Maize contains a Lon protease gene that can partially complement a yeast pim1-deletion mutant

We have identified a gene in maize that encodes a product belonging to the Lon protease family. In yeast and mammals, Lon-type proteases catalyze the ATP-dependent degradation of mitochondrial matrix proteins. The maize gene, which we have designated LON1, is predicted to encode a protein with a molecular mass of 97.7 kDa. Lon1p is more similar in sequence to bacterial Lon proteases than to the yeast and human mitochondrial Lon proteases. LON1 transcripts are present in shoots of 4-day-old etiolated maize seedlings, and transcript levels decrease when these seedlings are heat-shocked. LON1 transcripts are also present at comparable levels in leaves and roots of 2-week-old greenhouse-grown seedlings. In yeast, the mitochondrial Lon-type protease, Pim1p, has been implicated in mitochondrial protein turnover, the assembly of mitochondrial enzyme complexes, and mitochondrial DNA maintenance, and it is essential for respiratory function. We show that maize Lon1p can replace the Pim1p function in yeast for maintaining mitochondrial DNA integrity, but not in the assembly of cytochrome a _ a3 complexes.