Receptor-like protein kinase that mediates the female control of male gamete delivery during fertilization, including growth cessation of compatible pollen tubes ensuring a reproductive isolation barriers, by regulating MLO7 subcellular polarization upon pollen tube perception in the female gametophyte synergids. Required for cell elongation during vegetative growth, mostly in a brassinosteroids- (BR-) independent manner. Acts as an upstream regulator for the Rac/Rop-signaling pathway that controls ROS-mediated root hair development. Seems to regulate a cross-talk between brassinosteroids and ethylene signaling pathways during hypocotyl elongation. Negative regulator of brassinosteroid response in light-grown hypocotyls, but required for brassinosteroid response in etiolated seedlings. Mediates sensitivity to powdery mildew (e.g. Golovinomyces orontii). Positive regulator of auxin-promoted growth that represses the abscisic acid (ABA) signaling via the activation of ABI2 phosphatase. Required for RALF1-mediated extracellular alkalinization in a signaling pathway preventing cell expansion. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts with ROPGEF1 (PubMed:20876100). Interacts with RALF1; triggering phosphorylation status and subsequent activation (PubMed:24458638). Interacts with LRE and LLG1 (PubMed:26052747). Accumulates asymmetrically in the female gametophyte synergid membrane at the filiform apparatus. Expressed in leaves, buds, flowers, siliques, young ovules primordia, and young anthers with immature pollen, but not detected in mature pollen. Highest expression in the synergid cells of the female gametophyte. Detected in floral apices, young ovule primordia, and young anthers with immature pollen, but not in older anthers with mature pollen. After fertilization, expressed in globular embryos. By brassinosteroids (BR). Autophosphorylated. Phosphorylated at Ser-858, Ser-871 and Ser-874 upon activation by RALF1. Embryonic lethality due to impaired fertilization. The pollen tube fails to arrest and continues to grow inside the female gametophyte. Disturbed MLO7 relocalization to the filiform apparatus upon pollen tube arrival at the micropyle. Severe cell elongation defect in RNAi mutants with decreased FER expression. In fer-2 seedlings, altered responsiveness to brassinosteroids but increased ethylene response during the regulation of hypocotyl elongation. Increased resistance to powdery mildew (e.g. Golovinomyces orontii). Abscisic acid- (ABA)- hypersensitive response. Longer roots. Insensitivity to RALF1-mediated root-growth inbibition but hypersensitive to cation lithium inhibition. Female paralog of ANXUR, a male factor expressed in pollen tube that controls release of the sperm cell. Named after the Etruscan goddess of fertility Feronia. 'Sirene' means siren in French. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family. Sequencing errors.