ABSTRACT
In plants, root hairs undergo a highly-polarized form of cell expansion called tip-growth, in which cell expansion is restricted to the root hair apex. In order to characterize cellular components playing a role in this specialized form of cellular expansion we screened for conditional temperature sensitive (ts) mutants by EMS mutagenesis. Here we describe one of these mutants, fer-ts (feronia-temperature sensitive). Mutant fer-ts seedlings grew normally at permissive temperatures (20°C), but failed to form root hairs at non-permissive temperatures (30°C). Map based-cloning and whole genome sequencing revealed that fer-ts resulted from a G41S substitution in the extracellular domain of FERONIA (FER). A functional fluorescent fusion of FER containing the fer-ts mutation maintained a plasma membrane localization at both permissive and non-permissive temperatures, but that the fer-ts allele was subject to enhanced protein turnover at elevated temperatures. Mutant fer-ts seedlings were resistant to added RALF1 peptide at non-permissive temperatures, supporting a role for FER in perception of this peptide hormone. Additionally, at non-permissive temperatures fer-ts seedlings displayed altered ROS accumulation upon auxin treatment and phenocopied constitutive fer mutant responses to a variety of plant hormone treatments. Molecular modeling and sequence comparison with other CrRLK1L receptor family members revealed that the mutated glycine in fer-ts is highly conserved, but significantly removed from recently characterized RALF23 and LORELI-LIKE-GLYCOPROTEIN (LLG2) binding domains, perhaps suggesting that fer-ts phenotypes may not be directly due to loss of binding to RALF1 peptides.