The SYP123-VAMP727 SNARE complex delivers secondary cell wall components for root hair shank hardening in Arabidopsis

The extended tubular shape of root hairs is established by tip growth and concomitant hardening. Here, we demonstrate that a syntaxin of plants (SYP)123-vesicle-associated membrane protein (VAMP)727-dependent secretion system delivers secondary cell wall components for hardening the subapical zone and shank of Arabidopsis (Arabidopsis thaliana) root hairs. We found increased SYP123 localization at the plasma membrane (PM) of the subapical and shank zones compared with the tip region in elongating root hairs. Inhibition of phosphatidylinositol (PtdIns)(3,5)P2 production impaired SYP123 localization at the PM and SYP123-mediated root hair shank hardening. Moreover, root hair elongation in the syp123 mutant was insensitive to a PtdIns(3,5)P2 synthesis inhibitor. SYP123 interacts with both VAMP721 and VAMP727. syp123 and vamp727 mutants exhibited reduced shank cell wall stiffness due to impaired secondary cell wall component deposition. Based on these results, we conclude that SYP123 is involved in VAMP721-mediated conventional secretion for root hair elongation as well as in VAMP727-mediated secretory functions for the delivery of secondary cell wall components to maintain root hair tubular morphology. The SYP123-VAMP727-mediated secretion pathway is involved in the transport of secondary cell wall components to the root hair shank for hardening in a PtdIns(3,5)P2-dependent manner.

Automated summary

This study demonstrates that the SYP123-VAMP727-dependent secretion pathway plays a crucial role in delivering secondary cell wall components for the hardening of the subapical zone and shank of Arabidopsis root hairs. The localization of SYP123 at the plasma membrane is dependent on the production of phosphatidylinositol (PtdIns)(3,5)P2, and this pathway is involved in maintaining the tubular morphology of root hairs by transporting secondary cell wall components. The study highlights the importance of SYP123-VAMP727-mediated secretion in root hair elongation and maintenance.