title: A plastidic ABC protein involved in intercompartmental communication of light signaling.
abstract: Plants perceive light via specialized photoreceptors of which the phytochromes (phyA-E), absorbing far-red (FR) and red light (R) are best understood. Several nuclear and cytoplasmic proteins have been characterized whose deficiencies lead to changes in light-dependent morphological responses and gene expression. However, no plastid protein has yet been identified to play a role in phytochrome signal transduction. We have isolated a new Arabidopsis mutant, laf (long after FR) 6, with reduced responsiveness preferentially toward continuous FR light. The disrupted gene in laf6 encodes a novel plant ATP-binding-cassette (atABC1) protein of 557 amino acids with high homology to ABC-like proteins from lower eukaryotes. In contrast to lower eukaryotic ABCs, however, atABC1 contains an N-terminal transit peptide, which targets it to chloroplasts. atABC1 deficiency in laf6 results in an accumulation of the chlorophyll precursor protoporphyrin IX and in attenuation of FR-regulated gene expression. The long hypocotyl phenotype of laf6 and the accumulation of protoporphyrin IX in the mutant can be recapitulated by treating wild-type (WT) seedlings with flumioxazin, a protoporphyrinogen IX oxidase (PPO) inhibitor. Moreover, protoporphyrin IX accumulation in flumioxazin-treated WT seedlings can be reduced by overexpression of atABC1. Consistent with the notion that ABC proteins are involved in transport, these observations suggest that functional atABC1 is required for the transport and correct distribution of protoporphyrin IX, which may act as a light-specific signaling factor involved in coordinating intercompartmental communication between plastids and the nucleus.
authors.affiliation: Laboratory of Plant Molecular Biology, Rockefeller University, 1230 York Avenue, New York, New York 10021-6399, USA.
authors.forename: S G
authors.initials: SG
authors.lastname: Møller
authors.forename: T
authors.initials: T
authors.lastname: Kunkel
authors.forename: N H
authors.initials: NH
authors.lastname: Chua
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000502:physiology*; D029681:Arabidopsis Proteins; D048588:Benzoxazines; D003624:Darkness; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018506:Gene Expression Regulation, Plant; D008027:Light; D008969:Molecular Sequence Data; D010078:Oxazines / Q000494:pharmacology; D010088:Oxidoreductases / Q000037:antagonists & inhibitors / Q000378:metabolism; D044925:Oxidoreductases Acting on CH-CH Group Donors; D010797:Phthalimides / Q000494:pharmacology; D010834:Phytochrome / Q000378:metabolism; D051942:Phytochrome A; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D018087:Plastids / Q000502:physiology*; D050768:Protoporphyrinogen Oxidase; D011524:Protoporphyrins / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction / Q000502:physiology* / Q000528:radiation effects
chemical_list: D018528:ATP-Binding Cassette Transporters; D029681:Arabidopsis Proteins; D048588:Benzoxazines; D004791:Enzyme Inhibitors; D010078:Oxazines; C497973:PHYA protein, Arabidopsis; D010797:Phthalimides; D051942:Phytochrome A; D010940:Plant Proteins; D011524:Protoporphyrins; D010834:Phytochrome; C028025:protoporphyrin IX; D010088:Oxidoreductases; D044925:Oxidoreductases Acting on CH-CH Group Donors; D050768:Protoporphyrinogen Oxidase; C106487:flumioxazin