ENHANCED GRAVITROPISM 2 调控大麦和小麦的根部生长角度
根系生长角决定了根系如何向重力方向生长，是根系结构最重要的决定因素之一。它控制着作物的吸水能力、养分利用效率、抗逆性和产量。我们证明，与野生型相比，大麦egt2（ENHANCED GRAVITROPISM 2，增强的向重力性2）突变体的种子根和侧根的根系生长更为陡峭，并且对重力的响应性更高。
我们通过大量分离分析和全基因组测序相结合的方法克隆了EGT2基因。随后由一个独立的CRISPR/Cas9突变等位基因进行的验证实验表明，egt2编码一个含有蛋白质的STERILE ALPHA MOTIF 结构域。
原位杂交实验表明EGT2从根冠到延伸区均有表达。
亚细胞定位实验表明EGT2定位于细胞核和细胞质。
我们通过敲除四倍体硬粒小麦A和B基因组中的EGT2同源序列，证明了EGT2在大麦和小麦根系生长角调控中的进化保守性作用。
通过结合激光捕获显微切割和RNA-seq，我们观察到7个expansin基因在延伸区转录下调。这与EGT2在根的这个区域中的作用是一致的，在这个区域，重力感应的作用是通过细胞的差异伸长来实现的。
我们的研究结果表明，EGT2是大麦和小麦根系生长角的一个进化保守的调节因子，可能是基于根系的作物改良策略的一个有价值的目标。
The root growth angle defines how roots grow towards 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. 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. We cloned the EGT2 gene by a combination of bulked segregant analysis and whole genome sequencing. Subsequent validation experiments by an independent CRISPR/Cas9 mutant allele demonstrated that egt2 encodes a STERILE ALPHA MOTIF domain containing protein. In situ hybridization experiments illustrated that EGT2 is expressed from the root cap to the elongation zone. Subcellular localization experiments revealed that EGT2 localizes to the nucleus and cytoplasm. 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. By combining laser capture microdissection with RNA-seq, we observed that seven expansin genes were transcriptionally downregulated 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. 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.
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