背景回顾：Ice plant (Mesembryanthemum crystallinum), a member of the Aizoaceae family, is a typical halophyte crop and a model plant for studying the mechanism of transition from C3 photosynthesis to crassulacean acid metabolism (CAM). 

主要研究：Here, we report a high-quality chromosome-level ice plant genome sequence.  

结果1-基因组特征：This 98.05% genome sequence is anchored to nine chromosomes, with a total length of 377.97 Mb and an N50 scaffold of 40.45 Mb. Almost half of the genome (48.04%) is composed of repetitive sequences, and 24,234 genes have been annotated. 

结果2-基因组演化：Subsequent to the ancient whole-genome triplication (WGT) that occurred in eudicots, there has been no recent whole-genome duplication (WGD) or WGT in ice plants. However, we detected a novel WGT event that occurred in the same order in Simmondsia chinensis, which was previously overlooked. Our findings revealed that ice plants have undergone chromosome rearrangements and gene removal during evolution. 

结果3-CAM途径：Combined with transcriptome and comparative genomic data and expression verification, we identified several key genes involved in the CAM pathway and constructed a comprehensive network. 

结论：As the first genome of the Aizoaceae family to be released, this report will provide a rich data resource for comparative and functional genomic studies of Aizoaceae, especially for studies on salt tolerance and C3-to-CAM transitions to improve crop yield and resistance.

 摘 要 

冰叶日中花（Mesembryanthemum crystallinum）属于番杏科植物，一个典型的盐生作物以及用于研究从C3光合向景天酸代谢CAM转换的模式植物。本文中，作者报道了一个高质量的染色体水平冰叶日中花基因组。98.05%的基因组序列能够被挂载到9条染色体上，总长为377.97 Mb，scaffold N50长度为40.45 Mb。48.04%的基因组属于重复序列，几乎占了基因组的一半，共包含24234个基因。在真双子叶植物共同祖先发生了古三倍化之后，冰叶日中花基因组中未能检测到后续发生过全基因组二倍化或三倍化事件。但是，作者在同一目下的霍霍巴中检测到了一次新的全基因组三倍化事件，而这在之前的研究中一直被忽略了。另外，作者发现冰叶日中花在演化过程中经历了染色体重排和基因丢失。结合转录组、比较基因组学以及表达验证数据，作者鉴定了参与CAM途径的关键基因，共同构建了一个综合网络。作为番杏科第一个报道基因组的物种，本文的研究为番杏科的比较基因组和功能基因组研究提供了一个参考基因组，同时为耐盐机制和C3向CAM转变研究提供了遗传资源，用于未来育种项目中的作物产量和抗性提升。

p.s. 适宜条件下，冰叶日中花通过C3途径进行光合作用，白天气孔处于开放状态，CO2与C5结合进入卡尔文循环，卡尔文循环发生的场所是叶绿体基质；长期在高温、缺水、高盐等逆境胁迫下，冰叶日中花进行CAM途径，白天气孔关闭（减少水分损失），CO2部分来源于苹果酸分解，还有部分来自于细胞呼吸。

 宋小明