Abstract

Although the evolutionary significance of the early-diverging flowering plant Amborella (Amborella trichopoda Baill.) is widely recognized, its metabolic landscape, particularly specialized metabolites, is currently underexplored. In this work, we analyzed the metabolomes of Amborella tissues using liquid chromatography high-resolution electrospray ionization mass spectrometry (LC-HR-ESI-MS). By matching the mass spectra of Amborella metabolites with those of authentic phytochemical standards in the publicly accessible libraries, 63, 39, and 21 compounds were tentatively identified in leaves, stems, and roots, respectively. Free amino acids, organic acids, simple sugars, cofactors, as well as abundant glycosylated and/or methylated phenolic specialized metabolites were observed in Amborella leaves. Diverse metabolites were also detected in stems and roots, including those that were not identified in leaves. To understand the biosynthesis of specialized metabolites with glycosyl and methyl modifications, families of small molecule UDP-dependent glycosyltransferases (UGTs) and O-methyltransferases (OMTs) were identified in the Amborella genome and the InterPro database based on conserved functional domains. Of the 17 phylogenetic groups of plant UGTs (A–Q) defined to date, Amborella UGTs are absent from groups B, N, and P, but they are highly abundant in group L. Among the 25 Amborella OMTs, 7 cluster with caffeoyl-coenzyme A (CCoA) OMTs involved in lignin and phenolic metabolism, whereas 18 form a clade with plant OMTs that methylate hydroxycinnamic acids, flavonoids, or alkaloids. Overall, this first report of metabolomes and candidate metabolic genes in Amborella provides a starting point to a better understanding of specialized metabolites and biosynthetic enzymes in this basal lineage of flowering plants.

Highlights

  • Amborella (Amborella trichopoda Baill.), a short shrub native to the tropical rainforests of NewCaledonia, is the only living species in the Amborellales, the earliest diverging order of flowering plants [1]

  • 63, 39, and 21 compounds were tentatively identified in leaves, stems, and roots of Amborella, respectively, with peak areas ranging from 5.4 × 106 to 2.7 × 1010 (Tables S1–S3)

  • Processing, 63, 39, and 21 compounds were tentatively identified in leaves, stems, and roots of Amborella, respectively, with peak areas ranging from 5.4 × 106 to 2.7 × 1010 (Tables S1–S3)

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Summary

Introduction

Amborella (Amborella trichopoda Baill.), a short shrub native to the tropical rainforests of NewCaledonia, is the only living species in the Amborellales, the earliest diverging order of flowering plants (angiosperms) [1]. Despite its widely recognized importance in understanding flowering plant phylogeny and land plant evolution, little is known about the metabolomes, in particular specialized metabolites (secondary metabolites), of Amborella. Plant specialized metabolites participate in beneficial and defensive interactions between plants and the environment [3,4,5]. Their bioactivities in humans have been exploited as a source of nutraceuticals (e.g., phytonutrients) and pharmaceuticals (e.g., anticancer agents) [6]. Plant specialized metabolites can be classified into three major groups: terpenoids (isoprenoids), phenolics, and alkaloids

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