Several receptor-ligand pairs are now Int. J. Mol. Sci. 2017, 18, 1164 15 of 25 established such as SRK/SCR, LecRK-I.9/RGD-containing peptides or/and ATP, CERK1/chitin oligomers or peptidoglycan, and FER/RAFL. However, regarding the vast expansion of LecRLKs families in plants, ...