利用叶绿体基因组数据解析锦葵科梧桐亚科的系统位置和属间关系

Plastid phylogenomics resolving phylogenetic placement and genera phylogeny of Sterculioideae(Malvaceae s.l.)

分子系统学研究将传统梧桐科与锦葵科、木棉科和椴树科合并为广义锦葵科,并进一步分为9个亚科。然而,9个亚科之间的关系尚未完全明确,且梧桐亚科内的属间关系也未得到解决。为了明确梧桐亚科在锦葵科中的系统发育位置,厘清梧桐亚科内部属间系统发育关系,该研究对锦葵科8个亚科进行取样,共选取55个样本,基于叶绿体基因组数据,采用最大似然法和贝叶斯分析构建系统发育树。结果表明:(1)广义锦葵科中,刺果藤亚科和扁担杆亚科组成Byttneriina分支,Malvadendrina分支中山芝麻亚科为其他亚科的姐妹群,随后分出梧桐亚科(WCG、LSC和SSC矩阵构成的数据集),以及Malvatheca分支(木棉亚科和锦葵亚科)与非洲芙蓉亚科-椴树亚科的姐妹关系。(2)在梧桐亚科中,可乐果属分支(Cola clade)是独立一支,随后是酒瓶树属分支(Brachychiton clade)与苹婆属分支(Sterculia clade)+银叶树属分支(Heritiera clade)形成姐妹关系(WCG、LSC和CDS矩阵)。(3)在可乐果属分支中,可乐果属为梧桐属(含闭果桐属)和胖大海属+舟翅桐属的姐妹群。该研究基于叶绿体基因组数据基本澄清了广义锦葵科的亚科系统关系以及梧桐亚科内各属关系,系统发育树框架基本明晰,但梧桐亚科在Malvadendrina分支的位置和酒瓶树属在梧桐亚科的位置,以及梧桐属的概念及范围仍需进一步研究,尤其是结合核基因组数据进行分析。

Phylogenetic analyses supported that four traditionally defined families Sterculiaceae,Tiliaceae,Bombacaceae and Malvaceae were subsumed into Malvaceae s.l.and nine subfamilies had been recognized within Malvaceae s.l.However,phylogenetic relationships among the nine subfamilies were not well resolved.Moreover,phylogenetic relationships among genera were also not clear in Sterculioideae.In this study,we reconstructed phylogenetic trees of Malvaceae s.l.based on chloroplast genome sequences from 55 species that representing eight recognized subfamilies for clarifying phylogenetics relationships of subfamilies and Sterculioideae.The results were as follows:(1)Byttnerioideae and Grewioideae formed the Byttneriina clade in Malvaceae s.l.as sister to the Malvadendrina clade which by having Helicteroideae as the first divergent subfamily,followed by Sterculioideae(WCG,LSC and SSC datasets),and the Malvatheca clade(Bombacoideae+Malvoideae)and the clade Dombeyoideae+Tilioideae as sister.(2)The Cola clade was the first divergent clade in Sterculioideae,then the Brachychiton clade was sister to the clade Sterculia+Heritiera(WCG,LSC and CDS datasets).(3)In the Cola clade,Cola+Octolobus+Pterygota were the first divergent group,then Firmiana spp.(including Hildegardia)were sister to the clade Scaphium+Pterocymbium.In this study,plastid phylogenomic analyses have well resolved the phylogenetic framework of subfamilies in Malvaceae s.l.,and phylogenetic relationship among genera in Sterculioideae.However,phylogenetic positions of Sterculioideae in the Malvadendrina clade and Brachychiton in Sterculioideae,respectively,as well as the concept and circumscription of Firmiana,need to confirm and further investigate using nuclear genomic data in the future.