Hydroxypyruvate reductase with a carboxy-terminal targeting signal to microbodies is expressed in Arabidopsis.

Five Arabidopsis EST cDNA clones of hydroxypyruvate reductase (HPR), a photorespiratory enzyme in leaf peroxisomes, were sequenced. Deduced amino acid sequences revealed that HPR in Arabidopsis contained the carboxy-terminal targeting signal to microbodies. Nucleotide sequence analysis showed that the cDNA with the longest insert contained an open reading frame of 1,158 bp which encoded a polypeptide with 386 amino acids with a calculated molecular mass of 42,251 Da. A Southern blot analysis suggested that the Arabidopsis HPR gene, like that of the pumpkin HPR gene, exists as a single copy. Two kinds of pumpkin HPR mRNA might be produced from a single gene by alternative splicing, but the structure of the genomic DNA indicated that the Arabidopsis HPR gene did not undergo alternative splicing. We detected a polypeptide with a molecular mass of 42 kDa in green leaves of Arabidopsis using an HPR-specific antibody. Immunoelectron microscopy revealed that Arabidopsis HPR protein was exclusively localized in leaf peroxisomes in green leaves. These results indicate that HPR is expressed in a form with a carboxy-terminal targeting signal to microbodies and is localized in microbodies in Arabidopsis, suggesting that the differences in the gene structure and the regulation of gene expression of HPR are probably due to species-specific differences in plants.