背景回顾：The root growth angle defines how roots grow toward the gravity vector and is among the most important determinants of root system architecture. It controls water uptake capacity, nutrient use efficiency, stress resilience, and, as a consequence, yield of crop plants. 

主要发现：We demonstrated that the egt2 (enhanced gravitropism 2) mutant of barley exhibits steeper root growth of seminal and lateral roots and an auxin-independent higher responsiveness to gravity compared to wild-type plants. 

结果1-克隆基因：We cloned the EGT2 gene by a combination of bulked-segregant analysis and whole genome sequencing. 

结果2-基因功能鉴定：Subsequent validation experiments by an independent CRISPR/Cas9 mutant allele demonstrated that egt2 encodes a STERILE ALPHA MOTIF domain–containing protein. 

结果3-表达模式：In situ hybridization experiments illustrated that EGT2 is expressed from the root cap to the elongation zone. 

结果4-演化保守性：We demonstrated the evolutionary conserved role of EGT2 in root growth angle control between barley and wheat by knocking out the EGT2 orthologs in the A and B genomes of tetraploid durum wheat. 

结果5-下游机制：By combining laser capture microdissection with RNA sequencing, we observed that seven expansin genes were transcriptionally down-regulated in the elongation zone. This is consistent with a role of EGT2 in this region of the root where the effect of gravity sensing is executed by differential cell elongation. 

结论：Our findings suggest that EGT2 is an evolutionary conserved regulator of root growth angle in barley and wheat that could be a valuable target for root-based crop improvement strategies in cereals.

 摘 要 

根生长角度定义了根如何朝着重力矢量的方向生长，是植物根系统决定因素中最为重要的一项。其控制了水分吸收能力、营养利用效率、胁迫的抵抗力以及最终作物的产量。本文中，作者鉴定了大麦的egt2突变体，该突变体与野生型相比，其初生根和侧根的生长角度更为朝向重力方向，并且存在一个独立于生长素的重力响应。作者通过BSA分析和全基因组重测序的方法，克隆到了该突变体的突变基因EGT2。接着，作者通过CRISPR/Cas9技术获得了EGT2基因功能缺失突变体，显示egt2编码一个含有SAM结构域的蛋白。原位杂交实验显示，EGT2在根冠到伸长区部分存在表达。作者通过敲除四倍体杜兰小麦A、B两套染色体上的EGT2直系同源基因，发现该基因在小麦和大麦中的功能十分保守。通过结合激光显微切割和RNA测序，作者发现有7个扩展蛋白（expansin）编码基因在根伸长区下调表达。该结果与在EGT2该区域的作用相一致，即通过差异性的细胞伸长来作用于重力的感应。本文的发现揭示了EGT2基因是一个大麦和小麦在演化上保守的基因，作用于根的重力响应，可以作为将来谷类作物根系统改良策略的候选基因。