Functional flexibility of cyanobacterial light harvesting phycobilisomes enable acclimation to the complex light regime of mixing marine water columns. (29th August 2022)

• Record Type: Journal Article
• Authors: Bezalel‐Hazony, Noa; Zer, Hagit; Nathanson, Shiri; Shevtsov‐Tal, Sofia; Ostersetzer‐Biran, Oren; Keren, Nir
• Is Part Of: FEBS journal. Volume 290:Number 2(2023)
• Page Start: 400
• Page End: 411
• Publication Date: 2022-08-29
• Subjects: energy transfer -- light acclimation -- light harvesting -- phycobilisome; Biochemistry -- Periodicals; Molecular biology -- Periodicals; Pathology, Molecular -- Periodicals; 572
• DOI: 10.1111/febs.16597
• Languages: English
• ISSNs: 1742-464X

Abstract

Abstract : The light environment in a mixing water column is arguably the most erratic condition under which photosynthesis functions. Shifts in light intensity, by an order of magnitude, can occur over the time scale of hours. In marine Synechococcus, light is harvested by massive, membrane attached, phycobilisome chromophore‐protein complexes (PBS). We examined the ability of a phycobilisome‐containing marine Synechococcus strain (WH8102) to acclimate to illumination perturbations on this scale. Although changes in pigment composition occurred gradually over the course of days, we did observe significant and reversible changes in the pigment's fluorescence emission spectra on a time scale of hours. Upon transition to ten‐fold higher intensities, we observed a decrease in the energy transferred to Photosystem II. At the same time, the spectral composition of PBS fluorescence emission shifted. Unlike fluorescence quenching mechanisms, this phenomenon resulted in increased fluorescence intensities. These data suggest a mechanism by which marine Synechococcus WH8102 detaches hexamers from the phycobilisome structure. The fluorescence yield of these uncoupled hexamers is high. The detachment process does not require protein synthesis as opposed to reattachment. Hence, the most likely process would be the degradation and resynthesis of labile PBS linker proteins. Experiments with additional species yielded similar results, suggesting that this novel mechanism might be broadly used among PBS‐containing organisms. Abstract : We show that Synechococcus cyanobacteria can reversibly tune their phycobilisome (PBS) structure and energy transfer properties, to fit the erratic light intensity regime of a mixing water column. This can be achieved within a time scale of hours. We propose a new mechanism in which these organisms can temporarily detach protein–chromophore complexes of their PBS rods, giving them an ability to fine‐tune the absorbed energy.