Department of Horticulture, Michigan State University, East Lansing, Michigan, 48864, USA.
Ecology, Evolutionary Biology and Behavior, Michigan State University, East Lansing, MI, 48864, USA.
Am J Bot. 2018 Mar;105(3):463-469. doi: 10.1002/ajb2.1040. Epub 2018 Mar 25.
Previous phylogenetic studies employing molecular markers have yielded various insights into the evolutionary history across Brassicales, but many relationships between families remain poorly supported or unresolved. A recent phylotranscriptomic approach utilizing 1155 nuclear markers obtained robust estimates for relationships among 14 of 17 families. Here we report a complete family-level phylogeny estimated using the plastid genome.
We conducted phylogenetic analyses on a concatenated data set comprising 44,926 bp from 72 plastid genes for species distributed across all 17 families. Our analysis includes three additional families, Tovariaceae, Salvadoraceae, and Setchellanthaceae, that were omitted in the previous phylotranscriptomic study.
Our phylogenetic analyses obtained fully resolved and strongly supported estimates for all nodes across Brassicales. Importantly, these findings are congruent with the topology reported in the phylotranscriptomic study. This consistency suggests that future studies could utilize plastid genomes as markers for resolving relationships within some notoriously difficult clades across Brassicales. We used this new phylogenetic framework to verify the placement of the At-α event near the origin of Brassicaceae, with median date estimates of 31.8 to 42.8 million years ago and restrict the At-β event to one of two nodes with median date estimates between 85 to 92.2 million years ago. These events ultimately gave rise to novel chemical defenses and are associated with subsequent shifts in net diversification rates.
We anticipate that these findings will aid future comparative evolutionary studies across Brassicales, including selecting candidates for whole-genome sequencing projects.
先前运用分子标记进行的系统发育研究为 Brassicales 各分支的进化历史提供了多种见解，但许多科之间的关系仍未得到充分支持或尚未解决。最近采用 1155 个核标记的 phylotranscriptomic 方法为 17 科中的 14 科之间的关系提供了可靠的估计。在此，我们报告了利用质体基因组估算的完整科级系统发育关系。
我们对来自 72 个质体基因的 44926bp 的串联数据集进行了系统发育分析，这些基因分布在所有 17 个科的物种中。我们的分析包括另外三个科，即 Tovariaceae、Salvadoraceae 和 Setchellanthaceae，这些科在之前的 phylotranscriptomic 研究中被省略了。
我们的系统发育分析获得了 Brassicales 所有分支的完全解决且得到有力支持的估计。重要的是，这些发现与 phylotranscriptomic 研究中报告的拓扑结构一致。这种一致性表明，未来的研究可以利用质体基因组作为标记来解决 Brassicales 中一些众所周知的困难类群内的关系。我们利用这个新的系统发育框架来验证 At-α 事件在 Brassicaceae 起源附近的位置，中值日期估计值为 3180 万至 4280 万年前，并将 At-β 事件限制在两个节点之一，其中值日期估计值在 8500 万至 9220 万年前之间。这些事件最终产生了新的化学防御，并与随后的净多样化率变化有关。
我们预计这些发现将有助于未来 Brassicales 跨学科的比较进化研究，包括为全基因组测序项目选择候选对象。
