gene. We examined patterns of inheritance of cpDNA and presence/absence of a MID ortholog (GmMID) in 107 F(1) progeny of G. maiaprilis that were obtained by inducing germination of separated single zygotes. The results demonstrated no exception of the uniparental inheritance of cpDNA from the MT+ parent (lacking GmMID) in sexually compatible or genetically less divergent strains of G. maiaprilis. The present data suggest that the uniparental inheritance of cpDNA is likely more strict in crossings of less diverged strains or sexually compatible parental volvocaleans, and some genetic inconsistency between the parents may cause exceptional uniparental inheritance of cpDNA.