Arabidopsis RopGEF4and RopGEF10Mediate Root Hair Growth

Root hairs are cylindrical outgrowths from root epidermal cells, playing important rolesin water uptake, nutrient acquisition and environmental sensing, essential for the success ofvascular plants.Root hair development provides an excellent system to study fundamental biologicalquestions such as cell fate determination, symmetry breaking, and tip growth, which areexemplified by the three steps leading to a root hair. Extensive genetic studies in the pastdecade identified key genes whose mutations resulted in defects in root hair development,more root hair mutants: gl2, ttg, wer, pom1; less root hair mutants: cpc, rhl1, rhl2, rhl3;branched root hair mutants: cow1, cen1, cen2, cen3, rhd1, rhd3; wavy root hair mutants: rhd4,arp2, agd1.An emerging genetic network controlling root hair development reveals the central roleof the small GTPases Rho of plants (ROPs). By switching between the GDP-bound “off” stateand the GTP-bound “on” state, ROPs dynamically regulate diverse cellular activities such asactin microfilament organization, ROS production and Ca2+gradients, all of which playessential roles in root hair development.This paper used Arabidopsis thaliana as materials to explore the existed signalmechanism FER-GEFs-ROP-ROS in the followed five aspects:(1) Although GEF4and GEF10belonged to the same family and were both expressed inroot hairs, their respective mutants showed different effects in root hair development.(2) In order to magnify the difference between GEF4and GEF10, GEF4and GEF10were drived with a root hair-specific highly expressed promoter: EXPA7. GEF4gain offunction showed slightly wavy root hairs. GEF10gain of function showed branched roothairs.(3) Compared the second structure of GEF4and GEF10, we found that C-termini was lost for GEF4. Domain swapped results support that N-termini was essential for GEF4andC-termini was essential for GEF10.(4) FER gain of function resulted in enhanced ROS production, was significantlyreduced in gef4gef10. We provided evidence that FER was upstream regulator of GEF4andGEF10in ROS production.(5) fer-4showed no response to exogenous auxin induction and phosphate stress,gef4gef10show hypersensitive response to auxin induction and phosphate stress. FER senseddevelopmental and environmental cues, regulated root hair development and growth, wasindependent of GEF4and GEF10.