Biology subjects

Nix, S. J.

Publications and source records attributed to Nix, S. J..

3 recordsLinked to original sources

bioRxiv2026

PsbS confers limited adaptive benefit to C4 photosynthesis under fluctuating light

Adaptation of plant photosynthesis to dynamic light conditions experienced in natural environments is achieved through specific protective mechanisms. Energy-dependent non-photochemical quenching (qE), regulated by Photosystem II Subunit S (PsbS), is a key process facilitating acclimation to fluctuating light in C3 plants, which operate conventional photosynthesis. C4 plants, which include some of the worlds most productive and agriculturally important crops, have evolved a distinct high-efficiency photosynthetic pathway. Little is known about the role of specific processes, like qE, in acclimation of C4 plants to dynamic light environments. We generated gene-edited lines of the model C4 grass Setaria viridis lacking PsbS, which were found to be deficient in qE. This deficiency resulted in a modest increase in PSII photoinhibition and a CO2 assimilation penalty under light stress in short-term experiments, but photosynthesis and growth under fluctuating light were unaffected. Instead, keeping Photosystem I oxidised through photosynthetic control, negative feedback regulation of the Cytochrome b6f complex, was critical. Therefore, unlike in C3 plants, qE does not provide a significant adaptive advantage to C4 plants under dynamic light conditions. These findings provide important insights into the biology of C4 plants and help prioritise future strategies for improving the productivity and resilience of C4 crops.

plant biology↗

bioRxiv2024

A novel PGRL1 paralog refined the control of photoprotection in grasses and facilitated cell specialisation in C4 photosynthesis

The PGR5-PGRL1 pathway protects plants from photodamage by regulating electron flow to maintain Photosystem I in an oxidised state. Grasses possess two PGRL1 paralogs, but their functional roles have remained unknown. Here, we show that the ancestral PGRL1 paralog, PGRL1, which is conserved across algae and land plants, is enriched in the mesophyll cells of grasses that perform the NADP-ME subtype of C4 photosynthesis. In contrast, the grass-specific paralog PGRL1{beta} is enriched in bundle sheath cells. To investigate the functional significance of this cell-specific expression, we generated gene-edited lines of the NADP-ME C4 grass Setaria viridis lacking either PGRL1 paralog. We found that PGRL1{beta} in bundle sheath cells was required for rapid photoprotection, enabling Photosystem I oxidation five seconds faster during transitions from darkness to high light. In contrast, PGRL1 in mesophyll cells was essential for maintaining Photosystem I oxidation under steady-state high-light conditions. We propose that these complementary functions arise from structural differences within the lumen-facing regions of the two paralogs, providing a mechanistic basis for their distinct roles in regulating photoprotection. The conservation of this dual PGRL1 system across grasses suggests that functional specialisation of the paralogs expands the dynamic range of protective responses, enhancing photosynthetic performance under fluctuating and high-light stress conditions.

plant biology↗

bioRxiv2024

PGR5 promotes energy-dependent non-photochemical quenching to enable efficient C4 photosynthesis under fluctuating light

PROTON GRADIENT REGULATION 5 (PGR5) is essential for generating proton motive force across thylakoid membranes in C3 plants and supporting photoprotection under fluctuating light conditions. It is proposed that this function is achieved by regulating cyclic electron flow around Photosystem I. During the evolutionary transition from C3 to C4 photosynthesis, the leaf abundance of PGR5 has increased, coinciding with a rise in the cyclic electron flow rate. To investigate the contribution of PGR5 to photoprotection in C4 photosynthesis, we generated model C4 monocot Setaria viridis with null pgr5 alleles. We show that plants lacking PGR5 struggle to establish proton motive force and energy-dependent non-photochemical quenching (qE) at higher irradiances during instantaneous measurements. This leads to a progressive decline in maximum Photosystem I activity when leaves are exposed to repeated cycles of high irradiance. Additionally, plants without PGR5 exhibit severely reduced growth and photosynthesis compared to wild type plants when grown under fluctuating daylight but not under constant daylight. In the absence of PGR5, a slower-relaxing, zeaxanthin-dependent form of non-photochemical quenching supports growth under fluctuating light, albeit at the cost of reduced photochemical efficiency and assimilation rate. Our findings underscore the role of PGR5 in enabling efficient C4 photosynthesis under fluctuating light by establishing proton motive force for the rapid upregulation of qE and preventing photodamage to the electron transport machinery. This study highlights the importance of various non-photochemical quenching mechanisms for C4 photosynthesis and emphasises the role of PGR5 in the evolution of C4 plants.

plant biology↗