拟南芥DNA探针的比较基因组原位杂交揭示的拟南芥与远缘植物基因组间的同源性

Genomic Homology Between Arabidopsis thaliana and Distantly Related Plants Revealed by Comparative Genomic in situ Hybridization with Arabidopsis DNA Probe

采用生物素标记的拟南芥基因组DNA探针在75%杂交严谨度下对双子叶植物番茄、蚕豆和单子叶植物水稻、玉米、大麦的染色体进行了比较基因组荧光原位杂交(comparative genomic in situ hybridization,cGISH)分析,以揭示拟南芥与远缘植物基因组间的同源性.cGISH信号代表了拟南芥基因组DNA中的重复DNA与靶物种染色体上同源序列的杂交.探针DNA在所有靶物种的全部染色体上都产生了杂交信号.杂交信号为散在分布,并呈现随基因组增大,杂交信号增多,且分布更加分散的趋势.所有靶物种的核仁组织区(NOR)都显示了明显强于其他区域的杂交信号,表明拟南芥基因组DNA探针可用于植物NOR的物理定位.在所有的靶物种中,信号主要分布在染色体的臂中间区和末端,着丝粒或近着丝粒区有少数信号分布.大麦染色体显示了与C-和N-带不同的独特的cGISH信号带型,表明此探针可用于不同植物染色体的识别.这些结果表明,拟南芥基因组与远缘植物基因组之间,除rDNA和端粒重复序列外,还存在其它同源的重复DNA;一些重复DNA序列在被子植物分歧进化为单子叶和双子叶植物之前就已存在,虽经历了长期的进化过程,至今在远缘物种之间仍保持了较高的同源性.结果还提示,大基因组中古老而保守的重复DNA在进化过程中发生了明显的扩增.

Comparative genomic in situ hybridization （cGISH） technology has become a popular approach to study genomic homologies and can be used for the comparison between distant species. In this study, we used biotin-labeled Arabidopsis genomic DNA to hybridize the chromosomes from two dicots （Lycopersicon esculentum and Vicia faba ） and three monocots （ Oryza sativum ssp. indica , Zea mays and Hordeum vulgare ） at 75 % stringency, in order to evaluate the genomic homologies between Arabidopsis and distantly related plants. We found the fluorescent hybridization signals appeared to be dispersed within the chromosomes in all observed soecies, and displayed an increasing as the genome size of a species becomes larger. Strong hybridizations were observed at the nucleolar organizing regions （NORs） in all species studied, which indicates the corresponding Arabidopsis DNA probes could potentially be applied for NOR mapping in plants. In all analyzed species, hybridization signals primarily located at the interstitial sites or chromosomal ends, whereas only a few detected in centromeric or pericentromeric regions. The patterns of cGISH signals represented with a different profile as compared to the chromosome C- or N-banding patterns in a particular species. Therefore it might be used as alternative measurement to enable the discrimination of individual chromosomes in plants. Our results have demonstrated the existence of numerous homologous repetitive DNA sequences between Arabidopsis and distantly related plants besides rDNA and telomeric repeats, and a significant portion of them are presumably stabilized before the divergence of dicotyledon and monocotyledon during evolution. Moreover, the results also supported the discovery of considerable amplifications of ancient conserved repetitive DNAs as large plant genomes developed during evolution.