Abstract
Quinolizidine alkaloids (QAs) occur mainly in the genus Lupinus. We isolated a lysine/ornithine decarboxylase cDNA (LaDC) and acyltransferase (LaAT) by differential transcript-screening in two Lupinus angustifolius cultivars regarding capability of QA-production. The expression level of LaDC and LaAT were highest in young leaves of the QA-producing cultivar and not detected in the non-producing cultivar. We also obtained LDC cDNAs from two other QA-producing plants, Sophora flavescens and Echinosophora koreensis. Recombinant LDCs from QA-producing plants exhibited decarboxylase activities towards both L-lysine and L-ornithine to the similar extent. Site-directed mutation study of LaDC revealed the important amino acid residues for LDC activity. The overexpression (OX) of LaDC in tobacco hairy roots and BY-2 suspension cells resulted in an enhanced production of cadaverine-derived piperidine alkaloids. The transgenic Arabidopsis plants LaDC-OX accumulated cadaverine, which is never detected in the control plants. These data indicate that these LDCs from QA-producing plants catalyze the decarboxylation of L-lysine to form cadaverine leading to the synthesis of QAs.
