赖草基因组重复序列组成及染色体分布特性

【目的】赖草属植物是麦类作物遗传改良和育种重要的基因资源，但作为异源多倍体植物，关于其基因组来源仍存在较大争议。【方法】通过构建赖草属物种赖草的Cot-1DNA文库，获得大量重复序列，进一步利用荧光原位杂交技术和重复序列对赖草，以及近缘物种大赖草和祖先供体物种新麦草进行染色体荧光原位杂交涂染。【结果】（1）根据序列及基因组分布特性，赖草Cot-1DNA可归为串联重复序列（TaiI、Lt1-6、pTa535和pSc250家族），散布重复序列（LTR/Gypsy、LTR/Copia、LTR及转座子），散布加串联混合重复序列（LTR+Afa-family和N8-family+LZ-NBS-LRR）以及未能鉴定类型，4种类型在Cot-1DNA文库克隆中的占比分别为32.4%、45.7%、12.4%和9.5%。（2）串联重复序列TaiI、Lt1-6、pTa535和pSc250在不同物种及同一物种不同材料间信号数量存在较大变异，分别为7~20、1~14、17~26及0~24。（3）10个反转座子序列在所有物种染色体的分布呈现3种方式：第1种是在所有染色体上杂交信号集中分布在着丝粒、近着丝粒及间质区；第2种是在所有染色体的所有区域都有分布；第3种为大部分染色体上的分布方式与第1种相同，但是部分染色体端部也有分布。2个LTR/Copia序列仅在赖草染色体上有分布，其他序列在不同物种以及不同材料间均有分布，但是在信号强度以及部分染色体上的分布方式等存在多态性。【结论】赖草属物种中的一些重复序列可能具有快速进化的特性，支持赖草属物种多倍化过程中，可能存在散在重复序列向整个核基因组的快速同质化扩散。

Characterization of repetitive sequences in Leymus secalinus and chromosomal distribution in related species

[Objective] Leymus Hochst stands as a crucial genetic resource for the genetic improvement and breeding of cereal crops. However, as allopolyploids, their genome origin remains unclear. [Methods] Genomic Cot-1DNA library of Leymus secalinu was constructed, clones of which were sequenced and analyzed. A few of repetitive sequences were physically mapped in chromosomes of L. secalinus, L. racemousus, and Psathyrostachy juncea by Fluorescence in situ hybridization (FISH). [Results] (1)The repetitive sequences of the Cot-1DNA of L. secalinus could be classified into 4 types based on their expected genomic distribution patterns, tandem repeats (TaiI, Lt1-6, pTa535 and pSc250 family), dispersed repeats (retrotransposable LTR and transposable elements), tandem mixed dispersed repeats (LTR plus Afa-family and N8-family plus LZ-NBS-LRR), and uncharacterized repeats, and which represented 32.4%, 45.7%, 12.4% and 9.5% of the Cot-1DNA, respectively. (2) The hybridization sites number of tandem repeats TaiI, Lt1-6, pTa535 and pSc250 were highly varied from 7-20, 1-14, 17-26 and 0-24 respectively, across different species and accessions. (3) Ten LTR repeats hybridized the tested species chromosomes mainly by 3 patterns: First, hybridizations distributed in centromere, pericentromere, and intercalary regions in all chromosomes. Second, hybridizations were all over the chromosomes. Third, Hybridizations were as the same as the pattern 1 except a few chromosomes carrying telomeric hybridizations. Two LTR/copia sequences were detected only in L. secalinus, while the others were detected in all tested species and accessions but with polymorphisms in hybridization intensities or hybridization patterns in partial chromosomes. [Conclusion] The results suggested rather fast-evolving repetitive sequences in Leymus genome, and supported hypothesis that the dispersed elements must have spread across genomes, thus homogenizing the nuclear genomes of Leymus during the allopolyploidization process.