Maize high chlorophyll fluorescent 60 mutation is caused by an Ac disruption of the gene encoding the chloroplast ribosomal small subunit protein 17

The maize mutation high chlorophyll fluorescence 60-muTable 1 (hcf60-m1), g enerated through Activator (Ac) tagging, has insufficient photosynthetic el ectron transport. Here we show that the Hcf60 gene encodes a protein with s ubstantial amino acid similarity to plant plastid and bacterial ribosomal s mall subunit protein 17 (RPS17) proteins. The lack of detectable HCF60 tran scripts in mutant leaves, and insertion of the transposed Ac element 17 bp upstream of the start of translation in the mutated locus, suggest that lit tle if any RPS17 is produced. The mutant phenotype is consistent with reduc ed plastid translation. Seedling lethal hcf60-m1 plants display temperature and light-dependent chlorophyll deficiencies, a depletion of plastid rRNA pools, and few high-molecular-weight polysomal complexes. Growth under mode rate light conditions (27 degrees C, 100 mu E m(-2) sec(-1)) allows for sub stantial chlorophyll accumulation in mutant leaves, yet the number of funct ional photosystem II complexes appears low. Nevertheless, the presence of a limited but intact C-4 system indicates that some plastid translation occu rs.