RALFs (Rapid Alkalinization Factors, based on historical observations that they induce alkalization of the extracellular space) are signaling peptides with diverse roles. RALF4 is required for pollen tube growth and guidance through its interactions with CrRLK1Ls and leucine-rich extension (LRX) proteins. Moussu, Broyart et al. characterized the complex formed between RALF4 and homodimers of the LRX2 or LRX8. RALF4 has conserved Cys residues and binds to the LRR core of the LRXs in the folded conformation. The RALF binding pocket is highly conserved among the known LRX family members. The authors also examined binding of RALF4 with pollen-expressed CrRLK1Ls and found that these interactions occur with very different affinities and modes of binding. The authors conclude, “ these findings suggest that RALFs have the capacity to instruct different signaling proteins to coordinate cell wall remodeling during pollen tube growth.” (Summary by Mary Williams) bioRxiv 10.1101/695874
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