Phylogeny Predicts the Quantity of Antimalarial Alkaloids within the Iconic Yellow Cinchona Bark (Rubiaceae: Cinchona calisaya).

Carla Maldonado,Else Holmfred,Nina Rønsted,Claus Cornett,Alexandre Antonelli,Steen H Hansen,Christopher J Barnes,Claes Persson

doi:10.3389/fpls.2017.00391

Abstract

Considerable inter- and intraspecific variation with respect to the quantity and composition of plant natural products exists. The processes that drive this variation remain largely unknown. Understanding which factors determine chemical diversity has the potential to shed light on plant defenses against herbivores and diseases and accelerate drug discovery. For centuries, Cinchona alkaloids were the primary treatment of malaria. Using Cinchona calisaya as a model, we generated genetic profiles of leaf samples from four plastid (trnL-F, matK, rps16, and ndhF) and one nuclear (ITS) DNA regions from twenty-two C. calisaya stands sampled in the Yungas region of Bolivia. Climatic and soil parameters were characterized and bark samples were analyzed for content of the four major alkaloids using HPLC-UV to explore the utility of evolutionary history (phylogeny) in determining variation within species of these compounds under natural conditions. A significant phylogenetic signal was found for the content of two out of four major Cinchona alkaloids (quinine and cinchonidine) and their total content. Climatic parameters, primarily driven by changing altitude, predicted 20.2% of the overall alkaloid variation, and geographical separation accounted for a further 9.7%. A clade of high alkaloid producing trees was identified that spanned a narrow range of altitudes, from 1,100 to 1,350 m. However, climate expressed by altitude was not a significant driver when accounting for phylogeny, suggesting that the chemical diversity is primarily driven by phylogeny. Comparisons of the relative effects of both environmental and genetic variability in determining plant chemical diversity have scarcely been performed at the genotypic level. In this study we demonstrate there is an essential need to do so if the extensive genotypic variation in plant biochemistry is to be fully understood.

Highlights

Bark from Cinchona trees (Cinchona L., Rubiaceae) of the Andean mountain forests produce quinine alkaloids, which were the only effective treatment of malaria for more than four centuries (Honigsbaum, 2001; Kaufman and Ruveda, 2005)
Bark and roots are the main source of Cinchona alkaloids, whereas cinchophyllines are reported from leaves (Aerts et al, 1991)
This work represents one of the first attempts to simultaneously explore the relative effects of genotype and environmental variation in determining plant secondary metabolite production under natural conditions

Summary

Introduction

Bark from Cinchona trees (Cinchona L., Rubiaceae) of the Andean mountain forests produce quinine alkaloids, which were the only effective treatment of malaria for more than four centuries (Honigsbaum, 2001; Kaufman and Ruveda, 2005). C. calisaya is one of 23 species of trees in the genus Cinchona described to date, which produce varying amounts of alkaloids. The four major Cinchona alkaloids (quinine, quinidine, cinchonine, and cinchonidine) (Figure 2a) all possess antimalarial activity but have different pharmacological profiles (Taggart et al, 1948; Hill, 1963; Bruce-Chwatt, 1990). Since the first isolation of quinine in 1820 over 30 minor and less studied Cinchona alkaloids have been described from the genus (Kacprzak, 2013). Cinchona type alkaloids have been found in the related genera Ladenbergia Klotzsch and Remijia DC (Okunade et al, 2001; Ruiz-Mesia et al, 2005; Cosenza et al, 2013)

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