The study of the mechanism of Arabidopsis immutans variegation

Abstract

Variegated plants typically have greenand white-sectored leaves. Cells in the green sectors contain normal-appearing chloroplasts whereas cells in the white (or yellow) 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 review 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: What is the gene product, and how does it function in chloroplast biogenesis? 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