Genetics, Vol 136, 867-877, Copyright © 1994


INVESTIGATIONS

A Suppressor of a Mating-Type Limited Zygotic Lethal Allele Also Suppresses Uniparental Chloroplast Gene Transmission in Chlamydomonas monoica

K. VanWinkle-Swift, R. Hoffman, L. Shi and S. Parker
Department of Biological Sciences, Northern Arizona University, Flagstaff, Arizona 86011

Uniparental inheritance of Chlamydomonas chloroplast genes is thought to involve modification of maternal (mt(+)) chloroplast genomes to protect against a nuclease that is activated after gamete fusion. The mating-type limited mtl-1 mutant strain of Chlamydomonas monoica is unable to protect mt(+)-derived chloroplast DNA. Zygotes homozygous for mtl-1 lose all chloroplast DNA and fail to germinate. We have selected for suppression of this zygote-specific lethality, and have obtained 20 mutant strains that produce viable homozygotes despite the continued presence of the mtl-1 allele. Genetic analysis indicates that the suppressor mutations are all recessive alleles at a single locus (sup-1) which is unlinked to mtl-1. Crosses between sup-1 strains carrying distinctive chloroplast antibiotic resistance markers also show predominantly biparental chloroplast gene transmission. Chloroplast nucleoids of both parental origins (stained with the DNA-specific fluorochrome, DAPI) are retained in the zygotes homozygous for sup-1. The data are compatible with the idea that the sup-1 (suppressor of uniparental inheritance) locus may encode a chloroplast DNA nuclease that is expressed from both parental genomes.


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P. J. Ferris, E. V. Armbrust, and U. W. Goodenough
Genetic Structure of the Mating-Type Locus of Chlamydomonas reinhardtii
Genetics, January 1, 2002; 160(1): 181 - 200.
[Abstract] [Full Text] [PDF]