Springer Science and Business Media LLC Acta Medica Okayama 0918-9440 139 2 2026 Knockout of a single aquaporin, OsPIP2;4, decreases root water permeability in rice 255 265 EN Aya Onishi Institute of Plant Science and Resources, Okayama University Tomoaki Horie Division of Applied Biology, Faculty of Textile Science and Technology, Shinshu University Ryo Ishitsuka Institute of Plant Science and Resources, Okayama University Shizuka Sasano Institute of Plant Science and Resources, Okayama University Rie Horie Division of Applied Biology, Faculty of Textile Science and Technology, Shinshu University Yunosuke Mito Division of Applied Biology, Faculty of Textile Science and Technology, Shinshu University Shigeko Utsugi Institute of Plant Science and Resources, Okayama University Junko Ishikawa Institute of Crop Science, NARO Majid Mahdieh Institute of Plant Science and Resources, Okayama University Maki Katsuhara Institute of Plant Science and Resources, Okayama University Aquaporins (AQPs) are membrane proteins that facilitate water transport and are present in nearly all bacterial, animal, and plant cells. In plants, AQPs are classified into four or more subfamilies, with plasma membrane intrinsic proteins (PIPs) playing a key role in root water uptake and cellular water regulation. Previous studies have demonstrated that PIPs contribute to root hydraulic conductivity (Lpr) in various plant species. In this study, we examined the specific role of OsPIP2;4, one of the PIP-type aquaporins among 11 rice (Oryza sativa) PIP2s, in regulating Lpr. Transgenic rice plants, including OsPIP2;4-knockout (KO) and overexpressing (Ox) lines, were used for this investigation. Two independent KO lines, generated via the CRISPR-Cas9 system and T-DNA insertion mutagenesis, respectively, showed significantly lower Lpr compared to wild-type rice plants. The decrease in Lpr in the T-DNA KO line was associated with reduced OsPIP2;4 transcript levels, measured by real-time PCR, and lower OsPIP2;4 protein levels, as shown by immunohistochemical analysis. Conversely, no notable increase in Lpr was observed in the Ox lines. These results suggest that OsPIP2;4 is expressed in appropriate tissues in rice roots and is a key factor influencing Lpr. This research represents a significant step toward further understanding the physiological functions of OsPIP2;4 in rice. No potential conflict of interest relevant to this article was reported.

Wiley Acta Medica Okayama 0140-7791 2025 Amino Acid Substitutions in Loop C of Arabidopsis PIP2 Aquaporins Alters the Permeability of CO2 EN Shaila Shermin Tania Institute of Plant Science and Resources, Okayama University Shigeko Utsugi Institute of Plant Science and Resources, Okayama University Yoshiyuki Tsuchiya Institute of Plant Science and Resources, Okayama University Shizuka Sasano Institute of Plant Science and Resources, Okayama University Maki Katsuhara Institute of Plant Science and Resources, Okayama University Izumi C. Mori Institute of Plant Science and Resources, Okayama University The transport of CO2 across biomembranes in plant cells is essential for efficient photosynthesis. Some aquaporins capable of CO2 transport, referred to as ‘COOporins’, are postulated to play a crucial role in leaf CO2 diffusion. However, the structural basis of CO2 permeation through aquaporins remains largely unknown. Here, we show that amino acids in loop C are critical for the CO2 permeability of Arabidopsis thaliana PIP2 aquaporins. We found that swapping tyrosine and serine in loop C to histidine and phenylalanine, which differ between AtPIP2;1 and AtPIP2;3, altered CO2 permeability when examined in the Xenopus laevis oocyte heterologous expression system. AlphaFold2 modelling indicated that these substitution induced a conformational shift in the sidechain of arginine in the aromatic/arginine (ar/R) selectivity filter and in lysine at the extracellular mouth of the monomeric pore in PIP2 aquaporins. Our findings demonstrate that distal amino acid substitutions can trigger conformational changes of the ar/R filter in the monomeric pore, modulating CO2 permeability. Additionally, phylogenetic analysis suggested that aquaporins capable of dual water/CO2 permeability are ancestral to those that are water-selective and CO2-impermeable, and CO2-selective and water impermeable. No potential conflict of interest relevant to this article was reported.

Elsevier BV Acta Medica Okayama 0981-9428 227 2025 The hidden cation-selective pore in ion-conducting aquaporin OsPIP2;4 from rice 110168 EN Shuntaro Ono Institute of Plant Science and Resources, Okayama University Sen Thi Huong Tran Institute of Plant Science and Resources, Okayama University Yasunori Saitoh Research Institute for Interdisciplinary Science, Okayama University Shigeko Utsugi Institute of Plant Science and Resources, Okayama University Tomoaki Horie Division of Applied Biology, Faculty of Textile Science and Technology, Shinshu University Maki Katsuhara Institute of Plant Science and Resources, Okayama University Ion-conducting aquaporins (icAQPs) transport ions as well as water. Although the molecular mechanism of how AQPs establish selective permeability for water molecules is well understood, the ion-transporting mechanism in icAQPs has not yet been fully elucidated. In this study, we investigated the molecular mechanism of cation transport in OsPIP2;4, an icAQP in rice, by homology modeling and the electrophysiological analysis using Xenopus laevis oocytes. Water and ion transport assays using OsPIP2;4 T227M and G278K mutants strongly suggested that water- and cation-transporting pathways are independent of each other. Data from amino acid substitutions V54I and A143G in OsPIP2;4 led to the identification of a novel hidden pathway for cation transport located on the side surfaces of the tetramer channel, where two protomers are in contact, which is distinct from conventional monomeric pores and the tetrameric central pore in AQPs. Moreover, the present results provide the possibility that this hypothetical hidden pore also functions in the barley icAQP HvPIP2;8. The overall structure of this novel pathway appears to differ from the structure of general cation channels. However, the arrangement of hydrophilic amino acids at the entrance of the pathway of OsPIP2;4 was found to be comparable to that of some cation channels, which implies that the molecular mechanism of dehydration of hydrated ions might resemble that of the channels. Although direct structural evidence is needed to confirm the proposed pathway, the present study can be a stepping stone toward unraveling the mechanism of dual water and ion transport through icAQPs in plants. No potential conflict of interest relevant to this article was reported.

Acta Medica Okayama 1559-2316 7 12 2012 Functional characterization of a novel plasma membrane intrinsic protein2 in barley 1842 1846 EN Mineo Shibasaka Sizuka Sasano Sigeko Utsugi Maki Katsuhara Water homeostasis is crucial to the growth and survival of plants. Plasma membrane intrinsic proteins (PIPs) have been shown to be primary channels mediating water uptake in plant cells. We characterized a novel PIP2 gene, HvPIP2;8 in barley (Hordeum vulgare). HvPIP2;8 shared 72–76% identity with other HvPIP2s and 74% identity with rice OsPIP2;8. The gene was expressed in all organs including the shoots, roots and pistil at a similar level. When HvPIP2;8 was transiently expressed in onion epidermal cells, it was localized to the plasma membrane. HvPIP2;8 showed transport activity for water in Xenopus oocytes, however its interaction with HvPIP1;2 was not observed. These results suggest that HvPIP2;8 plays a role in water homeostasis although further functional analysis is required in future. No potential conflict of interest relevant to this article was reported.

岡山大学環境管理センター Acta Medica Okayama 0917-1533 31 2009 岡山大学資源生物科学研究所における屋上緑化による建物冷却効果 21 25 EN Maki Katsuhara Shigemi Tanakamaru Izumi C. Mori Akio Tani Shigeko Utsugi Takashi Enomoto Toshihiko Maitani Roof greening is known to be environmentally friendly technology. Recently developed new roof greening systems, such as the thin-layer/Excel soil© system and the wetland type greening system, were tested at the roof top of buildings of Research Institute for Bioresources, Okayama University. After a multi-year test, these new systems have been established during high-temperature and less-rainfall summer seasons in the south Okayama region. Data indicated that roof greening effectively reduced the temperature of the concrete surface (more than 10°C). The room temperature under the green roof was also reduced both in a stock room (up to 6°C) and in an office room (about 2°C). We also provided the estimation indicating that this roof greening is useful for the decrease in CO(2) emission through the reduction of the electric power for air-conditioning in the summer. No potential conflict of interest relevant to this article was reported.

Acta Medica Okayama 1998 MOLECULAR BIOLOGICAL STUDY ON FLOWER-SPECIFIC GENES IN ARABIDOPSIS THALIANA EN No potential conflict of interest relevant to this article was reported.