MITOCHONDRIAL ELECTRON-TRANSPORT REGULATION OF NUCLEAR GENE-EXPRESSION - STUDIES WITH THE ALTERNATIVE OXIDASE GENE OF TOBACCO

We have isolated a cDNA representing the tobacco (Nicotiana tabacum L. cv Bright Yellow) nuclear gene Aox1, which encodes the alternative ox idase of plant mitochondria. The clone contains the complete coding re gion (1059 base pairs) of a precursor protein of 353 amino acids with a calculated molecular mass of 39.8 kD. A putative transit peptide con tains common signals believed to be important for import and processin g of mitochondrially localized proteins. We have studied changes in Ao x1 gene expression in tobacco in response to changes in cytochrome pat hway activity. inhibition of the cytochrome pathway by antimycin A res ulted in a rapid and dramatic accumulation of Aox1 mRNA, whereas the l evel of mRNAs encoding two proteins of the cytochrome pathway did not change appreciably. This was accompanied by a dramatic increase in alt ernative pathway capacity and engagement in whole cells. Respiration u nder these conditions was unaffected by the uncoupler p-trifluorometho xycarbonylcyanide (FCCP). When inhibition of the cytochrome pathway wa s relieved, levels of Aox1 mRNA returned to control levels, alternativ e pathway capacity and engagement declined, and respiration could once again be stimulated by FCCP. The results show that a mechanism involv ing changes in Aox1 gene expression exists whereby the capacity of the alternative pathway can be adjusted in response to changes in the act ivity of the cytochrome pathway.