Biology subjects

Hisabori, T.

Publications and source records attributed to Hisabori, T..

3 recordsLinked to original sources

bioRxiv2026

PIFI Stabilizes Chloroplast NDH-PSI Supercomplex to Maintain Plastoquinone Redox Balance and PSII Efficiency

Photosynthetic electron transport is mediated by several protein supercomplexes that are spatially arranged in the thylakoid membranes of chloroplasts. The chloroplast NADH dehydrogenase-like (NDH) complex is part of the photosynthetic alternative electron transport (AET) chain, which reduces the plastoquinone (PQ) pool using reduced ferredoxin as a substrate. This NDH complex is associated with photosystem I (PSI) and mediates a portion of AET in stroma lamellae, whereas photosystem II (PSII) is concentrated in grana stacks. This study presents the findings regarding post-illumination chlorophyll fluorescence increase (PIFI), a protein crucial for regulating AET via the NDH pathway. A marked increase in NDH activity and a reduction in the PQ pool in the dark were observed in PIFI-deficient mutant strains (g-pifi) generated by genome editing. Blue native PAGE analysis indicated that PIFI was associated with the NDH-PSI supercomplex in the wild type, and the NDH complex was dissociated from PSI in the g-pifi mutants. Additionally, the g-pifi mutants exhibited a decrease in the maximum quantum yield of PSII (Fv/Fm). Notably, Fv/Fm was restored in a double mutant harboring both g-pifi and NDH-deficient pnsl1 mutations, demonstrating that deregulated NDH activity in g-pifi causes downregulation of PSII efficiency. However, the lower Fv/Fm was not observed in a mutant lacking thioredoxin m4 (trxm4), which showed deregulated NDH activity but maintained the NDH-PSI supercomplex. These data suggest that PIFI stabilizes the NDH-PSI supercomplex and maintains the spatial localization of PQ reduction via AET in thylakoid membranes, which is essential for the proper functioning of PSII.

plant biology↗

bioRxiv2024

SOQ1 functions as a methionine sulfoxide reductase in the chloroplast lumen for regulation of photoprotective qH in Arabidopsis

Photosynthetic organisms must balance light absorption and energy dissipation to prevent photo-oxidative damage. Non-photochemical quenching (NPQ) dissipates excess light energy as heat, with the quenching component qH providing sustained photoprotection. However, the molecular mechanism underlying qH induction remains unclear. Our study focuses on the thylakoid membrane protein SUPPRESSOR OF QUENCHING 1 (SOQ1) and its inhibition of qH through interaction with LIPOCALIN IN THE PLASTID (LCNP) in Arabidopsis thaliana. Structural homology of SOQ1 lumenal domains with bacterial disulfide bond protein D suggested potential thiol-disulfide exchange activity. In vitro assays determined that both SOQ1 thioredoxin-like (Trx-like) and C-terminal (CTD) domains contain a redox-active cysteine pair and evidenced electron transfer from Trx-like to CTD. Importantly, we found that SOQ1 lumenal domains exhibit methionine sulfoxide reductase (Msr) activity converting oxidized methionine residues in LCNP back to methionine, which thereby inactivates LCNP and prevents qH formation. Mutational analyses identified cysteine residues in SOQ1-CTD and methionine residues in LCNP as critical for qH suppression, supporting their role in redox regulation. Additionally, we found that the redox state of SOQ1 in vivo is light-dependent, shifting from reduced to oxidized under stress conditions, indicating a dynamic regulation of its activity. We conclude that the Trx-like domain of SOQ1 provides reducing power to its CTD displaying Msr activity. SOQ1 is therefore an unusual example of a protein possessing both a disulfide reductase and Msr domain in tandem. Our findings elucidate the redox-regulation mechanism of qH involving SOQ1-mediated methionine reduction of LCNP, providing insights into the intricate control of photoprotective processes in chloroplasts and enhancing our understanding of plant resilience under environmental stress.

plant biology↗

bioRxiv2020

Basis for the phototaxis sign reversal in the green alga Chlamydomonas reinhardtii studied by high-speed observation

For organisms that respond to environmental stimuli using taxes, reversal of the tactic sign should be tightly regulated for survival. The biciliate green alga Chlamydomonas reinhardtii is an excellent model for studying reversal between positive and negative phototaxis. C. reinhardtii cells change swimming direction by modulating the balance of beating forces between their two cilia after photoreception at the eyespot; however, it remains unknown how they reverse phototactic sign. In this study, we observed cells undergoing phototactic turns with a high-speed camera and found that two key factors determine the phototactic sign: which of the two cilia beats more strongly for phototactic turning and when the strong beating starts. The timing of the strong ciliary beating is suggested to be regulated by ROS-regulated switching between the light-on and light-off responses at the eyespot, which leads to the switching between positive and negative phototaxis. This idea is supported by a mathematical model that introduces the timing of the strong ciliary beating after photoreception.

cell biology↗