A CHLOROPLAST-DERIVED SEQUENCE IS UTILIZED AS A SOURCE OF PROMOTES SEQUENCES FOR THE GENE FOR SUBUNIT-9 OF NADH DEHYDROGENASE (NAD9) IN RICE MITOCHONDRIA

The chloroplast-derived sequence trnS-rps4/3'trnL-trnF-ndhJ-ndhK (4066 bases in length) is present in a region that starts 355 bases upstrea m of the gene for subunit 9 of NADH dehydrogenase (nad9) in the mitoch ondrial genome of rice. Northern blot hybridization revealed that thre e large transcripts of 3.05, 1.62 and 1.05 kb hybridized to strand-spe cific probes for both the nad9 gene and the chloroplast-derived sequen ce, indicating that the nad9 gene was transcribed together with the ch loroplast-derived sequence. From the results of in vitro capping and r ibonuclease protection experiments, as well as primer extension analys is, we identified at least seven sites for the initiation of transcrip tion of nad9 in the chloroplast-derived sequence. All of the initiatio n sites for transcription of the nad9 gene were located in sequences h omologous to chloroplast DNA. Two of seven initiation sites were flank ed by a sequence homologous to the consensus promoter motif that inclu des the CRTA motif (where R is A or G) of the rice mitochondrion. Howe ver, the sequences surrounding the other five sites showed only limite d similarity to the conserved sequence. It is suggested that all the p romoters of the rice nad9 gene exist in a sequence that was transferre d from the chloroplast during evolution, Thus, the chloroplast-derived sequence has a novel, significant function in the mitochondrial genom e of this higher plant.