背景回顾：Symbiotic nitrogen fixation by Rhizobium bacteria in the cells of legume root nodules alleviates the need for nitrogen fertilizers. Nitrogen fixation requires the endosymbionts to differentiate into bacteroidswhich can be reversible or terminal. The latter is controlled by the plant, it is more beneficial and has evolved in multiple clades of the Leguminosae family. The plant effectors of terminal differentiation in inverted repeat-lacking clade legumes (IRLC) are nodule-specific cysteine-rich (NCR) peptides, which are absent in legumes such as soybean where there is no terminal differentiation of rhizobia. 

主要研究：It was assumed that NCRs co-evolved with specific transcription factors, but our work demonstrates that expression of NCR genes does not require NCR-specific transcription factors. 

结果1-NCR169基因功能：Introduction of the Medicago truncatula NCR169 gene under its own promoter into soybean roots resulted in its nodule-specific expression, leading to bacteroid changes associated with terminal differentiation. 

结果2-AHL-NCR169：We identified two AT-Hook Motif Nuclear Localized (AHL) transcription factors from both M. truncatula and soybean nodules that bound to AT-rich sequences in the NCR169 promoter inducing its expression. 

结果3-AHL调控更多的NCRs：Whereas mutation of NCR169 arrested bacteroid development at a late stage, the absence of MtAHL1 or MtAHL2completely blocked bacteroid differentiation indicating that they also regulate other NCRgenes required for the development of nitrogen-fixing nodules. 

结论：Regulation of NCRs by orthologous transcription factors in non-IRLC legumes opens up the possibility of increasing the efficiency of nitrogen fixation in legumes lacking NCRs.

 摘 要 

豆类植物根瘤细胞中根瘤菌介导的共生固氮减少了其对于氮肥的需求。氮固定需要内共生体分化形成具有强固氮能力的类菌体，而这一过程可以是可逆的，也可以是终点反应。后者受到植物的控制，其更加有益，并且在多个豆科植物家族中独立演化。反向重复序列缺失的豆科植物（IRLC）中末端分化的植物效应子是根瘤特异性的富含半胱氨酸（NCR）多肽，其在没有根瘤菌最终分化的豆科植物（如大豆）中不存在。据推测，NCRs基因与特定转录因子共演化，但是作者的工作表明NCR基因的表达并不需要NCR特异性的转录因子。利用苜蓿NCR169基因自身的启动子驱动自身，将其转入大豆根中会表现出根瘤特异性的表达模式，导致与末端分化相关的类菌体改变。作者在苜蓿和大豆的根瘤中分别都鉴定到了两个AHL转录因子，其能够结合到NCR169启动子的AT-rich序列上并诱导该基因的表达。鉴于NCR169基因的功能缺失突变会导致类菌体发育后期的停滞，同时MtAHL1或者MtAHL2的缺失会完全阻碍类菌体分化，说明MtAHL1/2还能够调控其他作用于固氮根瘤发育的NCR基因。在非IRLC豆科植物中通过AHLs转录因子调控NCRs，为提高缺乏NCRs豆科植物的固氮效率提供了可能性。