Biology subjects

Ikeuchi, M.

Publications and source records attributed to Ikeuchi, M..

5 recordsLinked to original sources

bioRxiv2026

VLCFA-mediated inter-cell layer communication controls cellular pluripotency in Arabidopsis callus

Plants have remarkable capacity to reconstruct entire organ systems from tissue explants. In Arabidopsis two-step tissue culture system, pluripotency regulators are specifically expressed in the middle-cell layer of the stratified callus tissue. However, regulatory mechanisms underlying the radial patterning of callus remained unclear. Here, we found that very-long-chain fatty acids (VLCFAs) synthesized in the epidermis-like outermost layer are essential for pluripotency acquisition and successful shoot regeneration. Our genetic and transcriptomic analyses revealed that the regulatory roles of VLCFAs on pluripotency acquisition involve inter-cell layer signaling in callus tissue, while they are at least partly independent of ATML1/PDF2 functions and cuticular wax synthesis in the outermost layer. VLCFAs spatially restrict procambium cell identity by non-cell-autonomously suppressing cytokinin signaling, thereby allowing for establishment of the middle-cell layer. We propose that the inhibitory relationships between layer-specific regulators underlie the intricate balance of cellular fate determination in pluripotent callus.

plant biology↗

bioRxiv2025

Wounding activates the HSFA1 transcription factors to promote cellular reprogramming in Arabidopsis

Mechanical injury is a primary trigger for cellular reprogramming during organ regeneration, yet the molecular mechanisms that link wounding to reprogramming remain poorly understood. In this study we identify the Arabidopsis HEAT SHOCK FACTOR A1 (HSFA1) class of transcription factors, being key regulators of the heat stress response, as central players in wound-induced callus formation and shoot regeneration. Loss of HSFA1 function in the hsfa1abd triple mutants severely impairs cellular reprogramming, reducing callus formation from wounded hypocotyls, as well as shoot regeneration from explants. Conversely, overexpression of the HSFA1d gain-of-function variant markedly enhances regeneration. Time-series RNA-seq and ChIP-seq analyses revealed that HSFA1s directly activate the key reprogramming regulators WOUND-INDUCED DEDIFFERENTIATION 1 (WIND1), PLETHORA 3 (PLT3) and ZINC FINGER OF ARABIDOPSIS THALIANA 6 (ZAT6). Furthermore, we demonstrate that HSFA1d activity is attenuated by SIZ1-mediated SUMOylation, linking post-translational modification to the regulation of wound responses. Our findings establish HSFA1s as an early transcriptional hub that integrates wound signals with the activation of a broad gene network that drives cellular reprogramming, thereby providing a mechanistic framework for understanding how stress-responsive transcription factors control regeneration.

plant biology↗

bioRxiv2024

Functional Modification of Cyanobacterial Phycobiliprotein and Phycobilisomes through Bilin Metabolism Control

The light-harvesting antenna complexes in cyanobacteria are known as phycobilisomes (PBSs), and they can adapt to a diverse range of light environments owing to the deployment of different phycobiliproteins within the PBS structures. Freshwater cyanobacteria such as Synechococcus elongatus PCC 7942 thrive under red light due to phycocyanin (PC), along with phycocyanobilin (PCB), in PBS. Conversely, cyanobacteria in shorter-wavelength light environments, such as green light, employ phycoerythrin paired with phycoerythrobilin (PEB) alongside PC in PBS. Synthetic biology studies have shown that PEB production can be enhanced by additional expression of the heterologous PEB synthases, namely 15,16-dihydrobiliverdin:ferredoxin oxidoreductase and PEB:ferredoxin oxidoreductase (PebAB), leading to cellular browning due to PEB accumulation. This approach is genetically unstable, and the properties of the resulting PEB-bound PBS complexes remain uncharacterized. Herein, we engineered a novel strain of Synechococcus 7942 PEB1, with finely tuned control of PEB metabolism. PEB1 exhibited a remarkable and reversible color shift from green to brown and pink, based on the PebAB induction levels. High induction led to a complete PCB-to-PEB substitution, causing the disassembly of the PBS rod complex. In contrast, low PebAB levels resulted in the formation of a stable chimeric PBS complex with partial PCB-to-PEB substitution. This adaptation enabled efficient light harvesting in the green spectrum and energy transfer to the photosynthetic reaction center. These findings, which improve our understanding of PBS and highlight the structural importance of the bilin composition, lay the foundation for future PBS adaptation studies in bioengineering, synthetic biology, and renewable energy.

synthetic biology↗

bioRxiv2021

Biosynthesis system of Synechan, a sulfated exopolysaccharide, in the model cyanobacterium Synechocystis sp. PCC 6803

Extracellular polysaccharides of bacteria contribute to biofilm formation, stress tolerance, and infectivity. Cyanobacteria, the oxygenic photoautotrophic bacteria, uniquely and widely have sulfated extracellular polysaccharides and they may utilize the polysaccharides for survival in nature. In addition, sulfated polysaccharides of cyanobacteria and other organisms have been focused as beneficial biomaterial. However, very little is known about their biosynthesis machinery and function in cyanobacteria. Here we found that the model cyanobacterium, Synechocystis sp. PCC 6803, formed bloom-like cell aggregates using sulfated extracellular polysaccharides (designated as synechan) and identified whole set of genes responsible for synechan biosynthesis and its transcriptional regulation, thereby suggesting a model for the synechan biosynthesis apparatus. Because similar genes are found in many cyanobacterial genomes with wide variation, our findings may lead elucidation of various sulfated polysaccharides, their functions, and their potential application in biotechnology.

microbiology↗

bioRxiv2019

Blue/green light-responsive cyanobacteriochromes are cell shade sensors in red light-replete niches

Photoautotrophic cyanobacteria have developed sophisticated light response systems to capture and utilize the energy and information of incident light [1]. Cyanobacteria-specific photoreceptors cyanobacteriochromes (CBCRs) are distantly related to more widespread phytochromes. CBCRs show the most diverse spectral properties among the naturally occurring photoreceptors, typified by a unique and prevailing blue/green light-absorbing variant [2-6]. However, where the CBCR-mediated colorful signaling systems function in nature has been elusive. We previously reported that the three CBCRs SesA/B/C synthesize/degrade a bacterial second messenger cyclic diguanylate (c-di-GMP) in response to blue/green light [6-8]. The cooperative action of SesA/B/C enables blue light-ON and green light-OFF regulation of the c-di-GMP-dependent cell aggregation of the thermophilic cyanobacterium Thermosynechococcus vulcanus [8, 9]. Here, we report that SesA/B/C can serve as a physiological sensor of cell density. Because cyanobacterial cells show lower transmittance of blue light than green light, higher cell density gives more green light-enriched irradiance to cells. The cell density-dependent suppression of cell aggregation under blue/green-mixed light and white light conditions support this idea. Such a sensing mechanism may provide information about the cell position in cyanobacterial mats in hot springs, the natural habitat of Thermosynechococcus. This cell position-dependent SesA/B/C-mediated regulation of cellular sessility (aggregation) might be ecophysiologically essential for the reorganization and growth of phototrophic mats. We also report that the green light-induced dispersion of cell aggregates requires red light-driven photosynthesis. Blue/green CBCRs might work as shade detectors in a different niche than red/far-red phytochromes, which may be why CBCRs have evolved in cyanobacteria.

microbiology↗