title: Abscisic Acid Participates in the Control of Cell Cycle Initiation Through Heme Homeostasis in the Unicellular Red Alga Cyanidioschyzon merolae.
abstract: ABA is a phytohormone that is synthesized in response to abiotic stresses and other environmental changes, inducing various physiological responses. While ABA has been found in unicellular photosynthetic organisms, such as cyanobacteria and eukaryotic algae, its function in these organisms is poorly understood. Here, we found that ABA accumulated in the unicellular red alga Cyanidioschyzon merolae under conditions of salt stress and that the cell cycle G1/S transition was inhibited when ABA was added to the culture medium. A gene encoding heme-scavenging tryptophan-rich sensory protein-related protein (CmTSPO; CMS231C) was positively regulated by ABA, as in Arabidopsis, and CmTSPO bound heme in vitro. The intracellular content of total heme was increased by addition of ABA, but unfettered heme decreased, presumably due to scavenging by CmTSPO. The inhibition of DNA replication by ABA was negated by addition of heme to the culture medium. Thus, we propose a regulatory role for ABA and heme in algal cell cycle initiation. Finally, we found that a C. merolae mutant that is defective in ABA production was more susceptible to salt stress, indicating the importance of ABA to stress resistance in red algae.
authors.affiliation: Chemical Resources Laboratory, Tokyo Institute of Technology, 4259-R1-29 Nagatsuta, Midori-ku, Yokohama, 226-8503 Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Kobayashi
authors.affiliation: Graduate School of Horticulture, Chiba University, 648 Matsudo, Matsudo, Chiba, 271-8510 Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Ando
authors.affiliation: Graduate School of Horticulture, Chiba University, 648 Matsudo, Matsudo, Chiba, 271-8510 Japan.
authors.forename: Mitsumasa
authors.initials: M
authors.lastname: Hanaoka
authors.affiliation: Chemical Resources Laboratory, Tokyo Institute of Technology, 4259-R1-29 Nagatsuta, Midori-ku, Yokohama, 226-8503 Japan Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), Saitama, 332-0012 Japan kntanaka@res.titech.ac.jp.
authors.forename: Kan
authors.initials: K
authors.lastname: Tanaka
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism*; D002453:Cell Cycle; D004261:DNA Replication; D006418:Heme / Q000378:metabolism; D006706:Homeostasis; D010788:Photosynthesis; D010937:Plant Growth Regulators / Q000378:metabolism*; D000461:Rhodophyta / Q000235:genetics / Q000502:physiology*
chemical_list: D010937:Plant Growth Regulators; D006418:Heme; D000040:Abscisic Acid
keywords: ABA; Cell cycle; Cyanidioschyzon merolae; Heme; TSPO; Unfettered heme