title: A Processive Arabidopsis Formin Modulates Actin Filament Dynamics in Association with Profilin.
abstract: Formins are conserved regulators of actin cytoskeletal organization and dynamics that have been implicated to be important for cell division and cell polarity. The mechanism by which diverse formins regulate actin dynamics in plants is still not well understood. Using in vitro single-molecule imaging technology, we directly observed that the FH1-FH2 domain of an Arabidopsis thaliana formin, AtFH14, processively attaches to the barbed end of actin filaments as a dimer and slows their elongation rate by 90%. The attachment persistence of FH1-FH2 is concentration dependent. Furthermore, by use of the triple-color total internal reflection fluorescence microscopy, we found that ABP29, a barbed-end capping protein, competes with FH1-FH2 at the filament barbed end, where its binding is mutually exclusive with AtFH14. In the presence of different plant profilin isoforms, FH1-FH2 enhances filament elongation rates from about 10 to 42 times. Filaments buckle when FH1-FH2 is anchored specifically to cover slides, further indicating that AtFH14 moves processively on the elongating barbed end. At high concentration, AtFH14 bundles actin filaments randomly into antiparallel or parallel spindle-like structures; however, the FH1-FH2-mediated bundles become thinner and longer in the presence of plant profilins. This is the direct demonstration of a processive formin from plants. Our results also illuminate the molecular mechanism of AtFH14 in regulating actin dynamics via association with profilin.
authors.affiliation: Key Laboratory of Cell Proliferation and Regulation Biology of Ministry of Education, College of Life Science, Beijing Normal University, Beijing 100875, People's Republic of China.
authors.forename: Sha
authors.initials: S
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Cell Proliferation and Regulation Biology of Ministry of Education, College of Life Science, Beijing Normal University, Beijing 100875, People's Republic of China.
authors.forename: Chang
authors.initials: C
authors.lastname: Liu
authors.affiliation: Key Laboratory of Cell Proliferation and Regulation Biology of Ministry of Education, College of Life Science, Beijing Normal University, Beijing 100875, People's Republic of China.
authors.forename: Jiaojiao
authors.initials: J
authors.lastname: Wang
authors.affiliation: Key Laboratory of Cell Proliferation and Regulation Biology of Ministry of Education, College of Life Science, Beijing Normal University, Beijing 100875, People's Republic of China.
authors.forename: Zhanhong
authors.initials: Z
authors.lastname: Ren
authors.affiliation: Department of Biological Sciences, Purdue University, Hansen Life Sciences Research Building, West Lafayette, IN 47907-2064, USA.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Staiger
authors.affiliation: Key Laboratory of Cell Proliferation and Regulation Biology of Ministry of Education, College of Life Science, Beijing Normal University, Beijing 100875, People's Republic of China. Electronic address: hren@bnu.edu.cn.
authors.forename: Haiyun
authors.initials: H
authors.lastname: Ren
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism*; D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D051304:Profilins / Q000378:metabolism*; D020033:Protein Isoforms / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D051304:Profilins; D020033:Protein Isoforms
keywords: TIRF microscopy; actin bundle; capping protein; processive formin; profilin; single molecule