Identification of mebendazole as an ethylene signaling activator reveals a role of ethylene signaling in the regulation of lateral root angles.

The lateral root angle or gravitropic set-point angle (GSA) is an important trait for root system architecture (RSA) that determines the radial expansion of the root system. The GSA therefore plays a crucial role for the ability of plants to access nutrients and water in the soil. Only a few regulatory pathways and mechanisms that determine GSA are known. These mostly relate to auxin and cytokinin pathways. Here, we report the identification of a small molecule, mebendazole (MBZ), that modulates GSA in Arabidopsis thaliana roots and acts via the activation of ethylene signaling. MBZ directly acts on the serine/threonine protein kinase CTR1, which is a negative regulator of ethylene signaling. Our study not only shows that the ethylene signaling pathway is essential for GSA regulation but also identifies a small molecular modulator of RSA that acts downstream of ethylene receptors and that directly activates ethylene signaling. [Display omitted] • MBZ increases lateral root angle • MBZ regulates lateral root angle by activating ethylene signaling • MBZ inhibits CTR1 kinase activity • The ethylene pathway is involved in lateral root angle regulation He et al. identify a small molecule that regulates lateral root angle. They show that the compound increases lateral root angle by inhibiting CTR1 kinase activity, which in turn activates ethylene signaling. Therefore, they show that the ethylene pathway is involved in lateral root angle regulation. [ABSTRACT FROM AUTHOR]