HYDROXYPYRUVATE REDUCTASE WITH A CARBOXY-TERMINAL TARGETING SIGNAL TOMICROBODIES 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 ca rboxy-terminal targeting signal to microbodies. Nucleotide sequence an alysis showed that the cDNA with the longest insert contained an open reading frame of 1,158 bp which encoded a polypeptide with 386 amino a cids with a calculated molecular mass of 42,251 Da, A Southern blot an alysis suggested that the Arabidopsis HPR gene, like that of the pumpk in HPR gene, exists as a single copy, Two kinds of pumpkin HPR mRNA mi ght be produced from a single gene by alternative splicing, but the st ructure of the genomic DNA indicated that the Arabidopsis HPR gene did not undergo alternative splicing. We detected a polypeptide with a mo lecular mass of 42 kDa in green leaves of Arabidopsis using an HPR-spe cific antibody. Immunoelectron microscopy revealed that Arabidopsis HP R protein was exclusively localized in leaf peroxisomes in green leave s, These results indicate that HPR is expressed in a form with a carbo xy-terminal targeting signal to microbodies and is localized in microb odies in Arabidopsis, suggesting that the differences in the gene stru cture and the regulation of gene expression of HPR are probably due to species-specific differences in plants.