Genetic Diversity and Structure of Japanese Endemic Genus Thujopsis (Cupressaceae) Using EST-SSR Markers

Michiko Inanaga,Yoichi Hasegawa,Kentaro Mishima,Katsuhiko Takata

doi:10.3390/f11090935

Michiko Inanaga, Yoichi Hasegawa + Show 2 more

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https://doi.org/10.3390/f11090935

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Abstract

The genus Thujopsis (Cupressaceae) comprises monoecious coniferous trees endemic to Japan. This genus includes two varieties: Thujopsis dolabrata (L.f.) Siebold et Zucc. var. dolabrata (southern variety, Td) and Thujopsis dolabrata (L.f.) Siebold et Zucc. var. hondae Makino (northern variety, Th). The aim of this study is to understand the phylogeographic and genetic population relationships of the genus Thujopsis for the conservation of genetic resources and future breeding. A total of 609 trees from 22 populations were sampled, including six populations from the Td distribution range and 16 populations from the Th distribution range. The genotyping results for 19 expressed sequence tag (EST)-based simple sequence repeat (SSR) markers, followed by a structure analysis, neighbor-joining tree creation, an analysis of molecular variance (AMOVA), and hierarchical F statistics, supported the existence of two genetic clusters related to the distribution regions of the Td and Th varieties. The two variants, Td and Th, could be defined by their provenance, in spite of the ambiguous morphological differences between the varieties. The distribution ranges of both variants, which have been defined from their morphology, was confirmed by genetic analysis. The Th populations exhibited relatively uniform genetic diversity, most likely because Th refugia in the glacial period were scattered throughout their current distribution area. On the other hand, there was a tendency for Td’s genetic diversity to decrease from central to southern Honshu island. Notably, the structure analysis and neighbor-joining tree suggest the hybridization of the two varieties in the contact zone. More detailed studies of the genetic structure of Td are required in future analyses.

Highlights

Conifers are a dominant plant type found in the vast boreal forests of the North American and Eurasian continents
Evidence from expressed sequence tag (EST)-simple sequence repeat (SSR) markers suggested that the two variants of the genus Thujopsis, Thujopsis dolabrata (L.f.) Siebold et Zucc. var. dolabrata (Td) and Thujopsis dolabrata (L.f.) Siebold et Zucc. var. hondae Makino (Th), were clearly distinct, as assessed using structure analysis and a neighbor-joining tree
The two varieties could be defined by their provenance, in spite of the ambiguous morphological differences between them

Summary

Introduction

Conifers are a dominant plant type found in the vast boreal forests of the North American and Eurasian continents. They represent an important forest resource in many countries because of their superior wood properties, including straighter trunks and stronger yet lighter wood compared to those of most angiosperms [1]. Wild populations of trees are an important genetic resource and are required for breeding programs that aid in the selection of new plant varieties suitable for withstanding a range of environmental conditions, diseases, and future climate change [2,3,4]. It is important to examine the genetic diversity and phylogeography of a wide range of wild populations, including in the context of conifer breeding

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