title: Plasma membrane-associated SCAR complex subunits promote cortical F-actin accumulation and normal growth characteristics in Arabidopsis roots.
abstract: The ARP2/3 complex, a highly conserved nucleator of F-actin polymerization, and its activator, the SCAR complex, have been shown to play important roles in leaf epidermal cell morphogenesis in Arabidopsis. However, the intracellular site(s) and function(s) of SCAR and ARP2/3 complex-dependent actin polymerization in plant cells remain unclear. We demonstrate that putative SCAR complex subunits BRK1 and SCAR1 are localized to the plasma membrane at sites of cell growth and wall deposition in expanding cells of leaves and roots. BRK1 localization is SCAR-dependent, providing further evidence of an association between these proteins in vivo. Consistent with plasma membrane localization of SCAR complex subunits, cortical F-actin accumulation in root tip cells is reduced in brk1 mutants. Moreover, mutations disrupting the SCAR or ARP2/3 complex reduce the growth rate of roots and their ability to penetrate semi-solid medium, suggesting reduced rigidity. Cell walls of mutant roots exhibit abnormal structure and composition at intercellular junctions where BRK1 and SCAR1 are enriched in the adjacent plasma membrane. Taken together, our results suggest that SCAR and ARP2/3 complex-dependent actin polymerization promotes processes at the plasma membrane that are important for normal growth and wall assembly.
authors.affiliation: University of California San Diego, La Jolla, CA 92093-0116, USA.
authors.forename: Julia
authors.initials: J
authors.lastname: Dyachok
authors.forename: Mon-Ray
authors.initials: MR
authors.lastname: Shao
authors.forename: Kevin
authors.initials: K
authors.lastname: Vaughn
authors.forename: Andrew
authors.initials: A
authors.lastname: Bowling
authors.forename: Michelle
authors.initials: M
authors.lastname: Facette
authors.forename: Stevan
authors.initials: S
authors.lastname: Djakovic
authors.forename: Lauren
authors.initials: L
authors.lastname: Clark
authors.forename: Laurie
authors.initials: L
authors.lastname: Smith
mesh_terms: D051376:Actin-Related Protein 2-3 Complex / Q000378:metabolism; D000199:Actins / Q000378:metabolism*; D017360:Arabidopsis / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism / Q000648:ultrastructure; D029681:Arabidopsis Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism* / Q000648:ultrastructure; D002473:Cell Wall / Q000378:metabolism / Q000648:ultrastructure; D008565:Membrane Proteins / Q000378:metabolism; D008861:Microsomes / Q000378:metabolism / Q000648:ultrastructure; D046912:Multiprotein Complexes / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D010936:Plant Extracts / Q000378:metabolism; D018517:Plant Roots / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism / Q000648:ultrastructure; D011485:Protein Binding; D021122:Protein Subunits / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism
chemical_list: D051376:Actin-Related Protein 2-3 Complex; D000199:Actins; D029681:Arabidopsis Proteins; D008565:Membrane Proteins; D046912:Multiprotein Complexes; D010936:Plant Extracts; D021122:Protein Subunits; D011993:Recombinant Fusion Proteins