Molecular cloning and tissue-specific expression of an anionic peroxidase in zucchini

A calcium-pectate-binding anionic isoperoxidase (APRX) from zucchini (Cucur bita pepo) was purified and subjected to N-terminal amino acid microsequenc ing. The cDNA encoding this enzyme was obtained by reverse transcriptase po lymerase chain reaction from a cDNA library. It encoded a mature protein of 309 amino acids exhibiting all of the sequence characteristics of a plant peroxidase. Despite the presence of a C-terminal propeptide, APRX was found in the apoplast. APRX protein and mRNA were found in the root, hypocotyls, and cotyledons. In situ hybridization showed that the APRX-encoding gene w as expressed in many different tissues. The strongest expression was observ ed in root epidermis and in some cells of the stele, in differentiating tra cheary elements of hypocotyl, in the lower and upper epidermis, in the pali sade parenchyma of cotyledons, and in lateral and adventitious root primord ia. In the hypocotyl hook there was an asymmetric expression, with the inne r part containing more transcripts than the outer part. Treatment with 2,3, 5-triiodobenzoic acid reduced the expression of the APRX-encoding gene in t he lower part of the hypocotyl. Our observations suggest that APRX could be involved in lignin formation and that the transcription of its gene was re lated to auxin level.