XVI International Botanical Congess

Female reproductive tissues and wounded leaves from the ornamental tobacco, Nicotiana alata, amass high levels of a series of proteinase inhibitors (PIs) that probably function in protection against insect pests and pathogens. These PIs are produced from a precursor protein (Na-PI) composed of six repeats each with an inhibitory site for trypsin or chymotrypsin. Proteolytic processing of Na-PI within the secretory pathway leads to the production of five single chain PIs of 6kDa together with a two chain inhibitor formed by disulfide-bond linkage between N- and C-terminal peptide fragments. Surprisingly, PI precursors adopt this circular structure regardless of the number of inhibitor domains, suggesting this bracelet-like conformation is characteristic of the widespread potato inhibitor II (PotII) protein family. We will describe events within the secretory pathway that contribute to the circularisation, vacuolar targeting and proteolytic processing of this remarkable precursor molecule as well as potential applications of the protein in insect control.