title: Arabidopsis FIMBRIN5, an actin bundling factor, is required for pollen germination and pollen tube growth.
abstract: Actin cables in pollen tubes serve as molecular tracks for cytoplasmic streaming and organelle movement and are formed by actin bundling factors like villins and fimbrins. However, the precise mechanisms by which actin cables are generated and maintained remain largely unknown. Fimbrins comprise a family of five members in Arabidopsis thaliana. Here, we characterized a fimbrin isoform, Arabidopsis FIMBRIN5 (FIM5). Our results show that FIM5 is required for the organization of actin cytoskeleton in pollen grains and pollen tubes, and FIM5 loss-of-function associates with a delay of pollen germination and inhibition of pollen tube growth. FIM5 decorates actin filaments throughout pollen grains and tubes. Actin filaments become redistributed in fim5 pollen grains and disorganized in fim5 pollen tubes. Specifically, actin cables protrude into the extreme tips, and their longitudinal arrangement is disrupted in the shank of fim5 pollen tubes. Consequently, the pattern and velocity of cytoplasmic streaming were altered in fim5 pollen tubes. Additionally, loss of FIM5 function rendered pollen germination and tube growth hypersensitive to the actin-depolymerizing drug latrunculin B. In vitro biochemical analyses indicated that FIM5 exhibits actin bundling activity and stabilizes actin filaments. Thus, we propose that FIM5 regulates actin dynamics and organization during pollen germination and tube growth via stabilizing actin filaments and organizing them into higher-order structures.
authors.affiliation: Center for Signal Transduction and Metabolomics, Key Laboratory of Photosynthesis and Environmental Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.
authors.forename: Youjun
authors.initials: Y
authors.lastname: Wu
authors.forename: Jin
authors.initials: J
authors.lastname: Yan
authors.forename: Ruihui
authors.initials: R
authors.lastname: Zhang
authors.forename: Xiaolu
authors.initials: X
authors.lastname: Qu
authors.forename: Sulin
authors.initials: S
authors.lastname: Ren
authors.forename: Naizhi
authors.initials: N
authors.lastname: Chen
authors.forename: Shanjin
authors.initials: S
authors.lastname: Huang
mesh_terms: D000199:Actins / Q000378:metabolism* / Q000648:ultrastructure; D017360:Arabidopsis / Q000033:anatomy & histology / Q000502:physiology; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D003433:Crosses, Genetic; D003595:Cytoplasmic Streaming; D005816:Genetic Complementation Test; D055993:Germ Cells, Plant / Q000166:cytology / Q000378:metabolism; D018525:Germination / Q000502:physiology*; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D008840:Microfilament Proteins / Q000235:genetics / Q000378:metabolism*; D011058:Pollen / Q000378:metabolism* / Q000648:ultrastructure; D053205:Pollen Tube / Q000254:growth & development* / Q000648:ultrastructure; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D000199:Actins; D029681:Arabidopsis Proteins; D008562:Membrane Glycoproteins; D008840:Microfilament Proteins; D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; C026742:plastin