Localization and Organization of Scopolamine Biosynthesis in Duboisia myoporoides R. Br.

Abstract

Tropane alkaloids (TAs), especially hyoscyamine and scopolamine, are important precursors for anticholinergic and antispasmodic drugs. Hyoscyamine and scopolamine are currently obtained at commercial scale from hybrid crosses of Duboisia myoporoides × Duboisia leichhardtii plants. In this study, we present a global investigation of the localization and organization of TA biosynthesis in a Duboisia myoporoides R. Br. wild-type line. The tissue-specific spatial distribution of TAs within D. myoporoides is presented, including quantification of the TAs littorine, 6-hydroxy hyoscyamine, hyoscyamine, scopolamine and, additionally, hyoscyamine aldehyde as well as scopolamine glucoside. Scopolamine (14.77 ± 5.03 mg g-1), and to a lesser extent hyoscyamine (3.01 ± 1.54 mg g-1) as well as 6-hydroxy hyoscyamine (4.35 ± 1.18 mg g-1), are accumulated in leaves during plant development, with the highest concentration of total TAs detected in 6-month-old plants. Littorine, an early precursor in TA biosynthesis, was present only in the roots (0.46 ± 0.07 mg g-1). During development, the spatial distribution of all investigated alkaloids changed due to secondary growth in the roots. Transcripts of pmt, tr-I and cyp80f1 genes, involved in early stages of TA biosynthesis, were found to be most abundant in the roots. In contrast, the transcript encoding hyoscyamine 6β-hydroxylase (h6h) was highest in the leaves of 3-month-old plants. This investigation presents the spatial distribution of biochemical components as well as gene expression profiles of genetic factors known to participate in TA biosynthesis in D. myoporoides. The results of this investigation may aid in future breeding or genetic enhancement strategies aimed at increasing the yields of TAs in these medicinally valuable plant species.