背景-1：Sucrose and auxin are well-known determinants of root system architecture (RSA). However, the factors that connect the signaling pathways evoked by these two critical factors during root development are poorly understood. 

主要发现：In this study, we report the role of MEDIATOR SUBUNIT17 (MED17) in RSA and its involvement in the transcriptional integration of sugar and auxin signaling pathways in Arabidopsis (Arabidopsis thaliana). 

背景-2：Sucrose regulates root meristem activation through the TARGET OF RAPAMYCIN-E2 PROMOTER BINDING FACTOR A TOR-E2FA pathway, and auxin regulates lateral root (LR) development through AUXIN RESPONSE FACTOR-LATERAL ORGAN BOUNDARIES DOMAIN ARF-LBDs. Both sucrose and auxin play a vital role during primary and LR development. However, there is no clarity on how sucrose is involved in the ARF-dependent regulation of auxin-responsive genes. 

主要发现：This study establishes MED17 as a nodal point to connect sucrose and auxin signaling. 

结果1-MED17表达受到蔗糖诱导：Transcription of MED17 was induced by sucrose in an E2FA/B-dependent manner. 

结果2-MED17-E2FA/B互作-ARF7：Moreover, E2FA/B interacted with MED17, which can aid in the recruitment of the Mediator complex on the target promoters. Interestingly, E2FA/B and MED17 also occupied the promoter of ARF7, but not ARF19, leading to ARF7 expression, which then activates auxin signaling and thus initiates LR development. 

结论3-MED17-细胞周期基因：MED17 also activated cell division in the root meristem by occupying the promoters of cell-cycle genes, thus regulating their transcription. 

​结论：Thus, MED17 plays an important role in relaying the transcriptional signal from sucrose to auxin-responsive and cell-cycle genes to regulate primary and lateral root development, highlighting the role of the Mediator as the transcriptional processor for optimal root system architecture in Arabidopsis.

蔗糖和生长素是决定根系统结构的关键因子。但是，在根发育过程中同时关联这两个因子的信号转导途径仍不清楚。本文中，作者报道了拟南芥MED17在根系统结构中的作用，以及其参与转录整合蔗糖和生长素信号转导途径的功能。蔗糖通过TOR-E2F1-E2FA途径调控根分生组织激活，而生长素通过ARF-LBDs调控侧根发育。蔗糖和生长素在主根和侧根的发育过程中都发挥了关键作用。但是，目前还不清楚蔗糖是如何参与依赖于ARF的生长素响应基因调控。本文发现MED17作为一个节点，连接蔗糖和生长素信号转导。MED17的转录受到蔗糖的诱导，并且该诱导表达依赖于E2FA/B。此外，E2FA/B与MED17能够发生互作，有助于将Mediator复合物招募至靶基因的启动子上。有趣的是，E2FA/B和MED17还会占据ARF7基因的启动子，但是并不能够占据的ARF19启动子，从而促进ARF7的表达，进而激活生长素信号转导，起始侧根的发育。MED17还能够通过占据细胞周期基因的启动子，调控这些基因的转录，从而激活根分生组织中的细胞分裂。因此，MED17在转接从蔗糖到生长素响应和细胞周期基因的转录信号中发挥重要作用，从而调控主根和侧根的发育，突出了Mediator作为转录处理器作用于根系统结构的功能。

** Jitendra Kumar Thakur **