Far-red absorption and light-use efficiency trade-offs in chlorophyll f photosynthesis

Abstract

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The natural design for harvesting far-red light: the antenna increases both absorption and quantum efficiency of Photosystem II

“…Cells were excited both at low power, when most PSII RCs are in the open state, and at high power in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), when PSII RCs are in the closed state, to separate the spectroscopic contribution of PSII from that of PSI and estimate the photochemical yield of PSII. Experiments were performed at two different excitation wavelengths, 400 nm (more selective for the photosystems and yielding results similar to our previous work 18 ) and 577 nm (more selective for the phycobiliproteins). Due to the heterogeneity of the photosynthetic apparatus of FRL-cells, both WL-PBSs and FRL-BCs are excited at 577 nm.…”

“…The one at shorter wavelengths is due to WL-PSII and the WL-PBSs that are maintained in FRL, in line with previous findings on another FaRLiP strain 17 . The band above 700 nm is due to FRL-PSII and the FRL-BCs 18 , while the shoulder extending up to 800 nm stems from the extremely red-shifted Chls f typical for FRL-PSI 16,18,25 . Upon 580-nm excitation, which is more selective for the bilins, the far-red band is more blue-shifted than upon 400-nm excitation due to a larger contribution from FRL-BCs.…”

“…FRL-induced photoacclimation (FaRLiP) involves replacing the photosystems expressed in WL (WL-photosystems) with new photosystems containing FRL-specific paralog protein subunits. FRL-photosystems incorporate a small number of chlorophylls f and d allowing them to absorb up to 750 nm (FRL-PSII) [16][17][18] , or even 800 nm (FRL-PSI) 16,[18][19][20] . Under FRL, new APC paralog subunits are also produced, which assemble into bicylindrical cores (FRL-BCs) 21,22 .…”

“…Some strains possess only FRL-BCs in FRL 22 , while in others the peripheral rods of phycocyanin and phycoerythrin are associated with FRL-BCs 23 . Finally, besides producing FRL-photosystems and FRL-BCs, some strains were shown to maintain variable amounts of WL-photosystems and/or WL-PBSs after weeks of acclimation to FRL 17,18,21 .…”

“…In order to achieve high biomass yields, however, the newly engineered photosynthetic units need to preserve high photochemical yields. In this respect, we have recently shown that the insertion of Chl f slows down photochemistry in both photosystems and significantly decreases the efficiency of FRL-PSII in comparison to WL-PSII 18 . This effect is ascribed to (i) a slower charge separation by the RCs due to a red-shifted primary electron donor and (ii) a less effective connectivity between the few FRLabsorbing Chls surrounded by a majority of Chls a.…”