The determination of the ploidy level of an organism is a prerequisite for studies of evolution, cellular function, and genomic construction. Identification of the ploidy of the economically important red alga Gracilariopsis lemaneiformis has been hindered by its small genome and large number of chromosomes. Therefore, in the current study, PloidyNGS, a tool that calculates the number of reads supporting different alleles at each position along the genome sequence, and fluorescence in situ hybridization coupled with tyramide signal amplification (TSA‐FISH) were used to clarify the ploidy of G. lemaneiformis. In addition, flow cytometry (FCM) was used to estimate the ploidy of different somatic cells. The PloidyNGS results showed that most of the alleles in the gametophyte were monomorphic, whereas the TSA‐FISH results showed that one hybridization signal was observed in gametophytic nuclei and two in tetrasporophytic nuclei when the nuclei were hybridized by single copy gene probes. These results confirmed that G. lemaneiformis is a haploid in the gametophytic generation and diploid in the sporophytic generation. Moreover, the FCM result suggested that G. lemaneiformis was not an endopolyploid. Based on previous studies, we hypothesize that the nuclear number is important for the cellular differentiation and function of this species. We also suggest that G. lemaneiformis evolved from a paleopolyploid, the genome of which has been diploidized, and that traces of genomic doubling are no longer apparent. Thus, this study provides important evidence for further studies on the evolution and genomes of red algae.

中文翻译：

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在细胞和基因组水平上估计拟南芥的倍性。

确定生物的倍性水平是研究进化，细胞功能和基因组构造的先决条件。经济上重要的红藻Gracilariopsis lemaneiformis的倍性鉴定受到阻碍，因为其小基因组和大量染色体。因此，在本研究中，使用PloidyNGS这个工具来计算在基因组序列每个位置支持不同等位基因的读取数，并使用荧光原位杂交与酪酰胺信号放大（TSA-FISH）来阐明G. lemaneiformis。此外，流式细胞仪（FCM）用于估计不同体细胞的倍性。PloidyNGS结果表明配子体中的大多数等位基因是单态的，而TSA-FISH结果表明，当通过单拷贝基因探针杂交时，配子体核中观察到一个杂交信号，四孢子体核中观察到两个杂交信号。这些结果证实，Lemaneiformis G是配子体世代中的单倍体和孢子体世代中的二倍体。此外，FCM结果表明，龙须菜不是一个endopolyploid。根据以前的研究，我们假设核数对于该物种的细胞分化和功能很重要。我们也建议Lemaneiformis G.从古多倍体进化而来，其基因组已经二倍体化，基因组加倍的痕迹不再明显。因此，这项研究为进一步研究红藻的进化和基因组提供了重要的证据。