Arabidopsis <scp>ADF8</scp> and <scp>ADF11</scp> contribute to root hair growth to respond to hormone and environmental signals

Root hairs play important roles in the acquisition of nutrients and water, in soil anchorage, and in the interaction with soil-living biota. Root hair growth requires the dynamic actin filament (F-actin) meshwork and responds to phytohormones and environmental cues. However, how hormonal signals directly regulate F-actin meshwork dynamics to modulate root hair growth remains unclear. Here, we report that Arabidopsis actin-depolymerizing factor ADF8 and ADF11, preferentially expressed in root hairs, are transcriptionally induced by auxin and ethylene. Root hair of adf8;11 exhibits reduced sensitivity to auxin and ethylene, accompanied by failure to maintain the F-actin meshwork at the root hair tip. Furthermore, we found that ADF8/11 participate in root hair elongation induced by low-phosphate and low-nitrogen conditions. Notably, our study demonstrates that the expression of ADF8/11 is regulated by transcription factor RSL4, auxin-responsive ARFs, and ethylene-responsive EIN3, indicating that hormonal signals influence F-actin dynamics by modulating ADF8/11 transcription. In summary, our research demonstrates that ADF8/11 are key factors for root hairs to respond to environmental-hormonal signals and establishes a direct link between hormonal signaling and F-actin dynamics in root hairs.