Chacón Juliana, Madriñán Santiago, Debouck Daniel, Rodriguez Fausto, Tohme Joe
Laboratorio de Botánica y Sistemática, Universidad de los Andes, Apartado Aéreo 4976, Bogotá, D.C., Colombia.
Mol Phylogenet Evol. 2008 Oct;49(1):260-7. doi: 10.1016/j.ympev.2008.07.015. Epub 2008 Jul 31.
From a phylogenetic perspective, the genus Manihot can be considered as an orphan group of plants, and the scientific knowledge acquired has been mainly related to cassava, one of the most important crops in poor tropical countries. The goal of the majority of evolutionary studies in the genus has been to decipher the domestication process and identify the closest relatives of cassava. Few investigations have focused on wild Manihot species, and the phylogeny of the genus is still unclear. In this study the DNA sequence variation from two chloroplast regions, the nuclear DNA gene G3pdh and two nuclear sequences derived from the 3'-end of two cassava ESTs, were used in order to infer the phylogenetic relationships among a subset of wild Manihot species, including two species from Cnidoscolus as out-groups. Maximum parsimony and Bayesian analyses were conducted for each data set and for a combined matrix due to the low variation of each region when analyzed independently. A penalized likelihood analysis of the chloroplast region trnL-trnF, calibrated with various age estimates for genera in the Euphorbiaceae extracted from the literature was used to determine the ages of origin and diversification of the genus. The two Mesoamerican species sampled form a well-defined clade. The South American species can be grouped into clades of varying size, but the relationships amongst them cannot be established with the data available. The age of the crown node of Manihot was estimated at 6.6 million years ago. Manihot esculenta varieties do not form a monophyletic group that is consistent with the possibility of multiple introgressions of genes from other wild species. The low levels of variation observed in the DNA regions sampled suggest a recent and explosive diversification of the genus, which is confirmed by our age estimates.
从系统发育的角度来看，木薯属可被视为植物中的一个孤立类群，目前所获得的科学知识主要与木薯有关，木薯是热带贫困国家最重要的作物之一。该属大多数进化研究的目标是破解驯化过程并确定木薯的近亲。很少有研究关注野生木薯物种，该属的系统发育仍不清楚。在本研究中，使用了来自两个叶绿体区域的DNA序列变异、核DNA基因G3pdh以及源自两个木薯EST 3'端的两个核序列，以推断一部分野生木薯物种之间的系统发育关系，包括来自刺萼龙葵属的两个物种作为外类群。由于每个区域单独分析时变异程度较低，因此对每个数据集以及一个组合矩阵进行了最大简约法和贝叶斯分析。利用从文献中提取的大戟科各属的各种年龄估计值校准的叶绿体区域trnL-trnF的惩罚似然分析，来确定该属的起源和多样化年龄。所采样的两个中美洲物种形成了一个明确的分支。南美洲的物种可以分为不同大小的分支，但根据现有数据无法确定它们之间的关系。木薯属冠节点的年龄估计为660万年前。木薯品种并未形成一个单系类群，这与来自其他野生物种的基因多次渗入的可能性是一致的。在所采样的DNA区域中观察到的低变异水平表明该属近期经历了快速的多样化，这一点得到了我们的年龄估计的证实。
