Nuclear genes are likely to be responsible, in large part,for the coordination of chloroplast biogenesis and leafdevelopment in higher plants. Nuclear mutations can identifysuch genes even when they do not encode abundant chloroplastproteins, and have been widely used in the analysis ofchloroplast development. However, pleiotropic effects,particularly in the case of pigment deficient mutants, tendto obscure the biochemical lesion responsible for most mutantphenotypes. Transposon mutagenesis and cloning provide analternative approach to the analysis of these mutations. Thesubject of this proposal is the non.photosynthetic maizemutant hcf*106. This mutation has a dramatic effect onthylakoid membrane organisation a key, morphological processduring chloroplast development. Hcf*106 membranes are notdeficient in pigment or lipid biosynthesis, but fail toaccumulate a subset of thylakoid proteins. The mutant genehas been cloned using the transposon Mul as a molecular"tag" and genetic arguments are presented demonstrating theidentity of the clone. The experiments outlined in this proposal are designed todetermine the molecular function of the hcf*106 gene productin thylakoid membrane elaboration, and should provideimportant insights into genetic regulation of chloroplastdevelopment.
