A WOUND-INDUCIBLE AND METHYL-JASMONATE-INDUCIBLE TRANSCRIPT CODING FOR A MYROSINASE-ASSOCIATED PROTEIN WITH SIMILARITIES TO AN EARLY NODULIN

Myrosinase is regarded as a defense-related enzyme in the Brassicaceae and is capable of hydrolyzing glucosinolates into various compounds, some of which are toxic. Several myrosinase isoenzymes exist, and some of them have been found in association with nonmyrosinase proteins. O ne of these associated proteins, myrosinase-associated protein (MyAP), was purified from seeds of Brassica napus both in complexes with myro sinase and in a free form. MyAP is a glycosylated, 40-kD protein with at least one intramolecular disulfide bridge. A monoclonal anti-MyAP a ntibody precipitated myrosinase activity from B. napus seed extracts a nd in these complexes both a 65- and a 70-kD myrosinase were present. The subsequent cloning and analysis revealed the existence of a gene f amily encoding MyAP or MyAP-related protein and that transcripts corre sponding to MyAP in nonwounded plants are found predominantly in seeds . At least some members of the gene family exhibited responsiveness to ward wounding and methyl jasmonate vapor. MyAP displayed considerable similarity to an early nodulin (ENOD8) from Medicago sativa and to a p roline-rich protein (APG), described as anther specific, from Arabidop sis thaliana and B. napus. Similarity to expressed sequence tags from both A. thaliana and Oryza sativa has also been found.