Molecular cloning and functional characterization of tyrosine decarboxylase genes from galanthamine-producing Narcissus pseudonarcissus 'King Alfred.'.

Tyrosine decarboxylases (TyDCs) are pyridoxal 5'-phosphate-dependent enzymes that catalyze the conversion of l-tyrosine into tyramine, a key entry point for Amaryllidaceae alkaloid biosynthesis. From transcriptome data of Narcissus pseudonarcissus 'King Alfred', two full-length TyDC isoforms, NpTyDC1 and NpTyDC2, were identified. In this study, both genes were cloned, heterologously expressed in Escherichia coli, and purified for functional characterization. Fluorescent protein tagging indicated nucleocytoplasmic localization of both isoforms. Enzymatic assays coupled with HPLC-MS/MS demonstrated that NpTyDC1 exhibits decarboxylase activity with a strong preference for l-tyrosine, producing tyramine as the predominant product. In contrast, NpTYDC2 showed no detectable tyrosine decarboxylase activity under the conditions tested, and no tryptophan decarboxylation despite structural features associated with indole decarboxylases but displayed minor activity toward l-phenylalanine. Collectively, these findings establish NpTyDC1 as a strong candidate for directing tyrosine into the Amaryllidaceae alkaloid biosynthesis. By integrating computational predictions with biochemical validation, this study provides new insight into the TyDC functional diversity in Narcissus.