The cyanobacterium Synechococcus resists UV-B by exchanging photosystem II reaction-center D1 proteins
| Autor: | Adrian K. Clarke, Mats-Jerry Eriksson, Douglas A. Campbell, Gunnar Öquist, Petter Gustafsson |
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| Jazyk: | angličtina |
| Rok vydání: | 1998 |
| Předmět: |
Photosynthetic reaction centre
Multidisciplinary biology Photosystem II Ultraviolet Rays Phycobiliprotein Photosynthetic Reaction Center Complex Proteins Light-Harvesting Protein Complexes Gene Expression Photosystem II Protein Complex macromolecular substances Biological Sciences Photosynthesis Synechococcus biology.organism_classification Photosystem I Cyanobacteria Bacterial Proteins Botany Biophysics Phycobilisomes Phycobilisome Photosystem Plant Proteins |
| Popis: | 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/m 2 ). 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. |
| Databáze: | OpenAIRE |
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