新麦草基因组重复序列组成及在赖草属物种染色体上的分布

Composition of the Genome Repeat Sequences of Psathyrostachys juncea and Its Distribution on the Chromosomes in Leymus Species

新麦草(Psathyrostachys juncea)被认为是赖草属植物的一个重要祖先物种。对新麦草中高度重复序列Cot-1 DNA文库克隆测序分析鉴定,结果表明新麦草Cot-1 DNA文库中的序列可以分为6种类型:反转座子、转座子、卫星DNA、抗病相关LZ-NBS-LRR、未能鉴定类型、反转座子LTR和LTR/Copia类型序列组合型,占比分别为49.5%、1.0%、28.7%、5.9%、13.9%和1.0%。进一步利用2种卫星DNA序列和5个反转座子序列为探针,对新麦草、赖草(Leymus secalinus)和2个大赖草(L. racemosus)材料进行染色体荧光原位杂交,结果表明卫星DNA序列TaiI-family和pSc250-family杂交信号主要分布在染色体的端部,TaiI-family杂交信号数量分别为20、16、7和18,而卫星DNA序列pSc250-family在新麦草、赖草中的杂交信号数量分别为17和24,在2个大赖草材料均没有信号检出。反转座子序列在3个物种染色体上基本呈散布分布方式,而且在赖草属物种染色体分布呈现同质化倾向,其中克隆序列pPj-44和pPj-28在新麦草和赖草属物种间信号分布差异显著,分别提示在异源多倍化过程中存在序列扩张和收缩,克隆序列pPj-77仅在1个大赖草材料10个染色体杂交信号强度区别于其余染色体。研究结果表明,新麦草重复序列在赖草多倍体形成过程发生了快速进化并可能存在同质化扩散,同时赖草属不同物种基因组间重复序列组成可能存在显著差异。

Psathyrostachys juncea was considered an important ancestral species of Leymus.The genomic Cot-1 DNA library with highly repeat sequences of Psa.juncea was constructed,and sequenced and characterized,and the results showed that the library could be classified into six types:retrotransposons,transposons,satellite DNA,LZ-NBS-LRR,uncharacterized sequences,and retrotransposon LTR mixed LTR/Copia,and the proportions were 49.5%,1.0%,28.7%,5.9%,13.9%and 1.0%of the Cot-1 DNA,respectively.Furthermore,two satellite DNAs and five retrotransposon sequences were used as probes,and chromosomes in Psa.juncea,Leymus secalinus and L.racemosus were detected by florescence in situ hybridization(FISH).The results showed that the hybridization signals of satellite DNA sequences TaiI-family and pSc250-family were mainly distributed at the ends of chromosomes,and the number of TaiI-family hybridization signals were 20,16,7,and 18 in Psa.juncea,L.secalinus,L.racemosus(PI 531811)and L.racemosus(PI 531812),respectively,and the number of pSc250-family hybridization signals were 17 and 24 in Psa.juncea and L.secalinus,respectively,but no signal was detected in two L.racemosus samples.The distribution of retrotransposon sequences on the chromosomes of three detected species was basically dispersed,and the distribution of chromosome sequences in Leymus species showed a tendency of homogenity.Especially,clone sequences pPj-44 and pPj-28 showed significant differences in signal distribution between Psa.juncea and Leymus species,suggesting sequence expansion and contraction,respectively,during allopolyploidization,and clone sequence pPj-77 only differentiated the hybridization intensity of 10 chromosomes from the rest of the chromosomes in one L.racemosus(PI 531812).The results suggested the repeats of Psa.juncea evolved rapidly and had homogenous diffusion during the polypoid formation of Leymus species and the repeat composition might be significant different among different Leymus species.