Identification of cDNA encoding cytochrome c oxidase subunit 5c (COX5c) from rice: comparison of its expression with nuclear-encoded and mitochondrial-encoded COX genes

Little is presently known about the nuclear-encoded genes for cytochrome c oxidase (COX) in higher plants. In rice, only the nuclear-encoded COX5b gen e has been reported. To understand the relationship between the expression of nuclear-encoded and mitochondrial-encoded COX genes in rice, we first ch aracterized a cDNA encoding one of the other nuclear COX genes, COX5c, whic h encodes 63 amino acids. The deduced amino acid sequence of COX5c from ric e was highly homologous to that from sweet potato. Genomic Southern hybridi zation indicated that the rice COX5c subunit is encoded by a single copy of the COX5c gene. Furthermore, we compared the expression patterns of the nu clear-encoded COX5c and COX5b genes with the expression pattern of the mito chondrial-encoded COX1 gene among several organs by Northern blot analysis. The results suggested that regulatory systems of expression between the nu clear-encoded and the mitochondrial-encoded COX genes are different among d ifferent organs in rice.