Plant Mediator Lab, National Institute of Plant Genome Research, Aruna Asaf Ali Marg, New Delhi 110067, India.
Plant Transcription Regulation, International Centre for Genetic Engineering and Biotechnology, Aruna Asaf Ali Marg, New Delhi 110067, India.
Plant Physiol. 2023 May 31;192(2):1548-1568. doi: 10.1093/plphys/kiad129.
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. 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). 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. This study establishes MED17 as a nodal point to connect sucrose and auxin signaling. Transcription of MED17 was induced by sucrose in an E2FA/B-dependent manner. 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. MED17 also activated cell division in the root meristem by occupying the promoters of cell-cycle genes, thus regulating their transcription. 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.
蔗糖和生长素是众所周知的根系结构（RSA）决定因素。然而，在根系发育过程中，连接这两个关键因子引发的信号通路的因素还知之甚少。在这项研究中，我们报告了 MEDIATOR SUBUNIT17（MED17）在 RSA 中的作用及其在拟南芥（Arabidopsis thaliana）中糖和生长素信号通路转录整合中的参与。蔗糖通过 TARGET OF RAPAMYCIN-E2 PROMOTER BINDING FACTOR A（TOR-E2FA）途径调节根分生组织的激活，生长素通过 AUXIN RESPONSE FACTOR-LATERAL ORGAN BOUNDARIES DOMAIN（ARF-LBD）调节侧根（LR）发育。蔗糖和生长素在初级和 LR 发育中都起着至关重要的作用。然而，尚不清楚蔗糖如何参与 ARF 依赖的生长素响应基因的调节。本研究确立了 MED17 作为连接蔗糖和生长素信号的节点。MED17 的转录受蔗糖以 E2FA/B 依赖的方式诱导。此外，E2FA/B 与 MED17 相互作用，这有助于 Mediator 复合物在靶启动子上的募集。有趣的是，E2FA/B 和 MED17 也占据了 ARF7 的启动子，但不占据 ARF19 的启动子，导致 ARF7 表达，从而激活生长素信号，从而启动 LR 发育。MED17 还通过占据细胞周期基因的启动子，在根分生组织中激活细胞分裂，从而调节它们的转录。因此，MED17 在将转录信号从蔗糖传递到生长素响应和细胞周期基因中发挥重要作用，以调节初级和侧根发育，突出了 Mediator 作为拟南芥最佳根系结构转录处理器的作用。
