Short talk:
Tuning oxygenic photosynthesis to its energy limit: What the diversity of far-red light photoacclimation responses in cyanobacteria can teach us

Dennis Nürnberg

FU Berlin, Berlin, Germany

The discovery of cyanobacteria capable of harvesting far-red light has changed the paradigm that oxygenic photosynthesis is only driven by visible light and that the associated photochemistry is initiated exclusively by chlorophyll (chl) a. There are two known types of far- red photosynthesis. Firstly, a constitutive adaptation that uses chl d as the major photopigment, which is restricted to a single genus. More recently, an acclimation response known as Far-Red Light Photoacclimation (FaRLiP) was discovered, which uses chl f and is present in phylogenetically diverse cyanobacteria. FaRLiP involves the extensive remodelling of the photosynthetic machinery, via expression of a cluster of ~19 genes coding for paralogous subunits of PSI, PSII and phycobilisomes. Here, I will highlight the similarities and differences in FaRLiP at genome, protein, membrane and cellular levels by using bioinformatics, biochemical and biophysical methods. Using stringent far-red cultivation methods, numerous cyanobacteria were isolated, including a strain that only contains a partial FaRLiP cluster. This strain displays normal growth behaviour under far-red light despite lacking genes for far-red PSI, indicating that the minimal requirements for FaRLiP are less than the ~19 generally conserved clustered genes. Based on structural comparisons, first attempts were made to tune the absorption properties of a non-FaRLiP cyanobacterium towards far-red. We targeted PSII and introduced several far-red variants. All mutants showed the assembly of a functional PSII complex with chl a only, suggesting the involvement of specific assembly factors for the introduction of long- wavelength chlorophylls at specific positions in far-red PSII.


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