title: Plasma membrane protein OsMCA1 is involved in regulation of hypo-osmotic shock-induced Ca2+ influx and modulates generation of reactive oxygen species in cultured rice cells.
abstract: BACKGROUND
  Mechanosensing and its downstream responses are speculated to involve sensory complexes containing Ca2+-permeable mechanosensitive channels. On recognizing osmotic signals, plant cells initiate activation of a widespread signal transduction network that induces second messengers and triggers inducible defense responses. Characteristic early signaling events include Ca2+ influx, protein phosphorylation and generation of reactive oxygen species (ROS). Pharmacological analyses show Ca2+ influx mediated by mechanosensitive Ca2+ channels to influence induction of osmotic signals, including ROS generation. However, molecular bases and regulatory mechanisms for early osmotic signaling events remain poorly elucidated.
  
  
  RESULTS
  We here identified and investigated OsMCA1, the sole rice homolog of putative Ca2+-permeable mechanosensitive channels in Arabidopsis (MCAs). OsMCA1 was specifically localized at the plasma membrane. A promoter-reporter assay suggested that OsMCA1 mRNA is widely expressed in seed embryos, proximal and apical regions of shoots, and mesophyll cells of leaves and roots in rice. Ca2+ uptake was enhanced in OsMCA1-overexpressing suspension-cultured cells, suggesting that OsMCA1 is involved in Ca2+ influx across the plasma membrane. Hypo-osmotic shock-induced ROS generation mediated by NADPH oxidases was also enhanced in OsMCA1-overexpressing cells. We also generated and characterized OsMCA1-RNAi transgenic plants and cultured cells; OsMCA1-suppressed plants showed retarded growth and shortened rachises, while OsMCA1-suppressed cells carrying Ca2+-sensitive photoprotein aequorin showed partially impaired changes in cytosolic free Ca2+ concentration ([Ca2+]cyt) induced by hypo-osmotic shock and trinitrophenol, an activator of mechanosensitive channels.
  
  
  CONCLUSIONS
  We have identified a sole MCA ortholog in the rice genome and developed both overexpression and suppression lines. Analyses of cultured cells with altered levels of this putative Ca2+-permeable mechanosensitive channel indicate that OsMCA1 is involved in regulation of plasma membrane Ca2+ influx and ROS generation induced by hypo-osmotic stress in cultured rice cells. These findings shed light on our understanding of mechanical sensing pathways.
authors.affiliation: Department of Applied Biological Science, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba, Japan.
authors.forename: Takamitsu
authors.initials: T
authors.lastname: Kurusu
authors.forename: Daisuke
authors.initials: D
authors.lastname: Nishikawa
authors.forename: Yukari
authors.initials: Y
authors.lastname: Yamazaki
authors.forename: Mariko
authors.initials: M
authors.lastname: Gotoh
authors.forename: Masataka
authors.initials: M
authors.lastname: Nakano
authors.forename: Haruyasu
authors.initials: H
authors.lastname: Hamada
authors.forename: Takuya
authors.initials: T
authors.lastname: Yamanaka
authors.forename: Kazuko
authors.initials: K
authors.lastname: Iida
authors.forename: Yuko
authors.initials: Y
authors.lastname: Nakagawa
authors.forename: Hikaru
authors.initials: H
authors.lastname: Saji
authors.forename: Kazuo
authors.initials: K
authors.lastname: Shinozaki
authors.forename: Hidetoshi
authors.initials: H
authors.lastname: Iida
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Kuchitsu
mesh_terms: D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D012275:Oryza / Q000235:genetics / Q000378:metabolism*; D009997:Osmotic Pressure / Q000502:physiology*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism*
chemical_list: D010940:Plant Proteins; D017382:Reactive Oxygen Species; D002118:Calcium