背景回顾：Clustered regularly interspaced short palindromic repeats and CRISPR-associated proteins (CRISPR-Cas) systems have been developed as important tools for plant genome engineering. 

主要发现：Here, we demonstrate that the hypercompact CasΦ nuclease is able to generate stably inherited gene edits in Arabidopsis, and that CasΦ guide RNAs can be expressed with either the Pol-III U6 promoter or a Pol-II promoter together with ribozyme mediated RNA processing. 

结果1-表观修饰对CasΦ编辑的影响：Using the Arabidopsis fwa epiallele, we show that CasΦ displays higher editing efficiency when the target locus is not DNA methylated, suggesting that CasΦ is sensitive to chromatin environment.  

结果2-CasΦ变体：Importantly, two CasΦ protein variants, vCasΦ and nCasΦ, both showed much higher editing efficiency relative to the wild-type CasΦ enzyme. Consistently, vCasΦ and nCasΦ yielded offspring plants with inherited edits at much higher rates compared to WTCasΦ. 

结果3-脱靶检测：Extensive genomic analysis of gene edited plants showed no off-target editing, suggesting that CasΦ is highly specific. 

结论：The hypercompact size, T-rich minimal protospacer adjacent motif (PAM), and wide range of working temperatures make CasΦ an excellent supplement to existing plant genome editing systems.

CasΦ-2介导的AtPDS3基因编辑

CRISPR-Cas系统已经被开发成为一个用作植物基因组编辑的重要工具。本文中，作者发现紧凑型CasΦ核酸酶能够在拟南芥中进行稳定遗传地基因编辑，并且CasΦ gRNA可以通过Pol-III U6或Pol-II启动子进行驱动表达，同时进行核酶介导的RNA加工。利用拟南芥fwa表观等位基因，作者发现CasΦ在靶位点不被DNA甲基化时表现出更高的编辑效率，说明CasΦ蛋白对于染色质环境敏感。重要的是，作者发现两个CasΦ蛋白变体vCasΦ和nCasΦ均要比野生型CasΦ蛋白表现出更高的编辑效率。与此一致，与野生型CasΦ蛋白相比，vCasΦ和nCasΦ产生的携带可遗传编辑的子代植株比率更高。对于基因编辑植株的基因组分析显示未鉴定到任何脱靶事件，表明CasΦ蛋白的高度特异性。本文所报道的高度紧凑型Cas蛋白，具备T-rich最小PAM序列以及广泛的工作温度环境，使得CasΦ蛋白成为现有植物基因编辑体系的一个最佳补充。

** Steven E. Jacobsen **