The functionally diverse expansins and the vesicular transport of canonical α-expansin in root hair growth

Abstract:
'Acid growth' is a fundamental theory of modern plant biology, where expansin acts as the executor by loosening the cell wall in a pH-dependent manner. But does this concept apply to all of the many proteins in the expansin superfamily, which is divided into EXPA, EXPB, EXLA and EXLB families. Are the proteins functionally diverse or redundant? In this study, we employed Arabidopsis root hairs, which undergo a specialized cell wall extension process and which express two dominant expansins, EXPA7 and EXPA18. Knocking out EXPA7 and EXPA18 blocked root hair elongation, suggesting root hair elongation requires a typical α-expansin-driven acid growth process. By assessing root hair growth complementation with reintroduced expansin superfamily members from the EXPA, EXPB, EXLA, and EXLB families, we identified functional diversities among different families and also among different members of the EXPA family. The most notable are EXPA13 and EXPA20, which lost a critical Asp residue that is essential for wall loosening activity.

In this study, we also identified the polar accumulation of canonical α-expansins in the cell wall at the root hair initiation domain, which occurs simultaneously the root hair bulging. Using pharmacological and genetic tools, we identified that canonical α-expansin is recruited by RHID-focused Rop GTPase through YIP4-mediated vesicular transport. This recruitment allows canonical α-expansin to track the secretion of cell wall secretory polysaccharides, thereby reaching the Rop GTPase-established polar region to facilitate polar growth.

About the Speaker:
Ze has been a Postdoctoral Fellow in Daniel Cosgrove's lab since Oct, 2021. In this lab, he focuses on the working mechanisms of expansin and partially involve cell wall mechanics.

Contact

  Daniel Cosgrove
  dcosgrove@psu.edu