Rapid alkalinization factor 22 has a structural and signalling role in root hair cell wall assembly
Résumé
Pressurized cells with strong walls make up the hydrostatic skeleton of
plants. Assembly and expansion of such stressed walls depend on a family of
secreted RAPID ALKALINIZATION FACTOR (RALF) peptides, which bind both
a membrane receptor complex and wall-localized LEUCINE-RICH REPEAT
EXTENSIN (LRXs) in a mutually exclusive way. Here we show that, in root hairs,
the RALF22 peptide has a dual structural and signalling role in cell expansion.
Together with LRX1, it directs the compaction of charged pectin polymers at
the root hair tip into periodic circumferential rings. Free RALF22 induces the
formation of a complex with LORELEI-LIKE-GPI-ANCHORED PROTEIN 1 and
FERONIA, triggering adaptive cellular responses. These findings show how
a peptide simultaneously functions as a structural component organizing
cell wall architecture and as a feedback signalling molecule that regulates
this process depending on its interaction partners. This mechanism may also
underlie wall assembly and expansion in other plant cell types
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