背景回顾：Gynandropsis gynandra (Cleomaceae) is a cosmopolitan leafy vegetable and medicinal plant, which has also been used as a model to study C4 photosynthesis due to its evolutionary proximity to C3 Arabidopsis (Arabidopsis thaliana). 

主要研究：Here, we present the genome sequence of G. gynandra, anchored onto 17 main pseudo-molecules with a total length of 740 Mb, an N50 of 42 Mb and 30,933 well-supported gene models. The G. gynandra genome and previously released genomes of C3 relatives in the Cleomaceae and Brassicaceae make an excellent model for studying the role of genome evolution in the transition from C3 to C4 photosynthesis. 

结果1-全基因组复制事件：Our analyses revealed that G. gynandra and its C3 relative Tarenaya hassleriana shared a whole-genome duplication event (Gg-α), then an addition of a third genome (Th-α,  + 1x) took place in T. hassleriana but not in G. gynandra. 

结果2-C4光合相关基因家族：Analysis of syntenic copy number of C4 photosynthesis-related gene families indicates that G. gynandra generally retained more duplicated copies of these genes than C3 T. hassleriana, and also that the G. gynandra C4 genes might have been under positive selection pressure. 

结果3-基因复制：Both whole-genome and single-gene duplication were found to contribute to the expansion of the aforementioned gene families in G. gynandra. 

结论：Collectively, this study enhances our understanding of the polyploidy history, gene duplication and retention, as well as their impact on the evolution of C4 photosynthesis in Cleomaceae.

山柑科白花菜（Gynandropsis gynandra，又名羊角菜，一年生C4草本）是全球性的绿叶类蔬菜和药用植物，因其与C3植物拟南芥在系统发育上分属于姊妹科的关系，被广泛用作C4光合作用研究的模式植物。本文中，作者报道了白花菜的基因组，大小约为740Mb，挂载到了17条拟染色体上，包含约30933个蛋白编码基因。本文所报道的白花菜基因组，结合先前已经报道过的山柑科和十字花科的C3植物基因组，为研究C3到C4光合转变过程中的基因组演化提供了理想模型。作者通过研究发现，白花菜与其C3近缘种醉蝶花（山柑科醉蝶花属一年生C3草本）共享了一次全基因组复制事件（Gg-α），接着醉蝶花中又多复制了一套染色体（Th-α,  + 1x），但是白菜花却没有。通过对C4光合作用相关基因家族的共线性拷贝数变异分析，发现相比于C3植物醉蝶花，白花菜保留了更多的基因复制拷贝，并且白花菜中的C4基因可能处于正选择压下。全基因组复制和单基因拷贝都作用于白花菜中C4光合作用相关基因家族的扩张。综上，本文的研究拓展了我们对于山柑科植物多倍化历史、基因复制和保留以及其对于C4光合作用演化的影响。

** M Eric Schranz **