Plastome Phylogenomics of Aucuba (Garryaceae).

Yuan Huang,Xiong Chen,Linyuan Fan,Jian Huang,Guohua Zhou,Jiahui Chen

doi:10.3389/fgene.2022.753719

Abstract

Aucuba (Garryaceae), which includes approximately ten evergreen woody species, is a genus endemic to East Asia. Their striking morphological features give Aucuba species remarkable ornamental value. Owing to high levels of morphological divergence and plasticity, species definitions of Aucuba remain perplexing and problematic. Here, we sequenced and characterized the complete plastid genomes (plastomes) of three Aucuba species: Aucuba chlorascens, Aucuba eriobotryifolia, and Aucuba japonica. Incorporating Aucuba plastomes available in GenBank, a total of seven Aucuba plastomes, representing six out of ten species of Aucuba, were used for comparative plastome analysis, phylogenetic analysis and divergence time estimation in this study. Comparative analyses revealed that plastomes of Aucuba are highly conserved in size, structure, gene content, and organization, and exhibit high levels of sequence similarity. Phylogenetic reconstruction based on 68 plastid protein-coding genes strongly supported the monophyly of Garryales, Garryaceae and Aucuba. Aucuba eriobotryifolia was sister to the other Aucuba species examined, consistent with its unique fused anther locule. The divergence time of Aucuba was estimated to be approximately late Miocene. Extant Aucuba species derived from recent divergence events associated with the establishment of monsoonal climates in East Asia and climatic fluctuations.

Highlights

Aucuba Thunberg is a small genus of 10 evergreen woody species endemic to East Asia distributed in the Eastern Himalayas, China, Korea, Japan, Myanmar, and Vietnam (Xiang and Boufford, 2005)
De novo assembly yielded three complete Aucuba plastomes, each identically encoding 114 unique genes: 80 protein-coding genes, 30 Transfer RNA genes (tRNA), and 4 rDNA, which is the same as the other four Aucuba plastomes downloaded from GenBank (Table 1)
We found that the length, structure, gene content, and organization of Aucuba plastomes are highly conserved, and exhibit high levels of sequence similarity (Figure 1, Supplementary Figure S2, Table 1)

Summary

Introduction

Aucuba Thunberg is a small genus of 10 evergreen woody species endemic to East Asia distributed in the Eastern Himalayas, China, Korea, Japan, Myanmar, and Vietnam (Xiang and Boufford, 2005). The morphologies of Aucuba species are highly divergent and plastic, making morphology-based taxonomy perplexing and problematic (Xiang and Boufford, 2005) and hindering the effective conservation and exploitation of the germplasm. The taxonomic affinities of Aucuba have been in dispute since the establishment of the genus. This genus was placed into either Cornaceae (Harms, 1898; Wangerin, 1910; Hutchinson, 1967; Cronquist, 1988) or the monotypic family Aucubaceae (Willis and Shaw, 1973; Takhtajan, 1980; Bremer et al, 1998). Since Aucuba and Garrya show high levels of Plastome Phylogenomics of Aucuba

Methods

Results

Conclusion