The salicylic acid-inducible alternative oxidase gene aox1 and genes encoding pathogenesis-related proteins share regions of sequence similarity in their promoters.

We have isolated and characterized a genomic clone, lambda AOSG11, corresponding to aox1, which encodes the 42 kDa alternative oxidase precursor protein of Sauromatum guttatum Schott. The sequence of lambda AOSG11 revealed that aox1 consists of four exons separated by three short introns. Exon three contains the region of aox1 that (1) is highly conserved in the corresponding genes of potato, rice, and yeast, and (2) encodes a region of the deduced protein that is predicted to form two transmembrane alpha-helices. Southern blot analysis of restriction endonuclease-digested genomic DNA, indicated that aox1 is a single, nuclear-encoded gene in S. guttatum. We have determined the transcriptional start site of aox1 using nuclease protection and primer extension experiments. Comparison of the putative promoter region of aox1 to promoters of PR1a and GRP8 revealed some sequence similarity.