AME 65:1-14 (2011)  -  DOI: https://doi.org/10.3354/ame01528

ABSTRACT: Expression of 3 gene families involved with photoacclimation— psbA (encoding the photosystem II reaction center protein D1), hli (encoding the high-light inducible proteins), and ptox (encoding the plastid terminal oxidase)—was compared in the marine cyanobacteria Synechococcus WH8102 and Prochlorococcus MED4 acclimated to either low or high light. These 2 strains, adapted for growth in oligotrophic marine environments, have distinct light-harvesting systems and respond differently to changes in irradiance. In response to growth at higher irradiance, Synechococcus WH8102 increased expression of the psbA multigene family ( psbA1–4) 5-fold. Within this gene ­family, the expression of psbA2 increased 60-fold. Expression of 4 hli genes increased 2- to 5-fold, whereas expression of the ptox gene decreased 3-fold. In comparison, expression of the psbA gene increased 2-fold in Prochlorococcus MED4 cultures grown at higher irradiances. Expression of the Prochlorococcus MED4 hli6–9 and hli16–19 operons increased 11- to 14-fold, while ptox expression increased 3-fold. Using psbA induction as a standard for acclimation to changes in irradiance, we observed that the induction ratio of ptox: psbA1 and hli: psbA1 was 144 and 70 times greater, respectively, in Prochlorococcus MED4 compared with Synechococcus WH8102. These observations suggest that induction of ptox and hli may play a key role in the phototolerance of Prochlorococcus MED4. Conversely, the induction of psbA, and the synthesis of the PSII reaction center protein D1, may be critical for the acclimation of Synechococcus WH8102 to high irradiances.

KEY WORDS: Synechococcus WH8102 · Prochlorococcus MED4 · Photoacclimation · Photoinhibition · Gene expression · psbA · hli · ptox · Fluorescence characterization · Carbon fixation