School of Biological Science and Technology, Liupanshui Normal University, Liupanshui, 553004, China.
Funct Integr Genomics. 2024 Mar 22;24(2):64. doi: 10.1007/s10142-024-01344-9.
Pittosporum (Pittosporaceae) is famous as the ornamental and medical values, which is distributed tropical and subtropical regions of Eastern Hemisphere. The few phylogenetic studies have included samples from the Pacific Island, but the phylogenetic relationships of Asian species has not been studied. Here, the complete chloroplast (cp) genomes of ten Pittosporum species from East Asia were first sequenced and compared with those of the published species of this genus. Our results indicated that cp genomes of these species had a typical and conserved quadripartite structure. 131 genes were identical in order and orientation and no changes of inverted repeat (IR) occurred. However, the comparative analysis of cp genomes suggested that sequence divergence mainly appeared in non-coding or intergenic regions, in which several divergence hotspots were identified. By contrast, protein-coding genes showed the lowest variance under strong purifying selection. Phylogenetic analysis based on the cp genome sequences showed that the tested Pittosporum species were clustered into two major clades, in which the Asian species formed Clade I and the remaining species from Australia and New Zealand formed Clade II with high support values, which was consistent with the results of ITS data with low support values. These results suggested that cp genome is a robust phylogenetic indicator for deep nodes in the phylogeny of Pittosporum. Meanwhile, these results will provide the valuable information to better understand the phylogeny and biogeography of Pittosporum.
海桐花属（海桐花科）以其观赏和药用价值而闻名，分布于东半球的热带和亚热带地区。少数系统发育研究包括来自太平洋岛屿的样本，但亚洲物种的系统发育关系尚未得到研究。在这里，首次对东亚的 10 种海桐花属植物的完整叶绿体基因组进行了测序，并与该属已发表的物种的基因组进行了比较。我们的结果表明，这些物种的叶绿体基因组具有典型的、保守的四分体结构。131 个基因在顺序和方向上是相同的，没有发生反向重复（IR）的变化。然而，叶绿体基因组的比较分析表明，序列差异主要出现在非编码区或基因间区，其中确定了几个分歧热点。相比之下，蛋白质编码基因在强烈的纯化选择下表现出最低的变异。基于叶绿体基因组序列的系统发育分析表明，所测试的海桐花属植物聚为两个主要分支，其中亚洲物种形成分支 I，其余来自澳大利亚和新西兰的物种形成分支 II，支持值很高，与低支持值的 ITS 数据结果一致。这些结果表明，叶绿体基因组是海桐花属系统发育中深节点的稳健系统发育指标。同时，这些结果将为更好地理解海桐花属的系统发育和生物地理学提供有价值的信息。
