Development of plant organs requires constant monitoring of endogenous and environmental cues for which plant cells have evolved a wide array of sensors. Among them, the receptor-like kinase (RLK) family is of particular relevance for plants due to its remarkable expansion during plant evolution. RLKs sense exogenous and endogenous signals, controlling a myriad of processes such as responses to hormones and pathogens. The Catharanthus roseus RLK 1-like (CrRLK1L) group of RLKs is known to control immunity and developmental processes like reproduction and cell expansion, and have been postulated to act as signalling hubs in which several cellular pathways converge. This is best exemplified by its most studied member, FERONIA (FER), a receptor of rapid alkalinisation factor (RALF) peptides and cell wall components, and a mediator of receptor complex assembly during pathogen perception.
In this project the Arabidopsis CrRLK1L receptor family was examined with the goal of identifying novel functions in plant development for uncharacterised or already characterised members. A CrRLK1L T-DNA mutant set was obtained and several higher order mutants generated to reveal defects masked by functional redundancy between related CrRLK1Ls. Initial screens identified roles for HERCULES RECEPTOR KINASE 1 (HERK1), HERK2 and THESEUS1 (THE1) in abscisic acid signalling during germination and a role during reproduction for HERK1 and its uncharacterised homolog ANJEA (ANJ). Further experiments confirmed the involvement of HERK1 and ANJ in controlling pollen tube reception in the ovule. HERK1 and ANJ were found to localise in the filiform apparatus of the synergid cells, to influence the relocalisation of NORTIA after pollen tube arrival and to physically associate with LORELEI. Additionally, the Arabidopsis RALF family was probed to identify regulators of reproduction, yielding the identification of peptides RALFL4 and RALFL19 as determinants of pollen tube growth stability
