赖草属物种的ITS序列变异及其系统推断
摘要
赖草属Leymus Hochst是禾本科Poaceae小麦族Triticeae (Poaceae)的一个重要多年生属,全世界有赖草属大约32种19亚种,从北极寒温带到南亚热带均有分布。细胞遗传学研究表明赖草属植物存在四倍体(2n=4x=28)至十二倍体(2n=12x=84)染色体倍性变化。该属植物的大多数物种为草原和草甸的主要组成成分,许多还是优良的牧草,具有较高的伺用价值。因此,作为现在和将来麦类作物育种的重要三级基因源,赖草属植物对改良遗传基础日益狭窄的麦类作物具有重要意义。然而,有关该属植物的起源、系统地位、物种界限、种间(内)亲缘关系等问题,仍然存在较大的分歧。本研究利用nrDNA ITS序列,对赖草属(NsXm)及近缘属新麦草属(Ns)、拟鹅观草属(St)、Lophopyrum elongatum (Ee)、Thinopyrun bessarabicum (Eb)、Eremopyrum triticeum (F)和冰草属(P)共7个类群的16份植物材料进行了系统发育重建及ITS序列遗传多样性分析,主要结果如下：
1、在基于ITS序列构建的系统发育树中,绝大多数赖草属植物都与新麦草属植物聚为一支,表明赖草属植物与新麦草属关系密切,支持赖草属植物的Ns基因组来源于新麦草属。不同的赖草属植物分别与不同的新麦草属植物聚在一起,暗示可能不同的新麦草植物参与了不同的赖草属物种以及同一赖草属物种的不同类群的的物种形成。
2、Leymus arenarius与Leymus racemosus二者亲缘关系较近,可能通过不同的染色体加倍或者杂交,或从共同的祖先起源。7个赖草属物种中只有L.triticoides和L. duthiei的所有克隆分别形成单系。可能是因为处于北美的L.triticoides由于地理位置分布与其他大部分分布在中亚或欧亚的赖草属植物相隔甚远,而L. duthiei生长在林下,颖退化,在长期的进化过程中形成了相对独立的状态,因此形成单独分支。
3、系统发育树显示,同一物种的不同克隆并不总是聚在一起,反映了赖草属植物的ITS序列存在较大的遗传分化。赖草属植物分布广、物种类群和数量多及染色体倍性高可能导致了其存在大的遗传分化。
4、Leymus arenarius和L. tianschanicus与Agropyron cristatum、Ag. mongolicum (P)和Eremopyrum triticeum (F)亲缘关系较近,F和P基因组物种可能是赖草属植物的Xm基因组供体。
5、赖草属植物种内ITS序列多态性估计和种间分化程度显示赖草属植物ITS的遗传变异较大,ITS具有明显的遗传多样性。
Leymus Hochst. is a perennial gemus of grass in the tribe Triticeae (Poaceae) There are about 32 species and 19 subspecies in Leymus. They are distributed in the temperate regions of Eurasia, North and South America, extending to the subtropic and the tropic alpine regions. All the species are polyploids with the chromosome numbers ranging from 2n=4x=28 to 2n=12x=84. Many species of Leymus are not only main components of grasslands and grass marshlands, but also fine varieties of herbage and forge. Being an important genetic resource, Leymus is significant to the improvement of Triticeae cereal crops. However, the origin and definition of the genus, precise taxonomic ranks and relationships among the species in the genus have been under discussion. In this study, seven Leymus species and their nine related species were reconstructed base on nrDNA ITS. The main results showed as follows:
1. In the ITS trees, most of the Leymus species and Psathyrostachys species are in the same clade, which suggested that Leymus species derived their Ns genome from Psathyrostachys species. Different Leymus species clustered with different Psathyrostachys species indicated that Psathyrostachys species served as the donor to different Leymus species.
2. Leymus arenarius is closely related to L. racemosus which may adopt different chromosome doubling or hybridization, or origin from common ancestor. Only the clones of L. triticoides and L. duthiei were monophyletic. The possible reason is L. triticoides from North America is far from most other Leymus species distributed in Central Asia or Eurasia, while L. duthiei is growing in the understory, formating a relatively independent status in long-term evolution.
3. Phylogenetic tree shows that different clones of the same species are not always together, reflecting a big genetic differentiation of ITS sequences in Leymus species. The widely distribution, large numbers and high ploidy may lead to the big genetic differentiation.
4. Leymus arenarius and L. tianschanicus had the close relationship with Agropyron cristatum、Ag. mongolicum (P) and Eremopyrum triticeum (F). F and P genomes might be the donor of Xm genome of Leymus species.
5. The estimates of nucleotide diversity for ITS sequences within Leymus species showed a big genetic variation and diversity in ITS sequences.
1、在基于ITS序列构建的系统发育树中,绝大多数赖草属植物都与新麦草属植物聚为一支,表明赖草属植物与新麦草属关系密切,支持赖草属植物的Ns基因组来源于新麦草属。不同的赖草属植物分别与不同的新麦草属植物聚在一起,暗示可能不同的新麦草植物参与了不同的赖草属物种以及同一赖草属物种的不同类群的的物种形成。
2、Leymus arenarius与Leymus racemosus二者亲缘关系较近,可能通过不同的染色体加倍或者杂交,或从共同的祖先起源。7个赖草属物种中只有L.triticoides和L. duthiei的所有克隆分别形成单系。可能是因为处于北美的L.triticoides由于地理位置分布与其他大部分分布在中亚或欧亚的赖草属植物相隔甚远,而L. duthiei生长在林下,颖退化,在长期的进化过程中形成了相对独立的状态,因此形成单独分支。
3、系统发育树显示,同一物种的不同克隆并不总是聚在一起,反映了赖草属植物的ITS序列存在较大的遗传分化。赖草属植物分布广、物种类群和数量多及染色体倍性高可能导致了其存在大的遗传分化。
4、Leymus arenarius和L. tianschanicus与Agropyron cristatum、Ag. mongolicum (P)和Eremopyrum triticeum (F)亲缘关系较近,F和P基因组物种可能是赖草属植物的Xm基因组供体。
5、赖草属植物种内ITS序列多态性估计和种间分化程度显示赖草属植物ITS的遗传变异较大,ITS具有明显的遗传多样性。
Leymus Hochst. is a perennial gemus of grass in the tribe Triticeae (Poaceae) There are about 32 species and 19 subspecies in Leymus. They are distributed in the temperate regions of Eurasia, North and South America, extending to the subtropic and the tropic alpine regions. All the species are polyploids with the chromosome numbers ranging from 2n=4x=28 to 2n=12x=84. Many species of Leymus are not only main components of grasslands and grass marshlands, but also fine varieties of herbage and forge. Being an important genetic resource, Leymus is significant to the improvement of Triticeae cereal crops. However, the origin and definition of the genus, precise taxonomic ranks and relationships among the species in the genus have been under discussion. In this study, seven Leymus species and their nine related species were reconstructed base on nrDNA ITS. The main results showed as follows:
1. In the ITS trees, most of the Leymus species and Psathyrostachys species are in the same clade, which suggested that Leymus species derived their Ns genome from Psathyrostachys species. Different Leymus species clustered with different Psathyrostachys species indicated that Psathyrostachys species served as the donor to different Leymus species.
2. Leymus arenarius is closely related to L. racemosus which may adopt different chromosome doubling or hybridization, or origin from common ancestor. Only the clones of L. triticoides and L. duthiei were monophyletic. The possible reason is L. triticoides from North America is far from most other Leymus species distributed in Central Asia or Eurasia, while L. duthiei is growing in the understory, formating a relatively independent status in long-term evolution.
3. Phylogenetic tree shows that different clones of the same species are not always together, reflecting a big genetic differentiation of ITS sequences in Leymus species. The widely distribution, large numbers and high ploidy may lead to the big genetic differentiation.
4. Leymus arenarius and L. tianschanicus had the close relationship with Agropyron cristatum、Ag. mongolicum (P) and Eremopyrum triticeum (F). F and P genomes might be the donor of Xm genome of Leymus species.
5. The estimates of nucleotide diversity for ITS sequences within Leymus species showed a big genetic variation and diversity in ITS sequences.
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