Reliable identification of individual chromosomes in eukaryotic species is the foundation for comparative chromosome synteny and evolutionary studies. Unfortunately, chromosome identification has been a major challenge for plants with small chromosomes, such as the Citrus species. We developed oligonucleotide‐based chromosome painting probes for all nine chromosomes in Citrus maxima (Pummelo). We were able to identify all C. maxima chromosomes in the same metaphase cells using multiple rounds of sequential fluorescence in situ hybridization with the painting probes. We conducted comparative chromosome painting analysis in six different Citrus and related species. We found that each painting probe hybridized to only a single chromosome in all other five species, suggesting that the six species have maintained a complete chromosomal synteny after more than 9 million years of divergence. No interchromosomal rearrangement was identified in any species. These results support the hypothesis that karyotypes of woody species are more stable than herbaceous plants because woody plants need a longer period to fix chromosome structural variants in natural populations.

中文翻译：

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通过染色体特异性绘画揭示了柑橘属物种的染色体保守性。

可靠鉴定真核生物中的单个染色体是比较染色体同义和进化研究的基础。不幸的是，染色体鉴定已成为具有小染色体的植物（例如柑橘属植物）的主要挑战。我们为柑桔（Pummelo）的所有9条染色体开发了基于寡核苷酸的染色体绘画探针。我们能够使用绘画探针进行多轮顺序的荧光原位杂交，从而鉴定出同一中期细胞中的所有最大梭菌染色体。我们在六个不同的柑橘中进行了比较染色体绘画分析和相关物种。我们发现，每个绘画探针都与所有其他五个物种中的单个染色体杂交，这表明在超过900万年的差异之后，这六个物种保持了完整的染色体同构。在任何物种中均未发现染色体间重排。这些结果支持这样的假设：木本植物的核型比草本植物更稳定，因为木本植物需要更长的时间来固定自然种群中的染色体结构变异。