title: Apical myosin XI anticipates F-actin during polarized growth of Physcomitrella patens cells.
abstract: Tip growth is essential for land colonization by bryophytes, plant sexual reproduction and water and nutrient uptake. Because this specialized form of polarized cell growth requires both a dynamic actin cytoskeleton and active secretion, it has been proposed that the F-actin-associated motor myosin XI is essential for this process. Nevertheless, a spatial and temporal relationship between myosin XI and F-actin during tip growth is not known in any plant cell. Here, we use the highly polarized cells of the moss Physcomitrella patens to show that myosin XI and F-actin localize, in vivo, at the same apical domain and that both signals fluctuate. Surprisingly, phase analysis shows that increase in myosin XI anticipates that of F-actin; in contrast, myosin XI levels at the tip fluctuate in identical phase with a vesicle marker. Pharmacological analysis using a low concentration of the actin polymerization inhibitor latrunculin B showed that the F-actin at the tip can be significantly diminished while myosin XI remains elevated in this region, suggesting that a mechanism exists to cluster myosin XI-associated structures at the cell's apex. In addition, this approach uncovered a mechanism for actin polymerization-dependent motility in the moss cytoplasm, where myosin XI-associated structures seem to anticipate and organize the actin polymerization machinery. From our results, we inferred a model where the interaction between myosin XI-associated vesicular structures and F-actin polymerization-driven motility function at the cell's apex to maintain polarized cell growth. We hypothesize this is a general mechanism for the participation of myosin XI and F-actin in tip growing cells.
authors.affiliation: Department of Biology and Biotechnology, Worcester Polytechnic Institute, Worcester, MA 01609, USA.
authors.forename: Fabienne
authors.initials: F
authors.lastname: Furt
authors.forename: Yen-Chun
authors.initials: YC
authors.lastname: Liu
authors.forename: Jeffrey P
authors.initials: JP
authors.lastname: Bibeau
authors.forename: Erkan
authors.initials: E
authors.lastname: Tüzel
authors.forename: Luis
authors.initials: L
authors.lastname: Vidali
mesh_terms: D000199:Actins / Q000378:metabolism*; D019068:Bryopsida / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism; D009218:Myosins / Q000378:metabolism*
chemical_list: D000199:Actins; D009218:Myosins