背景回顾：Rhododendrons are woody plants, famous throughout the world as having high horticultural value. 

提出问题：However, many wild species are currently threatened with extinction.

主要研究：Here, we report for the first time a high-quality, chromosome-level genome of Rhododendron griersonianum, which has contributed to approximately 10% of all horticultural rhododendron varieties but which in its wild form has been evaluated as critically endangered. 

结果1-组装+注释：The final genome assembly, which has a contig N50 size of approximately 34 M and a total length of 677 M, is the highest-quality genome sequenced within the genus to date, in part due to its low heterozygosity (0.18%). Identified repeats constitute approximately 57% of the genome, and 38 280 protein-coding genes were predicted with high support. 

结果2-群体：We further resequenced 31 individuals of R. griersonianum as well as 30 individuals of its widespread relative R. delavayi, and performed additional conservation genomic analysis. 

结果2.1-遗传多样性：The results showed that R. griersonianum had lower genetic diversity (θ = 2.58e−3; π = 1.94e−3) when compared not only to R. delavayi (θ = 11.61e−3, π = 12.97e−3), but also to most other woody plants. 

结果2.2-遗传瓶颈：Furthermore, three severe genetic bottlenecks were detected using both the Stairway plot and fastsimcoal2 analysis, which are thought to have occurred in the late Middle Pleistocene and the Last Glacial Maximum (LGM) period. After these bottlenecks, R. griersonianum recovered and maintained a constant effective population size (>25 000) until now. 

结果2.3-有害突变：Intriguingly, R. griersonianum has accumulated significantly more deleterious mutations in the homozygous state than R. delavayi, and several deleterious mutations (e.g., in genes involved in the response to heat stress) are likely to have harmed the adaptation of this plant to its surroundings. 

结论：This high-quality, chromosome-level genome and the population genomic analysis of the critically endangered R. griersonianum will provide an invaluable resource as well as insights for future study in this species to facilitate conservation and in the genus Rhododendron in general.

 摘 要 

杜鹃是木本植物，具有极高的观赏价值，是全球著名的园艺植物。但是，许多野生的杜鹃目前正濒临灭绝。本文中，作者首次报道了一个高质量的、染色体级别的朱红大杜鹃（Rhododendron griersonianum）基因组，该品种的杜鹃约占整个园艺杜鹃品种的10%，但其野生资源被评为极度濒危。杜鹃基因组大小677Mb，contig N50长34Mb，是该属中基因组组装质量最高的物种，可能部分原因是该物种的杂合度非常低，仅为0.18%。重复序列约占杜鹃基因组的57%，共注释到38280个蛋白编码基因。作者进一步对31份朱红大杜鹃材料和30份其广泛分布的近缘种马缨杜鹃（R. delavayi）进行了重测序，结果发现朱红大杜鹃的遗传多样性不仅要比马缨杜鹃低，而且相比于其他的木本植物都要低。此外，作者检测到了三次严重的遗传瓶颈，可能发生在中更新世晚期和末次盛冰期。在这些遗传瓶颈发生之后，朱红大杜鹃种群恢复并至今保持了较为稳定的有效群体大小（超过25000）。有趣的是，相比于马缨杜鹃，朱红大杜鹃以纯合子的方式积累了更多的有害突变，其中在热胁迫响应基因等重要基因上的有害突变很有可能降低了该物种对于周边环境的适应性。本文所报道的高质量朱红大杜鹃基因组和群体基因组分析为这一濒危植物的保护提供了宝贵的遗传资源。