Li Mingwan, Chen Sufang, Zhou Renchao, Fan Qiang, Li Feifei, Liao Wenbo
Guangdong Key Laboratory of Plant Resources, Key Laboratory of Biodiversity Dynamics, Conservation of Guangdong Higher Education Institutes, Sun Yat-sen UniversityGuangzhou, China.
State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental SciencesBeijing, China.
Front Plant Sci. 2017 May 9;8:704. doi: 10.3389/fpls.2017.00704. eCollection 2017.
Hybridization accompanied by polyploidization and apomixis has been demonstrated as a driving force in the evolution and speciation of many plants. A good example to study the evolutionary process of hybridization associated with polyploidy and apomixis is the genus (Rosaceae), which includes approximately 150 species, most of which are polyploid apomicts. In this study, we investigated all taxa distributed in a small region of Malipo, Yunnan, China. Based on the morphological characteristics, four taxa were identified and sampled: , and a putative hybrid. Flow cytometry analyses showed that was diploid, while the other three taxa were tetraploid. A total of five low-copy nuclear genes and six chloroplast regions were sequenced to validate the status of the putative hybrid. Sequence analyses showed that and are distantly related and they could be well separated using totally 50 fixed nucleotide substitutions and four fixed indels at the 11 investigated genes. All individuals of the putative hybrid harbored identical sequences: they showed chromatogram additivity for all fixed differences between and at the five nuclear genes, and were identical with at the six chloroplast regions. Haplotype analysis revealed that possessed nine haplotypes for the 11 genes, while had ten, and there were no shared haplotypes between the two species. The putative hybrid harbored two haplotypes for each nuclear gene: one shared with and the other with . They possessed the same chloroplast haplotype with . Our study provided convincing evidence for natural hybridization between and , and revealed that all hybrid individuals were derivatives of one initial F1 via apomixes. served as the maternal parent at the initial hybridization event. We proposed that anthropological disturbance provided an opportunity for hybridization between and , and a tetraploid F1 successfully bred many identical progenies via apomixis. Under this situation, species integrity could be maintained for these species, but attentions should be kept for this new-born hybrid.
杂交伴随着多倍体化和无融合生殖已被证明是许多植物进化和物种形成的驱动力。研究与多倍体和无融合生殖相关的杂交进化过程的一个很好的例子是蔷薇科的委陵菜属，该属包括约150个物种，其中大多数是多倍体无融合生殖体。在本研究中，我们调查了分布在中国云南麻栗坡一个小区域内的所有委陵菜属类群。基于形态特征，鉴定并采样了四个委陵菜属类群：云南委陵菜、雪白委陵菜，以及一个推定的杂交种。流式细胞仪分析表明，云南委陵菜是二倍体，而其他三个类群是四倍体。总共对五个低拷贝核基因和六个叶绿体区域进行了测序，以验证推定杂交种的身份。序列分析表明，云南委陵菜和雪白委陵菜亲缘关系较远，在11个研究基因上，利用总共50个固定核苷酸替换和四个固定插入/缺失可以很好地将它们区分开。推定杂交种的所有个体都具有相同的序列：在五个核基因上，它们显示出云南委陵菜和雪白委陵菜之间所有固定差异的色谱叠加性，并且在六个叶绿体区域与云南委陵菜相同。单倍型分析表明，云南委陵菜在11个基因上有9种单倍型，雪白委陵菜有10种，两个物种之间没有共享单倍型。推定杂交种的每个核基因都有两种单倍型：一种与云南委陵菜共享，另一种与雪白委陵菜共享。它们与云南委陵菜具有相同的叶绿体单倍型。我们的研究为云南委陵菜和雪白委陵菜之间的自然杂交提供了令人信服的证据，并揭示所有杂交个体都是通过无融合生殖产生的一个初始F1代的后代。在初始杂交事件中，云南委陵菜作为母本。我们提出，人为干扰为云南委陵菜和雪白委陵菜之间的杂交提供了机会，一个四倍体F1代通过无融合生殖成功繁育了许多相同的后代。在这种情况下，这些委陵菜属物种的物种完整性可以得到维持，但对于这个新产生的杂交种应予以关注。
