Arabidopsis COP1 suppresses root hair development by targeting type I ACS proteins for ubiquitination and degradation.

Root hairs (RHs) are an innovation of vascular plants whose development is coordinated by endogenous and environmental cues, such as ethylene and light conditions. However, the potential crosstalk between ethylene and light conditions in RH development is unclear. We report that Arabidopsis constitutive photomorphogenic 1 (COP1) integrates ethylene and light signaling to mediate RH development. Darkness suppresses RH development largely through COP1. COP1 inhibits both cell fate determination of trichoblast and tip growth of RHs based on pharmacological, genetic, and physiological analyses. Indeed, COP1 interacts with and catalyzes the ubiquitination of ACS2 and ACS6. COP1- or darkness-promoted proteasome-dependent degradation of ACS2/6 leads to a low ethylene level in underground tissues. The negative role of COP1 in RH development by downregulating ethylene signaling may be coordinated with the positive role of COP1 in hypocotyl elongation by upregulating ethylene signaling, providing an evolutionary advantage for seedling fitness. [Display omitted] • Root hairs respond to light or ethylene by increasing both density and length • Arabidopsis COP1, the light responsive factor, inhibits root hair development • COP1 catalyzes the ubiquitination of type I ACSs to reduce ethylene responses • Dark-induced 26S-proteasome-mediated degradation of type I ACSs largely depends on COP1 Yin et al. report that Arabidopsis constitutive photomorphogenic 1 (COP1), a light response factor, controls root hair development by catalyzing the ubiquitination of type I ACSs and degradation to inhibit ethylene biosynthesis. The negative role of COP1 in root hairs may coordinate with its positive role in hypocotyl elongation to promote seedling fitness. [ABSTRACT FROM AUTHOR]