Abstract
AtGRP3 is a glycine-rich protein from Arabidopsis thaliana shown to interact with the extracellular domain of the receptor-like kinase (RLK) AtWAK1. Based on previous functional data for AtWAK1, a model was proposed that AtGRP3 when bound to this RLK would negatively regulate its kinase activity, inhibiting cell expansion. Here, we review recent functional studies on AtGRP3 that corroborate this model and suggest that AtGRP3/AtWAK1 complex regulates also defense signaling pathways. On the other hand, we show new data on AtGRP3-overexpressing plants indicating that its role in aluminum signaling pathways, as previously observed for elicitor signaling, seems to be more complex than a simple negative regulator.