Biology subjects

Sakamoto, W.

Publications and source records attributed to Sakamoto, W..

4 recordsLinked to original sources

bioRxiv2025

Chloroplast cpHsc70-1 interacts with VIPP1 C-terminal tail and controls VIPP1 oligomer disassembly in thylakoid membrane remodeling

Oxygenic photosynthetic organisms depend on the thylakoid membranes (TMs) for light-driven energy conversion. Recent studies on TM homeostasis (thylakostasis) have highlighted the essential role of the TM remodeling protein VIPP1 (Vesicle Inducing Protein in Plastids 1). As a member of the ESCRT-III/PspA/VIPP1 superfamily, VIPP1 forms large ring- and filament-like homo-oligomeric structures that exhibit a membrane remodeling activity. The oligomerization status was proposed to be modulated by the intrinsically disordered C-terminal tail (Vc), whereas its functional role remained unclear. Notably, this Vc region is conserved not only in photosynthetic VIPP1 but also in the PspA proteins of extremophilic species, implicating its role in membrane stress responses. To investigate the role of the Vc region in VIPP1 assembly, we performed co-immunoprecipitation assays in Arabidopsis chloroplasts and identified chloroplast-localized HSP70 proteins as major interactors. Among the two isoforms, cpHsc70-1 was found to be specifically required for modulating VIPP1 oligomeric assembly and dynamics in response to heat stress. Genetic analyses revealed that cpHsc70-1 facilitates the disassembly of VIPP1 oligomers, similarly to Vps4 ATPase in ESCRT-III; loss of either the Vc region or cpHsc70-1 impaired VIPP1 disassembly, resulting in more static oligomeric structures. Furthermore, cpHsc70-1 exhibited a broader role in chloroplast proteostasis, as the cphsc70-1 mutant showed impaired accumulation of GFP-fusion proteins. Together, our findings uncover a crucial crosstalk between proteostasis and thylakostasis in chloroplasts, coordinated by cpHsc70-1 and VIPP1 in response to membrane stress. Significance StatementOrganisms performing oxygen-evolving photosynthesis rely on the thylakoid membranes (TMs) for light-driven energy conversion. We reveal that VIPP1, a membrane remodeling protein forming dynamic oligomeric structures, is crucial for TM maintenance. Its intrinsically disordered C-terminal region (Vc) and the heat shock protein cpHsc70-1 coordinate VIPP1 disassembly during stress in Arabidopsis chloroplasts. Loss of either component causes defects in membrane remodeling and proteostasis. Our findings uncover a fundamental mechanism connecting membrane integrity and protein quality control, ensuring chloroplast resilience against environmental stress.

plant biology↗

bioRxiv2023

Characterization of Tryptophan Oxidation Affecting D1 Degradation by FtsH in the Photosystem II Quality Control of Chloroplasts

Photosynthesis is one of the most important reactions for sustaining our environment. Photosystem II (PSII) is the initial site of photosynthetic electron transfer by water oxidation. Light in excess, however, causes the simultaneous production of reactive oxygen species (ROS), leading to photo-oxidative damage in PSII. To maintain photosynthetic activity, the PSII reaction center protein D1, which is the primary target of unavoidable photo-oxidative damage, is efficiently degraded by FtsH protease. In PSII subunits, photo-oxidative modifications of several amino acids such as Trp have been indeed documented, whereas the linkage between such modifications and D1 degradation remains elusive. Here, we show that an oxidative post-translational modification of Trp residue at the N-terminal tail of D1 is correlated with D1 degradation by FtsH during high-light stress. We revealed that Arabidopsis mutant lacking FtsH2 had increased levels of oxidative Trp residues in D1, among which an N-terminal Trp-14 was distinctively localized in the stromal side. Further characterization of Trp-14 using chloroplast transformation in Chlamydomonas indicated that substitution of D1 Trp-14 to Phe, mimicking Trp oxidation enhanced FtsH-mediated D1 degradation under high light, although the substitution did not affect protein stability and PSII activity. Molecular dynamics simulation of PSII implies that both Trp-14 oxidation and Phe substitution cause fluctuation of D1 N-terminal tail. Furthermore, Trp-14 to Phe modification appeared to have an additive effect in the interaction between FtsH and PSII core in vivo. Together, our results suggest that the Trp oxidation at its N-terminus of D1 may be one of the key oxidations in the PSII repair, leading to processive degradation by FtsH. Competing Interest StatementThe authors have no conflict of interest, financial or otherwise, in relation to this study Impact StatementOxidative modification of Tryptophan residues in the reaction center protein D1 may be a key to drive the Photosystem II repair, likely enhancing accessibility of FtsH protease to D1.

plant biology↗

bioRxiv2021

Dominant Awn Inhibitor, which encodes an ALOG protein in sorghum, suppresses awn formation in rice

The awn, a needle-like structure extending from the tip of the lemma in grass species, plays a role in environmental adaptation and fitness. In some crops, awns appear to have been eliminated during domestication. Although numerous genes involved in awn development have been identified, several dominant genes that eliminate awns are also known to exist. For example, in sorghum (Sorghum bicolor), the dominant awn inhibiting gene has been known since 1921; however, its molecular features remain uncharacterized. In this study, we conducted quantitative trait locus analysis and a genome-wide association study of awn-related traits in sorghum and identified DOMINANT AWN INHIBITOR (DAI), which encodes the ALOG family protein on chromosome 3. DAI appeared to be present in most awnless sorghum cultivars, likely because of its effectiveness. Detailed analysis of the ALOG protein family in cereals revealed that DAI originated from duplication of its twin paralog (DAIori) on chromosome 10. Observations of immature awns in near-isogenic lines revealed that DAI inhibits awn elongation by suppressing both cell proliferation and elongation. We also found that only DAI gained a novel function to inhibit awn elongation through an awn-specific expression pattern distinct from that of DAIori. Interestingly, heterologous expression of DAI with its own promoter in rice inhibited awn elongation in the awned cultivar Kasalath. We found that DAI originated from gene duplication, providing an interesting example of gain-of-function that occurs only in sorghum but shares its functionality with rice and sorghum.

plant biology↗

bioRxiv2020

Structural basis for VIPP1 oligomerization and maintenance of thylakoid membrane integrity

Vesicle-inducing protein in plastids (VIPP1) is essential for the biogenesis and maintenance of thylakoid membranes, which transform light into life. However, it is unknown how VIPP1 performs its vital membrane-shaping function. Here, we use cryo-electron microscopy to determine structures of cyanobacterial VIPP1 rings, revealing how VIPP1 monomers flex and interweave to form basket-like assemblies of different symmetries. Three VIPP1 monomers together coordinate a non-canonical nucleotide binding pocket that is required for VIPP1 oligomerization. Inside the rings lumen, amphipathic helices from each monomer align to form large hydrophobic columns, enabling VIPP1 to bind and curve membranes. In vivo point mutations in these hydrophobic surfaces cause extreme thylakoid swelling under high light, indicating an essential role of VIPP1 lipid binding in resisting stress-induced damage. Our study provides a structural basis for understanding how the oligomerization of VIPP1 drives the biogenesis of thylakoid membranes and protects these life-giving membranes from environmental stress.

plant biology↗