海三棱藨草及其近缘种基因组大小的测定

Genome size determination of Scirpus mariqueter and its related species

关键词:  流式细胞术, 基因组大小, 基因组Survey分析, 海三棱藨草, 藨草属

Key words:  flow cytometry, genome size, genome Survey analysis, Scirpus mariqueter, Scirpus

摘要:

基因组大小是物种基因组的重要特征,通常用DNA C值来衡量,能够用于快速判断基因组倍性,并为分类学与进化生物学提供重要依据。海三棱藨草(Scirpus mariqueter)是长江口和杭州湾具有重要生态意义的标志性物种,被认为是扁秆藨草(S. planiculmis)和藨草(S. triqueter)的杂交种,因染色体小而难以准确确定倍性。近年来,部分研究者指出该物种的分类和命名存在疑点。该研究通过基因组Survey分析检测海三棱藨草样本CJ1的基因组特征,测序深度约为120 ×,并以绿豆(Vigna radiata)为参考标准,利用流式细胞术测定了海三棱藨草及其同域近缘种扁秆藨草和藨草以及海三棱藨草和扁秆藨草的杂交F1共13个样本的DNA C值和相对倍性。结果表明:(1)基因组Survey分析测得CJ1的基因组大小为244.12 Mbp,杂合率为0.68%,重复序列比例为42.38%,GC含量为37.25%。(2)流式细胞术测得来自不同区域的海三棱藨草各样本的基因组倍性相同,1C值在234.87 ～ 242.5 Mbp之间,其中CJ1的基因组大小与基因组Survey检测结果高度一致。(3)扁秆藨草的1C值在251.77 ～ 264.13 Mbp之间,藨草1C值为537.33 Mbp。根据上述基因组大小,认为海三棱藨草不可能是这两者的杂交种。该研究补充了海三棱藨草及其近缘种的基因组特征,为后续全基因组测序奠定基础,同时也否定了海三棱藨草起源于扁杆藨草和藨草杂交的假说。

Abstract:

Genome size is an important feature of a species' genome and is usually measured by the DNA C-value, which can be used for quickly testing genome ploidy and provide an important basis for taxonomy and evolutionary biology. Scirpus mariqueter is a species with important ecological effects in the Yangtze River estuary and Hangzhou Bay, China. It is considered as a hybrid of S. planiculmis and S. triqueter, and it is difficult to accurately determine ploidy due to its small chromosomes. However, in recent years, some researchers, based on molecular markers, have raised doubts about the classification and nomenclature of S. mariqueter. Therefore, more experimental evidence on the taxonomic attributes, genomic characteristics and possible ploidy variation of S. mariqueter and its related species is needed. In this study, the genomic characteristics of S. mariqueter sample CJ1 were determined by genome survey analysis with a sequencing depth of approximately 120 ×. The DNA C-value and relative ploidy of 13 samples of S. mariqueter and its sympatric, related species(S. triqueter and S. planiculmis)were estimated by flow cytometry with Vigna radiata as a reference. The results were as follows:(1)Genome Survey analysis showed that the genome size of CJ1 was 244.12 Mbp, with a 0.68% heterozygosity rate, 42.38% sequence repeat, and 37.25% GC content.(2)The flow cytometry results showed that the ploidy of S. mariqueter samples from different regions was the same, with 1C values ranging from 234.87 Mbp to 242.5 Mbp, and the genome size of CJ1 was highly consistent with the genome Survey results.(3)The 1C value of S. planiculmis was between 251.77 Mbp and 264.13 Mbp, and the 1C value of S. triqueter was 537.33 Mbp. Because the genome size of hybrids is usually between or larger than those of their parents, it is unlikely that S. mariqueter is a hybrid of the two species based on the abovementioned genome size. This study provides genomic characteristics of S. mariqueter and its related species and lays a foundation for its whole-genome sequencing. At the same time, it also rejects the hypothesis that S. mariqueter originated from hybridization between S. planiculmis and S. triqueter.