种间杂种染色体配对所揭示的披碱草属植物StY基因组分化及其进化意义

在同倍体(homoploid)植物杂交-分化的物种形成(speciation)过程中，杂交后代与亲本之间的有效生殖隔离是新物种形成的关键。杂种与亲本在时间、空间、生态环境和基因水平上的隔离，保证了杂种后代的分化和稳定，并逐渐形成新物种。为了研究披碱草属(Elymus)含StY基因组四倍体物种的系统演化关系，本文对来自亚洲不同地理分布区的26种披碱草属植物进行了大规模的种间杂交和杂种F1减数分裂染色体配对行为的分析。结果表明各物种之间有不同程度的杂交亲合力，杂交结实率在各杂交组合之间有较大的变异(在4．8％-100％之间)；但各物种之间的杂种F1完全不育。证明各物种之间形成了明显的生殖隔离。种间杂种F1减数分裂中期-I染色体配对分析的结果进一步表明，StY基因组随各披碱草属物种地理分布的不同而有不同程度的分化。来自同一分布区(如东亚或西亚分布区之内)物种的StY基因组分化程度较低，但来自不同分布区(如东亚和西亚)物种之间相同的StY基因组具有显著的分化。表明地理隔离对含StY基因组物种的分化起到了十分重要的作用。通过对种间和种内杂种F1的减数分裂异常现象和染色体配对频率变化规律的分析，作者认为细胞学水平的变化，如基因组同源性的分化和染色体结构的变异等都在杂种后代与亲本之间产生生殖隔离并逐渐形成新物种的进化过程中起到了积极的作用。

Differentiation of the StY genomes in Elymus species as referred by meiotic pairing in interspecific hybrids and its evolutionary significance

Hybridization-differentiation is a major pathway of speciation and the active force of plant evolution, including homoploid speciation without change of chromosome numbers. Effective isolation between parental species and their hybrid derivatives plays an essential role in homoploid speciation for stabilizing a newly formed species. Studies of isolation mechanisms will facilitate our understanding of the speciation process. The genus Elymus of Triticeae ( Poaceae) includes ca. 150 polyploid species with different genomes, viz. the StH, St Y , StHY, StPY, and StWY from different origins, providing an ideal group for studying mechanisms of polyploid and homoploid speciation. There are about 30 tetraploid species containing the StY genomes distributed in temperate Asia and the eastern margin of Europe. In order to study genomic relationships of the StY Elymus species, samples representing 26 species collected from Western through Eastern Asia were extensively hybridized with each other. Meiotic pairing at metaphase-I of the intra- and interspecific hybrids was analyzed, which revealed a significant differentiation pattern in hornology of the StY genomes among Elymus species studied. Species from the same regions, e. g. within eastern or western Asia, shared the StY genomes with a relatively low level of differentiation, but species from different regions, e. g. between eastern and western Asia, shared substantially differentiated StY genomes. Species from Central Asia contained intermediately differentiated StY genomes compared with those from western and eastern Asia. The discovery of geographical differentiation of the StY genomes in tetraploid Elymus species has significance for study of evolutionary processes and mechanisms of homoploid speciation in Elymus. In addition to other well-recognized factors responsible for the isolation between parental species and their hybrid derivatives during the hybridization-differentiation process ( such as temporal, spatial, genie , and ecological isolation) , the authors believe that meiotic irregularity caused by genomic differentiation between species also provides an important mechanism for homoploid speciation.