Biology subjects

Tada, K.

Publications and source records attributed to Tada, K..

4 recordsLinked to original sources

bioRxiv2026

Two-step polar plastid migration via F-actin and microtubules ensures unequal inheritance during asymmetric division of Arabidopsis zygote

The zygote is the origin of development, and in most angiosperms, it divides asymmetrically to establish the apical-basal axis. In Arabidopsis thaliana, various organelles in the zygote undergo polar migration along actin filaments (F-actin), resulting in unequal inheritance, but the behavior of plastids, essential precursors of chloroplasts, has remained unclear. Here, using quantitative live-cell imaging, we reveal that plastids undergo two-step polar migration: they first move apically together with the nucleus along F-actin, and when nuclear migration slows, they switch to microtubule (MT)-dependent migration to move further apically. This results in unequal plastid inheritance by the apical cell. Although these plastids are amyloplasts containing starch granules, starch is dispensable for migration, unlike the gravity response. Instead, a fertilization-activated MAP kinase pathway is required for polar plastid migration. Our results demonstrate that the zygote possesses a spatiotemporal regulatory mechanism that ensures unequal plastid inheritance at the onset of plant ontogeny.

plant biology↗

bioRxiv2025

A simple and versatile plasma membrane staining method for visualizing living cell morphology in reproductive tissues across diverse plant species

Plant reproduction involves dynamic spatiotemporal changes that occur deep within maternal tissues. In ovules of Arabidopsis thaliana (A. thaliana), one of the two synergid cells degenerates at fertilization, while the fertilized egg cell (zygote) undergoes directional elongation followed by asymmetric division to initiate embryonic patterning. However, morphological analysis of these events has been hampered by the limitations of conventional cell wall staining, which fails to label cells lacking complete walls, and by the requirement for transgenic fluorescent reporters to visualize cell outlines. Here, we report that the membrane-specific fluorescent dye FM4-64 readily permeates ovules, allowing clear visualization of reproductive cell morphology both before and after fertilization. This staining method supports high-resolution time-lapse imaging and quantitative analysis of early embryogenesis in living tissues. Importantly, it is applicable not only to the angiosperm A. thaliana but also to the liverwort Marchantia polymorpha (M. polymorpha) and the fern Ceratopteris richardii (C. richardii), enabling the visualization of live reproductive cell structures within maternal tissues and revealing fertilization-associated morphological changes. This simple and robust method thus provides a valuable tool for spatiotemporal and quantitative analyses of reproductive processes across a broad range of plant species, without the need to generate transgenic lines.

plant biology↗

bioRxiv2025

Differential effects of the D1/S264V mutation in Photosystem II with either PsbA1 or PsbA3 on QB, non-heme Iron, and the associated hydrogen-bond network

The role of the D1/S264 residue and the role of its environment in the proton-coupled electron transfer reaction on the acceptor side of Photosystem II were investigated. To this end, D1/S264V mutants were constructed in the thermophilic cyanobacterium Thermosynechococcus elongatus, with D1 being either PsbA1 or PsbA3. The PSII mutants were investigated using EPR spectroscopy, thermoluminescence, (time-resolved) absorption changes measurements, and oximetry. While the mutation had minor effects in PsbA1-PSII, the S264V mutation in PsbA3-PSII had significant consequences: i) thermoluminescence data show inefficient electron transfer from QA- to QB; ii) re-oxidation of QA- was slowed, by at least a factor of 10; iii) the herbicides inhibit weakly O2 evolution; iv) no Fe2+QB- EPR signal was detected in dark-adapted PSII; instead, v) a large Fe3+ signal was present with vi) modified EPR properties; vii) no QA-Fe2+QB- biradical signal was observed after illumination at 198 K following a flash illumination, confirming the inefficient formation of QB-; viii) either no proton uptake coupled to non-heme iron reduction occurred or with a very slow rate compared to PsbA3-PSII; ix) changes were noted in the electrochromic response associated with QA- formation; and x) increased production of singlet oxygen, both with and without herbicides. The S264V mutation in PsbA3-PSII leads to a significant decrease in the energy gap between the QA-QB and QAQB- states. The effects listed above are discussed regarding the differences between PsbA1-PSII and PsbA3-PSII as those related to the sulfoquinovosyldiacylglycerol, the water molecules and the H-bond network.

biophysics↗

bioRxiv2024

Cysteine restriction induces ferroptosis depending on the polyamine biosynthetic pathway in hepatic cancer cells

Background and AimsMetabolic activities are also known to affect responses and disease processes of the liver which is a central organ for organismal metabolism. Liver diseases such as intestinal failure associated liver disease (IFALD) and hepatocellular carcinoma are known to be affected by nutrition contents, but the mechanisms behind them remain unclear. In this study, we aimed to reveal the relationship between the concentration of sulfur-containing amino acids and hepatocellular response, and further investigated the mechanism focusing on methionine adenosyltransferase (MAT), which plays the central role in methionine metabolism by synthesizing S-adenosylmethionine (SAM). MethodsMouse hepatoma Hepa1 cells were cultured in media with reduced amounts of cysteine, methionine, or both. Cell death was monitored using propidium iodide (PI) and annexin V staining followed by flow cytometry. Inhibitors of ferroptosis (Fer-1), autophagy (GSK872), SAM synthesis (cycloleucine), or polyamine synthesis (sardomozide and DFMO) were used. ResultsCysteine restriction induced marked cell death, whereas simultaneous restriction of cysteine and methionine fully suppressed the cell death. Cysteine restriction-induced cell death was suppressed with Fer-1 and GSK872, suggesting the involvement of ferroptosis in this process. Cysteine restriction-induced cell death was also suppressed by knockdown of MAT2A or its inhibitor cycloleucine. Furthermore, inhibitors of several enzymes in the polyamine biosynthetic pathway also suppressed the cell death. In contrast, primary culture of mouse hepatocytes did not show cell death upon cysteine restriction. ConclusionsThese results suggest that SAM-polyamine metabolism is a critical modulator of ferroptosis of hepatic cancer cells. Since normal liver cells were more resistant to ferroptosis than cancer cells, cysteine restriction may be exploited in treating hepatic cancer by inducing ferroptosis specifically in cancer cells without affecting normal cells in the liver. Graphical abstrct O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=61 SRC="FIGDIR/small/582667v1_ufig1.gif" ALT="Figure 1"> View larger version (13K): org.highwire.dtl.DTLVardef@bcb32borg.highwire.dtl.DTLVardef@96d39corg.highwire.dtl.DTLVardef@1eaa25org.highwire.dtl.DTLVardef@1346f82_HPS_FORMAT_FIGEXP M_FIG C_FIG

biochemistry↗