Abstract：
Acanthus is a distinctive genus that covers three species with different ecological niches including Acanthus mollis (arid terrestrial), Acanthus leucostachyus (damp forest) and Acanthus ilicifolius (coastal intertidal). It is an intriguing question how these species evolved from terrestrial to coastal intertidal. In the present study, we assembled chloroplast genomes of A. ilicifolius, A. leucostachyus and A. mollis, which exhibited typical quadripartite structures. The sizes were 150,758, 154,686 and 150,339 bp that comprised a large single copy (LSC, 82,963, 86,461 and 82,612 bp), a small single copy (SSC, 17,191, 17,511 and 17,019 bp), and a pair of inverted repeats (IRs, 25,302, 25,357 and 25,354 bp), respectively. Gene annotation revealed that A. ilicifolius, A. leucostachyus and A. mollis contained 113, 112 and 108 unique genes, each of which contained 79, 79 and 74 protein-coding genes, 30, 29 and 30 tRNAs, and 4 rRNA genes, respectively. Differential gene analysis revealed plenty of ndhs gene deletions in the terrestrial plant A. mollis. Nucleotide diversity analysis showed that the psbK, ycf1, ndhG, and rpl22 have the highest nucleotide variability. Compared to A. leucostachyus and A. mollis, seven genes in A. ilicifolius underwent positive selection. Among them, the atpF gene showed a strong positive selection throughout terrestrial to marine evolution and was important for adaptation to coastal intertidal habitats. Phylogenetic analysis indicated that A. ilicifolius has a closer genetic relationship with A. leucostachyus than A. mollis which further confirmed the evolutionary direction of Acanthus going from terrestrial to coastal intertidal zones.
摘要：
Acanthus是一个独特的属，涵盖了三个具有不同生态位的物种，包括Acanthusmollis（干旱陆地），Acanthusleucostashyus（潮湿的森林）和Acanthusilicifolius（沿海潮间带）。这是一个有趣的问题，这些物种如何从陆地进化到沿海潮间带。在本研究中,我们组装了A.ilicifolius的叶绿体基因组，A.leucostachyus和A.ollis，表现出典型的四方结构。大小为150,758,154,686和150,339bp，包含一个大的单拷贝(LSC，82,963、86,461和82,612bp），一个小的单一副本(SSC，17,191、17,511和17,019个基点)，和一对反向重复(IRs，25,302、25,357和25,354bp)，分别。基因注释显示A.ilicifolius，A.leucostachyus和A.mollis包含113、112和108个独特基因，每个包含79、79和74个蛋白质编码基因，30、29和30个tRNA，和4个rRNA基因，分别。差异基因分析显示，陆生植物A.mollis中存在大量ndhs基因缺失。核苷酸多样性分析表明,ycf1,ndhG,和rpl22具有最高的核苷酸变异性。与A.leucostachyus和A.ollis相比，A.ilicifolius中的七个基因进行了阳性选择。其中,atpF基因在整个陆地到海洋的进化过程中显示出很强的正选择，对于适应沿海潮间带生境很重要。系统发育分析表明，与A.leuostachyus相比，A.ilicifolius具有更紧密的遗传关系。这进一步证实了Acanthus从陆地到沿海潮间带的进化方向。
