Oxygen initiation of respiration and mitochondrial biogenesis in rice

Rice growth under aerobic and anaerobic conditions allowed aspects of mitochondrial biogenesis to be identified as dependent on or independent of an oxygen signal. Analysis of transcripts encoding mitochondrial components found that a subset of these genes respond to oxygen (defined as aerobic), whereas others are relatively unaffected by oxygen availability. Mitochondria formed during growth in anaerobic conditions had reduced protein levels of tricarboxylic acid cycle components and cytochrome-containing complexes of the respiratory chain and repressed respiratory functionality. In general, the capacity of the general import pathway was found to be significantly lower in mitochondria isolated from tissue grown under anaerobic conditions, whereas the carrier import pathway capacity was not affected by changes in oxygen availability. Transcript levels of genes encoding components of the protein import apparatus were generally not affected by the absence of oxygen, and their protein abundance was severalfold higher in mitochondria isolated from anaerobically grown tissue. However, both transcript and protein abundances of the subunits of the mitochondrial processing peptidase, which in plants is integrated into the cytochrome bc(1) complex, were repressed under anaerobic conditions. Therefore, in this system, an increase in import capacity is correlated with an increase in the abundance of the cytochrome bc(1) complex, which is ultimately dependent on the presence of oxygen, providing a link between the respiratory chain and protein import apparatus.