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), generated through Activator (Ac) tagging, has insufficient photosynthetic electron transport. Here we show that the Hcf60 gene encodes a protein with substantial amino acid similarity to plant plastid and bacterial ribosomal small subunit protein 17 (RPS17) proteins. The lack of detectable HCF60 transcripts in mutant leaves, and insertion of the transposed Ac element 17 bp upstream of the start of translation in the mutated locus, suggest that little if any RPS17 is produced. The mutant phenotype is consistent with reduced 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 moderate light conditions (27 degrees C, 100 mu E m(-2) sec(-1)) allows for substantial chlorophyll accumulation in mutant leaves, yet the number of functional photosystem II complexes appears low. Nevertheless, the presence of a limited but intact C-4 system indicates that some plastid translation occurs.