Biology subjects

Ehira, S.

Publications and source records attributed to Ehira, S..

5 recordsLinked to original sources

bioRxiv2026

A phosphorylation-dependent partner-switching-like module controls heterocyst polysaccharide layer formation in Anabaena sp. strain PCC 7120

Heterocysts are specialized cells formed by filamentous cyanobacteria to enable nitrogen fixation under aerobic conditions. These cells are surrounded by a multilayered envelope, including a heterocyst-specific polysaccharide (Hep) layer that restricts oxygen diffusion and protects nitrogenase activity. Although several genes required for Hep biosynthesis have been identified, the regulatory mechanisms controlling Hep layer formation remain poorly understood. Here, we show that Hep layer formation in Anabaena sp. PCC 7120 is regulated by a phosphorylation-dependent partner-switching-like system. The phosphatase HenR and the STAS domain-containing protein All4160 are both required for Hep formation and nitrogen fixation. A nonphosphorylatable All4160 variant restores Hep formation and nitrogen fixation in a henR disruptant, indicating that phosphorylation negatively regulates All4160 function. Using a bacterial two-hybrid assay, we identified two candidate kinases, Alr3423 and All2284, that interact with All4160, and both proteins phosphorylate All4160 in vitro. Genetic analysis revealed that deletion of alr3423, but not all2284, suppresses the nitrogen fixation defect of the henR disruptant, suggesting that Alr3423 is a major kinase regulating All4160 in vivo. These findings uncover a phosphorylation switch that controls heterocyst polysaccharide layer formation and expand the role of partner-switching systems beyond {sigma} factor-dependent transcription to the direct regulation of a biosynthetic enzyme involved in exopolysaccharide (EPS) synthesis. ImportanceExopolysaccharides (EPS) are involved in diverse aspects of bacterial physiology, including environmental acclimation, motility, host association, and cellular differentiation, yet their regulatory mechanisms remain poorly understood. Cyanobacteria play central roles in global carbon and nitrogen cycles through photosynthesis and nitrogen fixation, the latter requiring a micro-oxic environment provided by specialized cells called heterocysts. This study reveals a previously unrecognized mechanism for controlling polysaccharide biosynthesis, in which a partner-switching-like system directly regulates the activity of a biosynthetic enzyme. By expanding the role of partner-switching systems beyond {sigma} factor-dependent transcription, these findings provide a framework for understanding how bacteria control EPS production in response to environmental and developmental cues.

microbiology↗

bioRxiv2022

Structure of a monomeric photosystem I core associated with iron-stress-induced-A proteins from Anabaena sp. PCC 7120

Iron-stress-induced-A proteins (IsiAs) are expressed in cyanobacteria under iron-deficient conditions. The cyanobacterium Anabaena sp. PCC 7120 has four isiA genes; however, their binding property and functional roles in PSI are still missing. We analyzed a cryo-electron microscopy structure of a PSI-IsiA supercomplex isolated from Anabaena grown under an iron-deficient condition. The PSI-IsiA structure contains six IsiA subunits associated with the PsaA side of a PSI core monomer. Three of the six IsiA subunits are identified as IsiA1 and IsiA2. The PSI-IsiA structure lacks a PsaL subunit; instead, a C-terminal domain of IsiA2 is inserted at the position of PsaL, which inhibits the oligomerization of PSI, leading to the formation of a monomer. Furthermore, excitation-energy transfer from IsiAs to PSI appeared with a time constant of 55 ps. These findings provide novel insights into both the molecular assembly of the Anabaena IsiA family and the functional roles of IsiAs.

plant biology↗

bioRxiv2021

The two-component response regulator OrrA confers dehydration tolerance by regulating anaKa expression in the cyanobacterium Anabaena sp. strain PCC 7120

The aquatic cyanobacterium Anabaena sp. strain PCC 7120 exhibits dehydration tolerance. The regulation of gene expression in response to dehydration is crucial for the acquisition of dehydration tolerance, but the molecular mechanisms underlying dehydration responses remain unknown. In this study, the functions of the response regulator OrrA in the regulation of salt and dehydration responses were investigated. Disruption of orrA abolished or diminished the induction of hundreds of genes in response to salt stress and dehydration. Thus, OrrA is a principal regulator of both stress responses. In particular, OrrA plays a crucial role in dehydration tolerance because an orrA disruptant completely lost the ability to regrow after dehydration. Moreover, in the OrrA regulon, anaKa encoding a protein of unknown function was revealed to be indispensable for dehydration tolerance. OrrA and AnaK are conserved among the terrestrial cyanobacteria, suggesting their conserved functions in dehydration tolerance in cyanobacteria.

microbiology↗

bioRxiv2020

The CRP-family transcriptional regulator DevH regulates expression of heterocyst-specific genes at the later stage of differentiation in the cyanobacterium Anabaena sp. strain PCC 7120

Heterocysts are terminally differentiated cells of filamentous cyanobacteria, which are specialized for nitrogen fixation. Because nitrogenase, an enzyme for nitrogen fixation, is easily inactivated by oxygen, the intracellular environment of heterocysts is kept microoxic. In heterocysts, the oxygen-evolving photosystem II is inactivated, a heterocyst-specific envelope with an outer polysaccharide layer and an inner glycolipid layer is formed to limit oxygen entry, and oxygen consumption is activated. Heterocyst differentiation, which is accompanied by drastic morphological and physiological changes, requires strictly controlled gene expression systems. Here, we investigated the functions of a CRP-family transcriptional regulator, DevH, in the process of heterocyst differentiation. A devH-knockdown strain, devHKD, was created by replacing the original promoter with the gifA promoter, which is repressed during heterocyst differentiation. Although devHKD formed morphologically distinct cells with the heterocyst envelope polysaccharide layer, it was unable to grow diazotrophically. Genes involved in construction of the microoxic environment, such as cox operons and the hgl island, were not upregulated in devHKD. Moreover, expression of the nif gene cluster was completely abolished. Even under anaerobic conditions, the nif gene cluster was not induced in devHKD. Thus, DevH is necessary for the establishment of a microoxic environment and induction of nitrogenase in heterocysts.

microbiology↗

bioRxiv2019

cyAbrB transcriptional regulators as safety devices to inhibit heterocyst differentiation in Anabaena

Cyanobacteria are monophyletic organisms that perform oxygenic photosynthesis. While they exhibit great diversity, they have a common set of genes. However, the essentiality of them for viability has hampered the elucidation of their functions. One example of the genes is cyabrB1 encoding a transcriptional regulator. In the present study, we investigated the function of cyabrB1 in heterocyst-forming cyanobacterium Anabaena sp. PCC 7120 through CRISPR interference, a method we recently utilized for the photosynthetic production of a useful chemical in the strain. Conditional knockdown of cyabrB1 in the presence of nitrate resulted in formation of heterocysts. Two genes, hetP and hepA, which are required for heterocyst formation, were up-regulated by cyabrB1 knockdown in the presence of combined nitrogen sources. The genes are known to be induced by HetR, a master regulator of heterocyst formation. hetR was not induced by cyabrB1 knockdown. hetP and hepA were repressed by direct binding of cyAbrB1 to their promoter regions in a HetR-independent manner. In addition, the over-expression of cyabrB1 abolished heterocyst formation upon nitrogen depletion. Also, knockout of cyabrB2, a paralogue gene of cyabrB1, in addition to cyabrB1 knockdown, enhanced heterocyst formation in the presence of nitrate, suggesting functional redundancy of cyAbrB proteins. We propose that a balance between amounts of HetR and cyAbrB1 is a key factor influencing heterocyst differentiation during nitrogen step-down. cyAbrB proteins are essential safety devices inhibiting heterocyst differentiation. ImportanceSpore formation in Bacillus subtilis and Streptomyces represents non-terminal differentiation and has been extensively studied as models of prokaryotic cell differentiation. In the two organisms, many cells differentiate simultaneously, and the differentiation is governed by a network in which one regulator stands at the top. Differentiation of heterocysts in Anabaena sp. PCC 7120 has also been extensively studied. The differentiation is unique because it is terminal and only 5-10% vegetative cells differentiate into heterocysts. In the present study, we identified cyAbrB1 as a repressor of two genes that are essential for heterocyst formation, hetP and hepA, independent of HetR, which is a master activator for heterocyst differentiation. The finding is reasonable for unique cell differentiation of Anabaena because cyAbrB1 could suppress heterocyst differentiation tightly in vegetative cells, while only cells in which HetR is over-expressed could differentiate into heterocysts.

microbiology↗