A New Light on Photosystem II Maintenance in Oxygenic Photosynthesis

Abstract

Life on earth is sustained by oxygenic photosynthesis, a process that converts solar energy, carbon dioxide, and water into chemical energy and biomass. Sunlight is essential for growth and productivity of photosynthetic organisms. However, exposure to an excessive amount of light adversely affects fitness due to photooxidative damage to the photosynthetic machinery, primarily to the reaction center of the oxygen-evolving photosystem II (PSII). Photosynthetic organisms have evolved diverse photoprotective and adaptive strategies to avoid, alleviate, and repair PSII damage caused by high-irradiance or fluctuating light. Rapid and harmless dissipation of excess absorbed light within antenna as heat, which is measured by chlorophyll fluorescence as non-photochemical quenching (NPQ), constitutes one of the most efficient protective strategies. In parallel, an elaborate repair system represents another efficient strategy to maintain PSII reaction centers in active states. This article reviews both the reaction center-based strategy for robust repair of photodamaged PSII and the antenna-based strategy for swift control of PSII light-harvesting (NPQ). We discuss evolutionarily and mechanistically diverse strategies used by photosynthetic organisms to maintain PSII function for growth and productivity under static high-irradiance light or fluctuating light environments. Knowledge of mechanisms underlying PSII maintenance would facilitate bioengineering photosynthesis to enhance agricultural productivity and sustainability to feed a growing world population amidst climate change.

Early Identification of Herbicide Modes of Action by the Use of Chlorophyll Fluorescence Measurements

“…F O is the fluorescence level when Q A is oxidized, and it may change when exposed to stress [38]. An increase in F O indicates a decrease in the rate constant of energy trapped by PSII reaction centers [39], which may be the result of damage to PSII core unit, observed in several previous studies [40]. The increase of F O was also reported to be related to an accumulation of reduced plastoquinone (PQ).…”

A Brassica napus Reductase Gene Dissected by Associative Transcriptomics Enhances Plant Adaption to Freezing Stress

“…Abiotic stresses lead to photoinhibition as well as excessive generation of ROS, which suppresses the photosynthetic progress and ultimately repress the growth and productivity in plants ( Gabriel et al., 2010 ; Nishiyama et al., 2014 ). During the long-term evolution, plants have developed a variety of adaptive mechanisms to cope with the stressful conditions ( Liu et al., 2019a ; Strzepek et al., 2019 ). The CBF transcription factors in rapeseed are known to be responsible for the photosynthetic performance; CBF5 and CBF17 enhance the energy conversion efficiency under LT conditions ( Savitch et al., 2005 ; Dahal et al., 2012 ).…”

“…However, it is unclear whether HSPs function similarly in rapeseed to alleviate injury from LT stress. The other observations have mechanistically described how the photosynthetic organisms maintain their PSII function under stressful conditions with continuing or fluctuating light (Liu et al, 2019a). For instance, the chloroplast protein HHL1 forms a complex with LQY1 to repair and re-assemble PSII, which in turn helps overcome excessive light stress (Jin et al, 2014).…”

Emerging Molecular Links Between Plant Photomorphogenesis and Virus Resistance

“…Light is a critical environmental factor for both plant growth ( Wang et al, 2019 ) and virus infection ( Paudel and Sanfaçon, 2018 ). On the plant side, light is the major environmental input for photosynthesis ( Liu et al, 2019 ) as well as photomorphogenesis ( Montgomery, 2016 ). Photomorphogenesis refers to a series of morphological changes in plant development when dark-grown seedlings are exposed to light ( Paik and Huq, 2019 ).…”