title: Regulation of levels of actin threonine phosphorylation during life cycle of Physarum polycephalum.
abstract: Under various environmental stresses, the true slime mold Physarum polycephalum converts into dormant forms, such as microcysts, sclerotia, and spores, which can survive in adverse environments for a considerable period of time. In drought-induced sclerotia, actin is threonine phosphorylated, which blocks its ability to polymerize into filaments. It is known that fragmin and actin-fragmin kinase (AFK) mediate this phosphorylation event. In this work, we demonstrate that high levels of actin threonine phosphorylation are also found in other dormant cells, including microcysts and spores. As the threonine phosphorylation of actin in microcysts and sclerotia were induced by drought stress but not by other stresses, we suggest that drought stress is essential for actin phosphorylation in both cell types. Although characteristic filamentous actin structures (dot- or rod-like structures) were observed in microcysts, sclerotia, and spores, actin phosphorylation was not required for the formation of these structures. Prior to the formation of both microcysts and sclerotia, AFK mRNA expression was activated transiently, whereas fragmin mRNA levels decreased. Our results suggest that drought stress and AFK might be involved in the threonine phosphorylation of actin.
authors.affiliation: Department of Biology, Ochanomizu University, Bunkyo-ku, Tokyo 112-8610, Japan. yukih@cc.ocha.ac.jp
authors.forename: Yuki
authors.initials: Y
authors.lastname: Shirai
authors.forename: Narie
authors.initials: N
authors.lastname: Sasaki
authors.forename: Yoshiro
authors.initials: Y
authors.lastname: Kishi
authors.forename: Akiko
authors.initials: A
authors.lastname: Izumi
authors.forename: Kie
authors.initials: K
authors.lastname: Itoh
authors.forename: Masazumi
authors.initials: M
authors.lastname: Sameshima
authors.forename: Tetsuyuki
authors.initials: T
authors.lastname: Kobayashi
authors.forename: Kimiko
authors.initials: K
authors.lastname: Murakami-Murofushi
mesh_terms: D000199:Actins / Q000737:chemistry* / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D003681:Dehydration; D004190:Disasters; D015180:Electrophoresis, Gel, Two-Dimensional; D004591:Electrophoresis, Polyacrylamide Gel; D008018:Life Cycle Stages; D010766:Phosphorylation; D016839:Physarum polycephalum / Q000254:growth & development* / Q000502:physiology; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D015800:Protozoan Proteins / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013912:Threonine / Q000378:metabolism*
chemical_list: D000199:Actins; D015800:Protozoan Proteins; D012333:RNA, Messenger; D013912:Threonine; C074377:actin kinase; D017346:Protein Serine-Threonine Kinases