MLO ‐mediated Ca ²⁺ influx regulates root hair tip growth in Arabidopsis

Root hair tip‐growth involves coordinated Ca ²⁺ and ROS signaling to promote growth while maintaining tip integrity. MILDEW RESISTANCE LOCUS‐O (MLO) proteins act downstream of FERONIA (FER) receptor‐like kinases in pollen tubes and synergids to regulate calcium dynamics. This study uses a constitutively active MLO (faNTA) to identify a new role for the FER/MLO signaling module in regulating [Ca ²⁺ ] _cyt oscillations in growing root hairs.

faNTA was used as a tool to manipulate Ca ²⁺ influx in fer mutants. Light sheet fluorescence imaging was used to image the reporter R‐GECO1 to observe [Ca ²⁺ ] _cyt dynamics during root hair elongation in various genotypes.

We show that faNTA is sufficient to restore normal root hair development, [Ca ²⁺ ] _cyt oscillations, and ROS levels to fer‐4 . MLO15 was identified as a regulator of root hair tip growth based on disrupted root hair growth and [Ca ²⁺ ] _cyt signatures in mlo15‐4 . We also link the FER/MLO module to ROS accumulation by showing that faNTA is sufficient to restore ROS levels in fer‐4 root hairs, but is unable to complement the burst root hairs of rbohc.

We propose that MLOs act downstream of FER to mediate Ca ²⁺ influx and promote ROS production to regulate root hair tip growth.