Isolation and characterisation of an evolutionary conserved protein that is involved in photosystem I biogenesis in Arabidopsis thaliana

The recessive Arabidopsis mutant, hcfb12-1 (high chlorophyll fluorescence), was isolated from an ethyl methanesulfonate (EMS) mutagenized Arabidopsis seed pool. Fluorescence measurements, immunoblot and ultrastructure analysis demonstrate that photosystem I (PSI) is the rate limiting electron transport complex in hcfb12-1. The mutant is specifically impaired in the accumulation of psaA/B transcripts, while the transcript levels for the remaining PSI subunits, for subunits of the photosystem II, the cytb6/f-complex and the ribulose-1,5-bisphosphate carboxylase are comparable to the wild type. Hcfb12 was isolated by map-based cloning. The protein is localized in the stroma of the chloroplast and exhibits striking similarities to UMP kinases of prokaryotic origin. In this work the possible role of Hcfb12 in relation to the psaA/psaB/rps14 transcript accumulation is discussed