The cyanobacterium Synechococcus resists UV-B by exchanging photosystem II reaction-center D1 proteins

• Published in: Proceedings of the National Academy of Sciences - PNAS 1998-01, Vol.95 (1), p.364-369
• Main Authors: Campbell, D, Eriksson, M.J, Oquist, G, Gustafsson, P, Clarke, A.K
• Format: Article
• Language: English
• Subjects: Acclimatization; ARN MENSAJERO; ARN MESSAGER; Bacterial Proteins - metabolism; Bacterial Proteins - radiation effects; Biological Sciences; Botany; CONTENIDO PROTEICO; Cyanobacteria - genetics; Cyanobacteria - radiation effects; CYANOPHYTA; ELECTRON TRANSFER; Electrons; EXPRESION GENICA; EXPRESSION DES GENES; FOTOSINTESIS; FOTOSISTEMAS; Freshwater; GENE; GENE EXPRESSION; Gene Expression - radiation effects; Gene expression regulation; GENES; Lead; Light-Harvesting Protein Complexes; MESSENGER RNA; MUTANT; MUTANTES; MUTANTS; OXIDOREDUCTIONS; OXIRREDUCION; OXYDOREDUCTION; Oxygen; Photoinhibition; Photons; PHOTOSYNTHESE; PHOTOSYNTHESIS; Photosynthesis - radiation effects; Photosynthetic Reaction Center Complex Proteins - genetics; Photosynthetic Reaction Center Complex Proteins - metabolism; Photosynthetic Reaction Center Complex Proteins - radiation effects; Photosystem II; Photosystem II Protein Complex; PHOTOSYSTEME; PHOTOSYSTEMS; phycobiliprotein; Phycobilisome; PHYCOBILISOMES; PIGMENT; PIGMENTOS; PIGMENTS; Plant Proteins - metabolism; Plant Proteins - radiation effects; Plants; PROTEIN CONTENT; PROTEINAS; PROTEINE; PROTEINS; psbA; PSBAI GENE; PSBAII GENE; PSBAIII GENE; RADIACION ULTRAVIOLETA; RAYONNEMENT ULTRAVIOLET; RESISTANCE; STRUCTURAL GENES; Synechococcus; TENEUR EN PROTEINES; ULTRAVIOLET RADIATION; Ultraviolet Rays
• ISSN: 0027-8424; 1091-6490; 1091-6490
• DOI: 10.1073/pnas.95.1.364

Current ambient UV-B levels can significantly depress productivity in aquatic habitats, largely because UV-B inhibits several steps of photosynthesis, including the photooxidation of water catalyzed by photosystem II. We show that upon UV-B exposure the cyanobacterium Synechococcus sp. PCC 7942 rapidly changes the expression of a family of three psbA genes encoding photosystem II D1 proteins. In wild-type cells the psbAI gene is expressed constitutively, but strong accumulations of psbAII and psbAIII transcripts are induced within 15 min of moderate UV-B exposure (0.4 W/m2). This transcriptional response causes an exchange of two distinct photosystem II D1 proteins. D1:1 is encoded by psbAI, but on UV-B exposure, it is largely replaced by the alternate D1:2 form, encoded by both psbAII and psbAIII. The total content of D1 and other photosystem II reaction center protein, D2, remained unchanged throughout the UV exposure, as did the content and composition of the phycobilisome. Wild-type cells suffered only slight transient inhibition of photosystem II function under UV-B exposure. In marked contrast, under the same UV-B treatment, a mutant strain expressing only psbAI suffered severe (40%) and sustained inhibition of photosystem II function. Another mutant strain with constitutive expression of psbAII and psbAIII was almost completely resistant to the UV-B treatment, showing no inhibition of photosystem II function and only a slight drop in electron transport. In Synechococcus the rapid exchange of alternate D1 forms, therefore, accounts for much of the cellular resistance to UV-B inhibition of photosystem II activity and photosynthetic electron transport. This molecular plasticity may be an important element in community-level responses to UV-B, where susceptibility to UV-B inhibition of photosynthesis changes diurnally