title: Chloroplast gene suppression of defective ribulosebisphosphate carboxylase/oxygenase in Chlamydomonas reinhardii: evidence for stable heteroplasmic genes.
abstract: The rcl-u-1-18-5B chloroplast mutation results in the absence of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) holoenzyme in the green alga Chlamydomonas reinhardii. The 18-5B mutant strain lacks photosynthesis and displays alight-sensitive, acetate-requiring phenotype. In the present investigations, revertants of 18-5B were recovered that regained photosynthetic competence. These revertants have decreased levels of Rubisco holoenzyme relative to wild type and display heteroplasmicity, segregating wild-type (revertant) and acetate-requiring phenotypes during vegetative growth or through meiosis. One of these revertants, R10-I, was studied further. The heteroplasmicity associated with photoautotrophically-grown R10-I was found to be stable through subcloning and heritable through several crosses. During growth in acetate medium in the dark, where photosynthesis provides no selective advantage, the wild-type phenotype was lost. Acetate-requiring segregants became homoplasmic but wild-type segregants did not. Organellar intergenic-suppression is discussed in light of the observed stable heteroplasmicity.
authors.affiliation: Department of Agronomy, University of Illinois, US Department of Agriculture, Agricultural Research Service, 61801, Urbana, Illinois, USA.
authors.forename: R J
authors.initials: RJ
authors.lastname: Spreitzer
authors.forename: C J
authors.initials: CJ
authors.lastname: Chastain
authors.forename: W L
authors.initials: WL
authors.lastname: Ogren