Pj. Facchini et V. Deluca, PHLOEM-SPECIFIC EXPRESSION OF TYROSINE DOPA DECARBOXYLASE GENES AND THE BIOSYNTHESIS OF ISOQUINOLINE ALKALOIDS IN OPIUM POPPY, The Plant cell, 7(11), 1995, pp. 1811-1821
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.