title: A mutation in the Neurospora crassa actin gene results in multiple defects in tip growth and branching.
abstract: Actin has a pivotal function in hyphal morphogenesis in filamentous fungi, but it is not certain whether its function is equivalent to that of a morphogen, or if it is simply part of a mechanism that executes orders given by another regulatory entity. To address this question we selected for cytochalasin A resistance and isolated act1, the first actin mutant in Neurospora crassa. This mutant branches apically and shows an altered distribution of actin at the tip. Based on the properties of this mutant, we propose a model of tip growth and branching in which actin effects tip growth by regulating the rate of vesicle flow from proximal to distal regions of a hypha, thereby controlling the tip-high gradient of cytoplasmic calcium. The actin-controlled calcium gradient at the tip is necessary for maintenance of tip growth as well as the dominance of one polarized site at the hyphal tip. The phenotype of act1 indicates that actin controls the balance between lateral and apical branching.
authors.affiliation: Department of Botany, University of British Columbia, Vancouver, BC, Canada V6T 1Z4.
authors.forename: Aleksandra
authors.initials: A
authors.lastname: Virag
authors.forename: Anthony J F
authors.initials: AJ
authors.lastname: Griffiths
mesh_terms: D000199:Actins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D016764:Cell Polarity; D003001:Cloning, Molecular; D003572:Cytochalasins / Q000494:pharmacology; D003593:Cytoplasm / Q000737:chemistry; D022162:Cytoplasmic Vesicles / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000502:physiology; D025141:Drug Resistance, Fungal / Q000235:genetics; D005656:Fungal Proteins / Q000235:genetics / Q000502:physiology; D005800:Genes, Fungal; D025301:Hyphae / Q000166:cytology / Q000254:growth & development; D009024:Morphogenesis / Q000235:genetics; D009154:Mutation; D009492:Neurospora crassa / Q000166:cytology / Q000235:genetics* / Q000254:growth & development*; D012641:Selection, Genetic; D013696:Temperature
chemical_list: D000199:Actins; D003572:Cytochalasins; D003598:Cytoskeletal Proteins; D005656:Fungal Proteins; C031218:cytochalasin A; D002118:Calcium