赖草基因组重复序列组成及染色体分布特性

Characterization of genome repeat sequence composition and chromosomal distribution in Leymus secalinus

【目的】赖草属植物是麦类作物遗传改良和育种的重要基因资源,但作为异源多倍体植物,其基因组来源仍存在较大争议。通过比较赖草、大赖草及新麦草基因组中重复序列分布,探索赖草属物种基因组来源以及种间基因组多样性的形成特性。【方法】通过构建赖草属物种赖草的Cot-1 DNA文库获得大量重复序列,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-1 DNA可归为串联重复序列、散布重复序列、散布加串联混合重复序列以及未能鉴定类型,4种类型占比分别为32.4%、45.7%、12.4%和9.5%。(2)串联重复序列TaiI-family、Lt1-6、pTa-535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7~20,1~14,17~26,0~24个。(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: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;在所有染色体的所有区域都有分布;在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,但在信号强度以及部分染色体上的分布方式存在多态性。【结论】赖草属物种中的一些重复序列具有快速进化的特性,支持赖草属物种多倍化过程,并存在散在重复序列向整个核基因组的快速同质化扩散。

[Objective]Leymus Hochst.stands as a crucial genetic resource for the genetic improvement and breeding of cereal crops.However,as allopolyploid plants,their genome origin remains unclear.This study aims to explore the genomic origin of the species in Leymus secalinus and the characteristics of inter-species genomic diversity by comparing the distribution of the repetitive sequences in the genomes of L.secalinus,L.racemosus,and Psathyrostachys juncea.[Methods]Genomic Cot-1DNA library of L.secalinus was constructed,and clones were sequenced and analyzed.The repetitive sequences were mapped to the chromosome of L.secalinus,L.racemosus,and P.juncea by fluorescence in situ hybridization(FISH).[Results](1)The repetitive sequences of the Cot-1 DNA of L.secalinus were classified into 4 types based on their expected genomic distribution patterns:Tandem repeats,dispersed repeats,tandem mixed dispersed repeats,and uncharacterized repeats,representing 32.4%,45.7%,12.4%,and 9.5%,respectively.(2)The number of the hybridization sites of the tandem repeats TaiI-family,Lt1-6,pTa-535,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.Hybridizations were distributed in centromere,pericentromere,and intercalary regions in all chromosomes.Hybridizations were distributed in all the chromosomes.Hybridizations were distributed the same as the pattern 1 except some chromosomes were carrying telomeric hybridizations.Two LTR/copia sequences were detected only in L.secalinus,while the others were detected in all species and accessions tested but with polymorphisms in hybridization intensities or hybridization patterns in partial chromosomes.[Conclusion]Some of the repetitive sequences in Leymus species may have the characteristics of rapid evolution,which supports the rapid homogenization spread of scattered repetitive sequences to the entire nuclear genome during the polyploidy of Leymus species.