EXPRESSION OF THE RICE CHLOROPLAST PSAA-PSAB-RPS14 GENE-CLUSTER

The rice plastid genes psaA and psaB encoding the two apoproteins of P700 chlorophyll a protein complex of photosystem I reaction center, and the putative rps14 gene for ribosomal protein S14, are organized into a transcription unit. Northern blot analyses revealed that the polycistronic mRNA is transcribed in leaves of illuminated,and dark-grown rice seedlings. However Western immunoblot analysis detected the accumulation of P700 chlorophyll a protein complex only at 3 h after illuminating the dark-grown seedlings. These observations suggest the expression of psaA and psaB gene products during rice plastid development is light-regulated primarily at translational or post-translational level. S1-nuclease mapping and primer extension located the 5' end of the transcript predominantly at 175 bp upstream of psaA, and the 3' end at 116 bp downstream from rps 14. The transcript is calculated to be 5230 nucleotides long. A heterologous in vitro transcription assay with spinach transcriptionally active high salt extract, followed by S1-nuclease mapping, also located the 5' end of in vitro transcript at around 175 bp upstream of rice psaA.