title: Variegation mutants and mechanisms of chloroplast biogenesis.
abstract: Variegated plants typically have green- and white-sectored leaves. Cells in the green sectors contain normal-appearing chloroplasts, whereas cells in the white sectors lack pigments and appear to be blocked at various stages of chloroplast biogenesis. Variegations can be caused by mutations in nuclear, chloroplast or mitochondrial genes. In some plants, the green and white sectors have different genotypes, but in others they have the same (mutant) genotype. One advantage of variegations is that they provide a means of studying genes for proteins that are important for chloroplast development, but for which mutant analysis is difficult, either because mutations in a gene of interest are lethal or because they do not show a readily distinguishable phenotype. This paper focuses on Arabidopsis variegations, for which the most information is available at the molecular level. Perhaps the most interesting of these are variegations caused by defective nuclear gene products in which the cells of the mutant have a uniform genotype. Two questions are of paramount interest: (1) What is the gene product and how does it function in chloroplast biogenesis? (2) What is the mechanism of variegation and why do green sectors arise in plants with a uniform (mutant) genotype? Two paradigms of variegation mechanism are described: immutans (im) and variegated2 (var2). Both mechanisms emphasize compensating activities and the notion of plastid autonomy, but redundant gene products are proposed to play a role in var2, but not in im. It is hypothesized that threshold levels of certain activities are necessary for normal chloroplast development.
authors.affiliation: Department of Genetics, Development and Cell Biology, Iowa State University, Ames, IA 50011.
authors.forename: Fei
authors.initials: F
authors.lastname: Yu
authors.affiliation: Department of Genetics, Development and Cell Biology, Iowa State University, Ames, IA 50011.
authors.forename: Aigen
authors.initials: A
authors.lastname: Fu
authors.affiliation: Department of Genetics, Development and Cell Biology, Iowa State University, Ames, IA 50011.
authors.forename: Maneesha
authors.initials: M
authors.lastname: Aluru
authors.affiliation: Department of Genetics, Development and Cell Biology, Iowa State University, Ames, IA 50011.
authors.forename: Sungsoon
authors.initials: S
authors.lastname: Park
authors.affiliation: Department of Genetics, Development and Cell Biology, Iowa State University, Ames, IA 50011.
authors.forename: Yang
authors.initials: Y
authors.lastname: Xu
authors.affiliation: Department of Genetics, Development and Cell Biology, Iowa State University, Ames, IA 50011.
authors.forename: Huiying
authors.initials: H
authors.lastname: Liu
authors.affiliation: Department of Genetics, Development and Cell Biology, Iowa State University, Ames, IA 50011.
authors.forename: Xiayan
authors.initials: X
authors.lastname: Liu
authors.affiliation: Department of Genetics, Development and Cell Biology, Iowa State University, Ames, IA 50011.
authors.forename: Andrew
authors.initials: A
authors.lastname: Foudree
authors.affiliation: Department of Genetics, Development and Cell Biology, Iowa State University, Ames, IA 50011.
authors.forename: Milly
authors.initials: M
authors.lastname: Nambogga
authors.affiliation: Department of Genetics, Development and Cell Biology, Iowa State University, Ames, IA 50011.
authors.forename: Steven
authors.initials: S
authors.lastname: Rodermel
mesh_terms: D017360:Arabidopsis / Q000235:genetics*; D002736:Chloroplasts / Q000378:metabolism*; D017343:Genes, Plant; D009154:Mutation