title: Cyanobacterial psbA families in Anabaena and Synechocystis encode trace, constitutive and UVB-induced D1 isoforms.
abstract: Cyanobacteria cope with UVB induced photoinhibition of Photosystem II by regulating multiple psbA genes to boost the expression of D1 protein (in Synechocystis sp. PCC6803), or to exchange the constitutive D1:1 protein to an alternate D1:2 isoform (in Synechococcus sp. PCC7942). To define more general patterns of cyanobacterial psbA expression, we applied moderately photoinhibitory UVB to Anabaena sp. PCC7120 and tracked the expression of its five psbA genes. psbAI, encoding a D1:1 protein isoform characterized by a Gln130, represented the majority of the psbA transcript pool under control conditions. psbAI transcripts decreased upon UVB treatment but the total psbA transcript pool increased 3.5 fold within 90 min as a result of sharply increased psbAII, psbAIV and psbAIII transcripts encoding an alternate D1:2 protein isoform characterized by Glu130, similar to that of Synechococcus. Upon UVB treatment the relaxation of flash induced chlorophyll fluorescence showed a characteristic acceleration of a decay phase likely associated with the exchange from the D1:1 protein isoform encoded by psbAI to the alternate D1:2 isoform encoded by psbAIV, psbAII and psbAIII. Throughout the UVB treatment the divergent psbA0 made only a trace contribution to the total psbA transcript pool. This suggests a similarity to the divergent psbAI gene from Synechocystis, whose natural expression we demonstrate for the first time at a trace level similar to psbA0 in Anabaena. These trace-expressed psbA genes in two different cyanobacteria raise questions concerning the functions of these divergent genes.
authors.affiliation: Department of Biology, Mount Allison University, Sackville, NB, Canada E4L1G7.
authors.forename: Cosmin I
authors.initials: CI
authors.lastname: Sicora
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Appleton
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Brown
authors.forename: Jonathon
authors.initials: J
authors.lastname: Chung
authors.forename: Jillian
authors.initials: J
authors.lastname: Chandler
authors.forename: Amanda M
authors.initials: AM
authors.lastname: Cockshutt
authors.forename: Imre
authors.initials: I
authors.lastname: Vass
authors.forename: Douglas A
authors.initials: DA
authors.lastname: Campbell
mesh_terms: D000595:Amino Acid Sequence; D017033:Anabaena / Q000201:enzymology* / Q000235:genetics / Q000528:radiation effects*; D015870:Gene Expression / Q000187:drug effects; D014644:Genetic Variation; D008969:Molecular Sequence Data; D045332:Photosystem II Protein Complex / Q000235:genetics* / Q000528:radiation effects; D020033:Protein Isoforms / Q000235:genetics / Q000528:radiation effects; D046939:Synechocystis / Q000201:enzymology* / Q000235:genetics / Q000528:radiation effects*; D014466:Ultraviolet Rays
chemical_list: D045332:Photosystem II Protein Complex; D020033:Protein Isoforms; C422369:photosystem II, psbA subunit