A 7.5-KBP REGION OF THE MAIZE (T-CYTOPLASM) MITOCHONDRIAL GENOME CONTAINS A CHLOROPLAST LIKE TRNI (CAT) PSEUDO GENE AND MANY SHORT SEGMENTSHOMOLOGOUS TO CHLOROPLAST AND OTHER KNOWN GENES

The DNA sequence of a 7.5-kbp region from the maize cmsT mt genome was determined. Nucleotide-sequence analysis of this region reveals the p resence of a ct-like trnI (CAT) gene, orf31 and orf48 which are respec tively homologous to the trnI (CAT) gene in the maize and rice chlorop last genomes, and to orf28 and orf64 in the rice chloroplast genome. N orthern-blot analysis indicates that the ct-like trnI (CAT) gene is li kely to be a pseudo gene in the maize cmsT mt genome because it is not transcribed. A nucleotide-sequence homology search of this 7.5-kbp re gion reveals several short segments homologous to portions of chloropl ast (ct), mitochondrial (mt) and other known genes. These segments ran ge from 17 bp to 187 bp in length with homology from 71 to 100%. These observations also suggest that the transfer of DNA fragments from the ct genome to the mt genome may have occurred at different times durin g the evolution of the maize mt genome, and that multiple recombinatio n events and rearrangements in both mt and ct genomes have occurred af ter the transfer of DNA fragments from the ct to the mt genome. A few segments were identified by their homology to be portions of genes fro m sources other than the ct genome. While it is known that large fragm ents of ctDNA have been transferred to maize mt genomes, this is the f irst report of the presence of numerous short ctDNA, or other foreign DNA segments, in the maize cmsT mt genome. These segments may provide valuable information regarding the evolution of plant mt genomes.