Abstract
The cyclic electron transport (CET), after the linear electron transport (LET), is another important electron transport pathway during the light reactions of photosynthesis. The proton gradient regulation 5 (PGR5)/PRG5-like photosynthetic phenotype 1 (PGRL1) and the NADH dehydrogenase-like complex pathways are linked to the CET. Recently, the regulation of CET around photosystem I (PSI) has been recognized as crucial for photosynthesis and plant growth. Here, we summarized the main biochemical processes of the PGR5/PGRL1-dependent CET pathway and its physiological significance in protecting the photosystem II and PSI, ATP/NADPH ratio maintenance, and regulating the transitions between LET and CET in order to optimize photosynthesis when encountering unfavorable conditions. A better understanding of the PGR5/PGRL1-mediated CET during photosynthesis might provide novel strategies for improving crop yield in a world facing more extreme weather events with multiple stresses affecting the plants.
Highlights
Life on earth depends on energy derived from the sun
During the linear electron transport (LET), electrons derived from water splitting in photosystemPGR5/PGRL1-Dependent CETII (PSII) are transferred via the cytochrome (Cytb6f) complex, photosystem I (PSI) and ferredoxin (Fd) to the ferredoxin-NADP reductase (FNR), which reduce NADP+ to NADPH, resulting in the production of NADPH (Figure 1A; Lu et al, 2020)
The energy derived from LET and noncyclic photophosphorylation (NCPSP) plays an essential role in photosynthesis and other processes
Summary
Life on earth depends on energy derived from the sun. Photosynthesis is the pivotal process that could harvest light energy and generate biomass using water, CO2 and mineral nutrients. Plants have evolved several adaptations to cope with the unfavorable light situation: adjusting leaf orientation, ROS scavenging competence (Gill and Tuteja, 2010), xanthophyll cycle (Kuczynska et al, 2020), state transitions strategy (Hepworth et al, 2021), cyclic electron transport (CET; Yadav et al, 2020) and photorespiration (Storti et al, 2019). This review summarizes the main biochemical processes of PGR5/PGRL1-dependent CET pathway. The significance of the PGR5/PGRL1-dependent CET pathway is discussed to understand how plants optimize photosynthesis under unfavorable conditions by protecting the PSII and PSI, ATP/NADPH ratio maintenance, and regulating the transitions between linear electron transport (LET) and CET
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