LBD18 uses a dual mode of a positive feedback loop to regulate ARF expression and transcriptional activity in Arabidopsis

First author: Shashank K. Pandey; Affiliations: Chonnam National University (全南国立大学): Gwangju, Korea

Corresponding author: Jungmook Kim

A hierarchy of transcriptional regulators controlling lateral root formation in Arabidopsis thaliana has been identified, including the AUXIN RESPONSE FACTOR 7 (ARF7)/ARF19‐LATERAL ORGAN BOUNDARIES DOMAIN 16 (LBD16)/LBD18 transcriptional network; however, their feedback regulation mechanisms are not known. Here we show that LBD18 controls ARF activity using the dual mode of a positive feedback loop. We showed that ARF7 and ARF19 directly bind AuxRE in the LBD18 promoter. A variety of molecular and biochemical experiments demonstrated that LBD18 binds a specific DNA motif in the ARF19 promoter to regulate its expression in vivo as well as in vitro. LBD18 interacts with ARFs including ARF7 and ARF19 via the Phox and Bem1 domain of ARF to enhance the transcriptional activity of ARF7 on AuxRE, and competes with auxin/indole‐3‐acetic acid (IAA) repressors for ARF binding, overriding the negative feedback loop exerted by Aux/IAA repressors. Taken together, these results show that LBD18 and ARFs form a double positive feedback loop, and that LBD18 uses the dual mode of a positive feedback loop by binding directly to the ARF19 promoter and through the protein–protein interactions with ARF7 and ARF19. This novel mechanism of feedback loops may constitute a robust feedback mechanism that ensures continued lateral root growth in response to auxin in Arabidopsis.

拟南芥中有关侧根形成的转录调控网络已经被鉴定，主要包括生长素响应因子ARF7/ARF19与侧生器官边界结构域LBD16/LBD18组成的转录调控网络，然而关于这两者之间的反馈调节的机制还不清楚。本文的研究揭示了LBD18通过双重的正向反馈回路控制ARF的活性。作者的研究显示ARF7和ARF19能够直接结合到LBD18基因启动子区的AuxRE。另外，体内和体外的分子和生化试验均显示LBD18能够结合到ARF19基因启动子区的一个特定DNA基序，并调控ARF19基因的表达。LBD18能够通过Phox和Bem1结构域与ARF7和ARF19两个ARF蛋白互作，增加ARF7在AuxRE上的转录活性，并与生长素IAA抑制子竞争跟ARF的结合，从而减弱Aux/IAA抑制子对于ARF蛋白的负反馈回路。综上，本文的结果说明LBD18与ARF基因能够形成双正向反馈回路，LBD18通过直接结合到ARF19基因的启动子及与ARF7和ARF19的蛋白质互作形成了一个双元正向反馈回路。这种新的反馈回路的发现可能对于拟南芥响应生长素表现出的持续性侧根生长提供了合理的反馈调节机制。

doi: https://doi.org/10.1111/tpj.13945

Journal: the plant journal

First Published: 22 April, 2018

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