PHLOEM-SPECIFIC EXPRESSION OF TYROSINE DOPA DECARBOXYLASE GENES AND THE BIOSYNTHESIS OF ISOQUINOLINE ALKALOIDS IN OPIUM POPPY

Tyrosine/dopa decarboxylase (TYDC) catalyzes the formation of tyramine and dopamine and represents the first steps in the biosynthesis of th e large and diverse group of tetrahydroisoquinoline alkaloids, Opium p oppy accumulates morphine in aerial organs and roots, whereas sanguina rine, which is derived from a distinct branch pathway, accumulates onl y in roots. Expression of the TYDC gene family in opium poppy was inve stigated in relation to the organ-specific biosynthesis of these diffe rent types of alkaloids, Members of the TYDC gene family are classifie d into two groups (represented by TYDC1 and TYDC2) and are differentia lly expressed, in the mature plant, TYDC2-like transcripts are predomi nant in stems and are also present in roots, whereas TYDC1-like transc ripts are abundant only in roots, In situ hybridization analysis revea led that the expression of TYDC genes is developmentally regulated. TY DC transcripts are associated with vascular tissue in mature roots and stems but are also expressed in cortical tissues at earlier stages of development, Expression of TYDC genes is restricted to metaphloem and to protoxylem in the vascular bundles of mature aerial organs, Locali zation of TYDC transcripts in the phloem is consistent with the expect ed developmental origin of laticifers, which are specialized internal secretory cells that accompany vascular tissues in all organs of selec t species and that contain the alkaloid-rich latex in aerial organs. T he differential expression of TYDC genes and the organ-dependent accum ulation of different alkaloids suggest a coordinated regulation of spe cific alkaloid biosynthetic genes that are ultimately controlled by sp ecific developmental programs.