Small molecule RHP1 promotes root hair tip growth by acting upstream of the RHD6-RSL4-dependent transcriptional pathway and ROP signaling in plants

Root hairs are single-cell projections in the root epidermis. The presence of root hairs greatly expands the root surface, which facilitates soil anchorage and the absorption of water and nutrients. Root hairs are also the ideal system to study the mechanism of polar growth. Previous research has identified many important factors that control different stages of root hair development. Using a chemical genetics screen, in this study we report the identification of a steroid molecule, RHP1, which promotes root hair growth at nanomolar concentrations without obvious change of other developmental processes. We further demonstrate that RHP1 specifically affects tip growth with no significant influence on cell fate or planar polarity. We also show that RHP1 promotes root hair tip growth via acting upstream of the RHD6-RSL4-dependent transcriptional pathway and ROP GTPase-guided local signaling. Finally, we demonstrate that RHP1 exhibits a wide range of effects on different plant species in both monocots and dicots. This study of RHP1 will not only help to dissect the mechanism of root hair tip growth but also provide a new tool to modify root hair growth in different plant species.