Genome Size, Molecular Phylogeny, and Evolutionary History of the Tribe Aquilarieae (Thymelaeaceae), the Natural Source of Agarwood.

Azman H Farah,Shiou Yih Lee,Zhihui Gao,Tze Leong Yao,Rozi Mohamed,Maria Madon

doi:10.3389/fpls.2018.00712

Abstract

The tribe Aquilarieae of the family Thymelaeaceae consists of two genera, Aquilaria and Gyrinops, with a total of 30 species, distributed from northeast India, through southeast Asia and the south of China, to Papua New Guinea. They are an important botanical resource for fragrant agarwood, a prized product derived from injured or infected stems of these species. The aim of this study was to estimate the genome size of selected Aquilaria species and comprehend the evolutionary history of Aquilarieae speciation through molecular phylogeny. Five non-coding chloroplast DNA regions and a nuclear region were sequenced from 12 Aquilaria and three Gyrinops species. Phylogenetic trees constructed using combined chloroplast DNA sequences revealed relationships of the studied 15 members in Aquilarieae, while nuclear ribosomal DNA internal transcribed spacer (ITS) sequences showed a paraphyletic relationship between Aquilaria species from Indochina and Malesian. We exposed, for the first time, the estimated divergence time for Aquilarieae speciation, which was speculated to happen during the Miocene Epoch. The ancestral split and biogeographic pattern of studied species were discussed. Results showed no large variation in the 2C-values for the five Aquilaria species (1.35–2.23 pg). Further investigation into the genome size may provide additional information regarding ancestral traits and its evolution history.

Highlights

Accommodating about 800 species worldwide, the family Thymelaeaceae was given its name by the French botanist Michel Adanson in 1763 (Adanson, 1763)
As information about the Aquilaria genome size is still lacking, we conducted genome size estimations for selected species commonly used in plantation to provide ground base information for this genus
Aquilaria species have a genome size in the range of 2C = 1.35–2.5 pg, while other species from the same family, namely Daphne alpina, D. blagayana, D. laureola, D. mezereum, Dirca palustris, Gnidia polystachya, Pimelea linifolia, and Thymelaea hirsuta, have genome sizes between 1.69 and 8.17 pg (Hanson et al, 2005; Morgan and Westoby, 2005; Garcia et al, 2010; Siljak-Yakovlev et al, 2010; Fridley and Craddock, 2015)

Summary

Introduction

Accommodating about 800 species worldwide, the family Thymelaeaceae was given its name by the French botanist Michel Adanson in 1763 (Adanson, 1763). Thymelaeaceae is a cosmopolitan family consisting of 45 genera, including two well-known agarwood-producing genera, Aquilaria Lam. and Gyrinops Gaertn., both in the tribe Aquilarieae. There are 21 accepted species in the genus Aquilaria and nine in Genetic Evolution of Tribe Aquilarieae the genus Gyrinops (The Plant List, 2013), of which 13 from Aquilaria (A. baillonii, A. beccariana, A. crassna, A. filaria, A. hirta, A. khasiana, A. malaccensis, A. microcarpa, A. rostrata, A. rugosa, A. sinensis, A. subintegra, and A. yunnanensis.) and five from Gyrinops (G. caudata, G. ledermannii, G. salicifolia, G. versteegii, and G. walla), reportedly produce agarwood (Mulyaningsih and Yamada, 2007; Lee and Mohamed, 2016b). Due to overwhelming illegal harvesting, these species are currently protected and listed as endangered in Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES, 2013)

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