TRYPTOPHAN DECARBOXYLASE IS ENCODED BY 2 AUTONOMOUSLY REGULATED GENESIN CAMPTOTHECA-ACUMINATA WHICH ARE DIFFERENTIALLY EXPRESSED DURING DEVELOPMENT AND STRESS

Camptothecin (CPT) is a valuable anti-cancer monoterpene alkaloid prod uced by the Chinese tree Camptotheca acuminata. Tryptophan decarboxyla se (TDC) supplies tryptamine for the indole moiety of CPT and its deri vatives, and is considered a key step in monoterpene indole alkaloid b iosynthesis as it links primary and secondary metabolism. This report describes the isolation and characterization of tdc1 and tdc2, two aut onomously regulated TDC genes from Camptotheca. When expressed in Esch erichia coil, the products of each gene could decarboxylate tryptophan , but were inactive against tyrosine, phenylalanine and 3,4-dihydroxyp henylalanine (dopa). tdc1 was developmentally regulated, having its hi ghest expression level in the apex, young stem and bark, tissues which also contain the highest levels of CPT. Expression of tdc1 also incre ased during seedling development and was correlated with alkaloid accu mulation during germination. tdc2 expression was induced in Camptothec a leaf discs and cell suspension cultures treated with fungal elicitor or methyl jasmonate, treatments which did not affect tdc1 expression. Unlike tdc1, tdc2 expression was not detected in any unstressed Campt otheca tissues nor in developing seedlings. These data suggest that td c1 may be part of a developmentally regulated chemical defense system in Camptotheca, while tdc2 serves as part of a defense system induced during pathogen challenge.