Arias Tatiana, Beilstein Mark A, Tang Michelle, McKain Michael R, Pires J Chris
Division of Biological Sciences, University of Missouri, 311 Bond Life Sciences Center, 1201 Rollins Street, Columbia, Missouri 65211 USA.
Am J Bot. 2014 Jan;101(1):86-91. doi: 10.3732/ajb.1300312. Epub 2014 Jan 3.
Cruciferous vegetables, many of which are in the genus Brassica (Brassicaceae), are prized for their nutritive value and have been cultivated for thousands of years. There are numerous wild northwestern Mediterranean species in the tribe Brassiceae, and it is therefore assumed this center of diversity is also the region of origin. Within the tribe, the Nigra and Oleracea clades contain the three diploid Brassica crops, B. oleracea, B. rapa, and B. nigra. These three species hybridized in the past to form the tetraploid crop species B. juncea, B. carinata, and B. napus. Collectively, these crop Brassicas have been thought to be closely related because they can still hybridize.
Using a combination of molecular phylogenetics, diversification analysis, and historical biogeography, we evaluated the relationships and origins of four nested clades: the tribe Brassiceae, the Nigra-Oleracea clade, the core Oleracea (includes B. oleracea + B. rapa and their respective wild relatives), and Brassica oleracea and relatives.
We found evidence that the tribe originated around the intersection forming between the Arabian Peninsula and Saharan Africa approximately 24 million years ago (Mya). Our data also suggest that the maternal genomes of the three diploid crop Brassicas are not closely related and that the Nigra-Oleracea clade diverged 20 Mya. Finally, our analyses indicate that the core Oleracea lineage giving rise to B. oleracea + B. rapa originated ≈3 Mya in the northeastern Mediterranean, from where ancestors of B. oleracea spread through Europe and B. rapa to Asia.
These results challenge previous hypotheses about the biogeographic origins of the tribe Brassiceae and the crop Brassica species and appear to be correlated with major geological and climatic events in the Mediterranean basin.
十字花科蔬菜，其中许多属于芸苔属（十字花科），因其营养价值而备受推崇，并且已经种植了数千年。芸苔族中有许多地中海西北部的野生物种，因此人们认为这个多样性中心也是起源地。在该族中，黑芥属和甘蓝属分支包含三种二倍体芸苔属作物，即甘蓝（B. oleracea）、白菜（B. rapa）和黑芥（B. nigra）。这三个物种过去杂交形成了四倍体作物物种芥菜（B. juncea）、埃塞俄比亚芥（B. carinata）和甘蓝型油菜（B. napus）。总体而言，这些芸苔属作物一直被认为关系密切，因为它们仍然可以杂交。
我们结合分子系统发育学、多样化分析和历史生物地理学，评估了四个嵌套分支的关系和起源：芸苔族、黑芥 - 甘蓝分支、核心甘蓝属（包括甘蓝 + 白菜及其各自的野生近缘种）以及甘蓝及其近缘种。
我们发现有证据表明该族大约在2400万年前（百万年前）起源于阿拉伯半岛和撒哈拉非洲之间形成的交汇处。我们的数据还表明，三种二倍体作物芸苔属的母本基因组并非密切相关，并且黑芥 - 甘蓝分支在2000万年前分化。最后，我们的分析表明，产生甘蓝 + 白菜的核心甘蓝属谱系大约在300万年前起源于地中海东北部，甘蓝的祖先从那里传播到欧洲，白菜的祖先传播到亚洲。
这些结果挑战了先前关于芸苔族和芸苔属作物生物地理起源的假设，并且似乎与地中海盆地的主要地质和气候事件相关。
