title: Brefeldin a inhibits circadian remodeling of chloroplast structure in the dinoflagellate gonyaulax.
abstract: Circadian increases in the rate of carbon fixation in the dinoflagellate Gonyaulax are correlated with extensive plastid remodeling. One marker for this remodeling is mobilization of ribulose bisphosphate carboxylase/oxygenase (Rubisco) from the plastid periphery to plastid regions nearer the cell center called pyrenoids. Nuclear-encoded proteins such as Rubisco transit through the Golgi in dinoflagellates; hence, we blocked protein import into the plastids using Brefeldin A (BFA) to explore the mechanism for plastid remodeling. We find that pyrenoid formation normally occurs concurrently with increased Rubisco synthesis rates in vivo, and when BFA is given prior to the onset of Rubisco synthesis, pyrenoid formation is partially or completely inhibited by 0.1 or 0.3 microg/mL BFA, respectively. Rubisco synthesis itself is not affected, and BFA-treated cells accumulate Rubisco in novel structures we term BFA bodies. Interestingly, when given just after the onset of Rubisco synthesis, BFA delays but does not block Rubisco mobilization, suggesting that a timing signal for plastid remodeling is delivered to the organelles at the same time as newly synthesized Rubisco. BFA also inhibits the circadian increases in carbon fixation rates, supporting the hypothesis that the biochemical basis for this circadian rhythm may be Rubisco distribution within the plastid.
authors.affiliation: Institut de Recherche en Biologie Végétale, Département de Sciences Biologiques, Université de Montréal, 4101 Sherbrooke est, Montreal, Quebec, Canada H1X2B2.
authors.forename: Nasha
authors.initials: N
authors.lastname: Nassoury
authors.forename: Yunling
authors.initials: Y
authors.lastname: Wang
authors.forename: David
authors.initials: D
authors.lastname: Morse
mesh_terms: D000818:Animals; D020126:Brefeldin A / Q000494:pharmacology*; D002245:Carbon Dioxide / Q000378:metabolism; D002736:Chloroplasts / Q000648:ultrastructure*; D002940:Circadian Rhythm / Q000187:drug effects* / Q000502:physiology; D004141:Dinoflagellida / Q000187:drug effects* / Q000648:ultrastructure; D015180:Electrophoresis, Gel, Two-Dimensional; D016253:Microscopy, Immunoelectron; D018087:Plastids / Q000201:enzymology / Q000378:metabolism; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism
chemical_list: D002245:Carbon Dioxide; D020126:Brefeldin A; D012273:Ribulose-Bisphosphate Carboxylase