CLA1, A NOVEL GENE REQUIRED FOR CHLOROPLAST DEVELOPMENT, IS HIGHLY CONSERVED IN EVOLUTION

An albino mutant designated cla1-1 (for 'cloroplastos glterados', or ' altered chloroplasts') has been isolated from a T-DNA-generated librar y of Arabidopsis thaliana. In cla1-1 plants, chloroplast development i s arrested at an early stage. cla1-1 plants behave like wild-type in t heir capacity to etiolate and produce anthocyanins indicating that the light signal transduction pathway seems to be unaffected. Genetic and molecular analyses show that the disruption of a single gene, CLA1, b y the T-DNA insertion is responsible for the mutant phenotype. RNA exp ression patterns indicate that CLA1 is positively regulated by light a nd that it has different effects on the steady-state RNA levels of som e nuclear- and chloroplast-encoded photosynthetic genes. Although the specific function of the CLA1 gene is still unknown, it encodes a nove l protein conserved in evolution between photosynthetic bacteria and p lants which is essential for chloroplast development in Arabidopsis.