title: Activation of Arp2/3 complex-dependent actin polymerization by plant proteins distantly related to Scar/WAVE.
abstract: The Arp2/3 complex, a highly conserved nucleator of F-actin polymerization, plays a key role in the regulation of actin dynamics eukaryotic cells. In animal cells and yeasts, Wiskott-Aldrich Syndrome protein (WASP)/suppressor of cAMP receptor (Scar)/WASP family verprolin homologous (WAVE) family proteins activate the Arp2/3 complex in response to localized cues. Like other eukaryotes, plants have an Arp2/3 complex, which has recently been shown to play an important role in F-actin organization and cell morphogenesis. However, no activators of the Arp2/3 complex have been identified in plants, which lack obvious homologs of WASP/Scar/WAVE family proteins. Here, we identify a family of Scar/WAVE-related plant Arp2/3 activators. Like Scar/WAVE proteins, four proteins identified in Arabidopsis thaliana (AtSCAR1 to AtSCAR4) and one in maize (ZmSCAR1) have a C-terminal WASP homology 2 (WH2)/acidic (WA)-verprolin homology/cofilin homology/acidic (VCA)-like domain, which we show can activate the bovine Arp2/3 complex. At their N termini, AtSCAR1 to ATSCAR4, along with a fifth protein lacking a VCA/WA-like domain at its C terminus (At4g18600), are related to the N-terminal Scar homology domains of Scar/WAVE family proteins. Analysis of gene expression patterns suggests functional redundancy among members of the AtSCAR family. Full-length AtSCAR1 and ATSCAR3 proteins and their Scar homology domains bind in vitro to AtBRICK 1 (AtBRK1), the Arabidopsis homolog of HSPC300, a WAVE-binding protein recently identified as a component of a complex implicated in the regulation of Scar/WAVE activity. Thus, AtSCAR proteins are likely to function in association with AtBRK1, and perhaps other Arabidopsis homologs of WAVE complex components, to regulate activation of the Arp2,3 complex in vivo.
authors.affiliation: Section of Cell and Developmental Biology, University of California at San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0116, USA.
authors.forename: Mary
authors.initials: M
authors.lastname: Frank
authors.forename: Coumaran
authors.initials: C
authors.lastname: Egile
authors.forename: Julia
authors.initials: J
authors.lastname: Dyachok
authors.forename: Stevan
authors.initials: S
authors.lastname: Djakovic
authors.forename: Michelle
authors.initials: M
authors.lastname: Nolasco
authors.forename: Rong
authors.initials: R
authors.lastname: Li
authors.forename: Laurie G
authors.initials: LG
authors.lastname: Smith
mesh_terms: D051377:Actin-Related Protein 2; D051376:Actin-Related Protein 2-3 Complex; D051378:Actin-Related Protein 3; D000199:Actins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D018744:DNA, Plant / Q000235:genetics; D017343:Genes, Plant; D008840:Microfilament Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D051300:Wiskott-Aldrich Syndrome Protein Family; D003313:Zea mays / Q000235:genetics / Q000378:metabolism
chemical_list: C512742:ARP2 protein, Arabidopsis; D051377:Actin-Related Protein 2; D051376:Actin-Related Protein 2-3 Complex; D051378:Actin-Related Protein 3; D000199:Actins; D029681:Arabidopsis Proteins; C493650:BRK1 protein, Arabidopsis; C478027:DIS1 protein, Arabidopsis; D018744:DNA, Plant; D008840:Microfilament Proteins; D046912:Multiprotein Complexes; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; D051300:Wiskott-Aldrich Syndrome Protein Family