Arabidopsis RopGEF4 and RopGEF10 are important for FERONIA-mediated developmental but not environmental regulation of root hair growth.

We investigated a genetic pathway in root hair development in Arabidopsis thaliana, involving the receptor-like kinase FERONIA (FER), two guanine nucleotide exchange factors for ROPs (RopGEF4 and RopGEF10), and the small GTPase Rho of plants (ROPs). Loss- and gain-of-function analyses demonstrated distinct roles of RopGEF4 and RopGEF10 such that RopGEF4 is only important for root hair elongation, while RopGEF10 mainly contributes to root hair initiation. Domain dissection by truncation and domain-swapping experiments indicated that their functional distinctions were mainly contributed by the noncatalytic domains. Using fluorescent ratio imaging, we showed that functional loss of RopGEF4 and RopGEF10 additively reduced reactive oxygen species (ROS) production. Bimolecular fluorescence complementation experiments demonstrated that RopGEF4 and RopGEF10 had the same interaction specificity as ROPs, suggesting common downstream components. We further showed that the promoting effects of environmental cues such as exogenous auxin and phosphate limitation on root hair development depended on FER. However, although functional loss of RopGEF4 and RopGEF10 largely abolished FER-induced ROS production, it did not compromise the responses to FER-mediated environmental cues on root hair development. Our results demonstrated that RopGEF4 and RopGEF10 are genetic components in FER-mediated, developmentally (but not environmentally) regulated, root hair growth.