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.
Bibliographical noteFunding Information:
This study was supported by grants from the Next-Generation BioGreen 21 Program (PJ013220), RDA, Republic of Korea, and Mid-career Researcher Program (2016R1A2B4015201) and Basic Research Laboratory (2017R1A4A1015620) through the National Research Foundation of Korea, funded by the Ministry of Education, Science, and Technology of Korea to J.K.
© 2018 The Authors The Plant Journal © 2018 John Wiley & Sons Ltd
- Arabidopsis thaliana
- feedback regulation
- lateral root development
- protein–protein interaction
- transcriptional regulation
ASJC Scopus subject areas
- Plant Science
- Cell Biology