Phloem-Specific Expression of Tyrosine/Dopa Decarboxylase Genes and the Biosynthesis of Isoquinoline Alkaloids in Opium Poppy

Abstract

Tyrosine/dopa decarboxylase (TYDC) catalyzes the formation of tyramine and dopamine and represents the first steps in the biosynthesis of the large and diverse group of tetrahydroisoquinoline alkaloids. Opium poppy accumulates morphine in aerial organs and roots, whereas sanguinarine, which is derived from a distinct branch pathway, accumulates only in roots. Expression of the TYDC gene family in opium poppy was investigated in relation to the organ-specific biosynthesis of these different types of alkaloids. Members of the TYDC gene family are classified into two groups (represented by TYDC1 and TYDC2) and are differentially expressed. In the mature plant, TYDC2-like transcripts are predominant in stems and are also present in roots, whereas TYDC1-like transcripts are abundant only in roots. In situ hybridization analysis revealed that the expression of TYDC genes is developmentally regulated. TYDC 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. Localization of TYDC transcripts in the phloem is consistent with the expected developmental origin of laticifers, which are specialized internal secretory cells that accompany vascular tissues in all organs of select species and that contain the alkaloid-rich latex in aerial organs. The differential expression of TYDC genes and the organ-dependent accumulation of different alkaloids suggest a coordinated regulation of specific alkaloid biosynthetic genes that are ultimately controlled by specific developmental programs.

The roles of latex and the vascular bundle in morphine biosynthesis in the opium poppy, Papaver somniferum

“…Tyrosine͞dopa decarboxylase participates in the very early stages of tetrahydrobenzylisoquinoline alkaloid biosynthesis, acting at the interface between primary and secondary metabolism (6). Tydc transcript has been reportedly detected in phloem in P. somniferum aerial plant parts (31). This finding is consistent with the results reported herein.…”

ALKALOIDBIOSYNTHESIS INPLANTS: Biochemistry, Cell Biology, Molecular Regulation, and Metabolic Engineering Applications

“…The tissue-specific localization of TYDC has been demonstrated in opium poppy (38). TYDC mRNAs are most abundant in the metaphloem of opium poppy stems and roots, and are found only at low levels in developing seed capsules (39). Metaphloem is closely associated with laticifers in opium poppy (37); thus, detection of TYDC mRNAs in metaphloem supports the association of opium poppy BIA biosynthesis with cells ontogenically related to laticifers.…”

“…The root-specific accumulation of sanguinarine in opium poppy (39) suggests that the enzymes involved in its biosynthesis occur only in roots. However, the substantial levels of BBE mRNA (41) and enzyme activity (161) in shoot organs suggest that pathway intermediates involved in sanguinarine biosynthesis are translocated from shoots to roots.…”

Biosíntesis de alcaloides bencilisoquinolínicos

“…En la biosíntesis y almacenamiento de ABI participan diferentes tipos de tejidos, células y orgánulos, por ejemplo en P. somniferum, la biosíntesis de morfina y noscapina ocurre en los tallos y raíces y se acumulan en el citoplasma de células especializadas (células laticíferas) de los carpelos y de las cápsulas de los frutos, mientras que la sanguinarina es biosintetizada y acumulada en las raíces; en B. stolonifera, la berberina al parecer es biosintetizada y almacenada en todos los órganos (23,35,55).…”