Cell-type-specific expression of genes encoding subunits of plant mitochindrail ATP synthase and their coordiantion

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F_1-ATPase of plant mitochondria is composed of six subunits of alpha, beta, gamma, delta, delta', and epsilon. Subunits other than alpha, that is encoded by mitochondrial genome, are encoded by nuclear genes. We have isolated nuclear genes for sigma' and epsilon subunits from sweet potato(Ipomoea batatas) or closely related wild specied (Ipomoea trifida), and determined their nucleotide sequences. Similar the the sigma subunit, these subunits were encoded by multiple genes in the genome. Nuclear genes for the sigma' subunit contained one intron, and exons of these two genes were almost identical to each other. On the other hand, nucleotide sequences of exons from two genes for the sigma subunit were only 81.6% identical to each other. We constructed fusion genes in which promoter fragments from two nuclear genes for the delta subunits, that had been characterixed proviously, were fused to the GUS coding sequence. These fusion genes showed constitutive expression in all of the organs examined. Histochemical examination of expression of fusion genes revealed tha their expression was most strong in phloem tissues of leaves and stems that contain mitochondria-enriched compoanion cells. Between the two fusion genes, the level of expression in roots differed significantly. Futhermore, expression of the fusion gene during the growth of transformed cells of tobacco in suspension culture was also significantly different between the two promoters. These results suggested that multiple genes for nuclear subunits of F_1 ATPase are regulated differently.