Biology subjects

Komatsu, A.

Publications and source records attributed to Komatsu, A..

8 recordsLinked to original sources

bioRxiv2025

MAX2-dependent signaling regulates the transition from 2D to 3D growth by suppressing cytokinin accumulation in Physcomitrium patens

Plants undergo distinct developmental phases throughout their life cycle. Proper regulation of the timing of phase transition in response to internal and external cues is crucial to optimize proliferation and reproduction. In Physcomitrium patens (P. patens), a moss, the transition from growth of filamentous tissue growth called protonema to gametophore bud formation represents a shift from two-dimensional (2D) to three-demensional (3D) growrh, ultimately leading to reproductive development. MORE AXILLARY GROWTH2 (MAX2), an F-box protein, targets repressor proteins in the KARRIKIN INSENSITIVE2 (KAI2)-dependent signaling pathway for degradation via the 26S proteasome-dependent pathway. KAI2 perceives an unidentified ligand known as KAI2 ligand (KL) as well as karrikins. The four SMAX1-LIKE (SMXL) family proteins work as suppressors in the MAX2-dependent signaling in P. patens. Gametophore bud formation was accelerated when MAX2-dependent signaling was disrupted, while it was delayed in Ppsmxls, loss of function mutants of the PpSMXLs. These results indicate that MAX2-dependent signaling suppresses gametophore bud formation in P. patens, which has not been previously described. We demonstrate that cytokinin activity and contents are increased in Ppmax2 mutants, and cytokinin application rescued the delay in bud formation in Ppsmxl mutants, suggesting that MAX2-dependent signaling suppresses cytokinin accumulation. The four SMXL genes redundantly act to promote gametophore bud formation; PpSMXLC and PpSMXLD, which contain the conserved degron sequence, act as the repressor of MAX2-dependent signaling, while PpSMXLA and PpSMXLB function independent of proteolysis-dependent signaling. Based on these findings, we propose that modulating cytokinin activity to control developmental phase transition may be a conserved role of MAX2-dependent signaling in bryophytes. Significance StatementPlant hormones, both individually and in combination, regulate almost all aspects of plant growth and development. Gametophore bud formation in Physcomitrium patens, a moss, marks the transition from two-dimensional (2D) filamentous growth to three-dimensional (3D) shoot growth. We demonstrate that gametophore bud formation is controlled by the sequential action of two plant hormones, KL, an unidentified hormone that is transduced through MAX2-dependent signaling, and cytokinin. Four SMXL genes, repressors in MAX2-dependent signaling, redundantly promote bud formation: two function within the signaling pathway, while the other two operate independently of it. Our findings uncover novel mechanisms that directly link MAX2-dependent signaling to developmental phase transition by regulating stem cell activity, achieved through the regulation of cytokinin accumulation in Physcomitrium patens.

plant biology↗

bioRxiv2024

Evolutionary acquisition of a primitive light-dependent nuclear relocation in Marchantia polymorpha

The terrestrialization of plants was accompanied by exposure to several environmental stresses. Adaptation to these stresses required numerous changes at the cellular and molecular level. One such adaptation in the leaves of Arabidopsis thaliana is the movement of cell nuclei to avoid UV damage. In the dark, the nuclei locate to the bottom walls of leaf cells to distance genetic material from external stresses, but in response to intense blue light (an indication of the presence of UV), they move to the side walls to escape UV-induced DNA damage1. The movement is driven by the photoreceptor phototropin and the actin cytoskeleton2. However, how this protective mechanism evolved in land plants remains unclear. Here, we show that in the liverwort Marchantia polymorpha, nuclei show a similar, but less stable movement in response to intense blue light. In the dark, M. polymorpha positioned nuclei on the upper walls of epidermal cells in young thalli, but in response to intense blue light, the nuclei immediately moved to the side walls, similar to A. thaliana. However, the movement was transient and the nuclei returned to the upper walls through both the actin and microtubule cytoskeletons. Unlike A. thaliana, M. polymorpha responded to prolonged (> 1 day) exposure to low light by moving nuclei from the upper to the side walls through both the actin and microtubule cytoskeletons and two photoreceptors (phototropin and phytochrome). However, no light-dependent nuclear relocation was observed in charophyte algae, suggesting that light-dependent nuclear relocation was initially established in the common ancestor of land plants as a result of terrestrialization and then diverged during land plant evolution.

plant biology↗

bioRxiv2024

KAI2-dependent signaling controls vegetative reproduction in Marchantia polymorpha through activation of LOG-mediated cytokinin synthesis

Marchantia polymorpha reproduces vegetatively (asexually) by producing propagules known as gemmae within gemma cups and sexually through spores. We previously reported that KARRIKIN INSENSITIVE 2 (KAI2)-dependent signaling promotes gemma cup and gemma formation. KAI2A perceives unidentified endogenous ligand(s), tentatively referred to as KAI2 ligands (KL). Perception of KL by KAI2 triggers MAX2-dependent proteolysis of MpSMXL. In this study, we identified genes working downstream of KAI2-dependent signaling in M. polymorpha. We found that KAI2-dependent signaling positively controls the expression of MpLONLEY GUY (MpLOG), encoding a cytokinin biosynthesis enzyme. Disruption of the MpLOG function decreased endogenous cytokinin levels and caused defects similar to KAI2-dependent signaling mutants. Moreover, supplying exogenous cytokinins rescued the defects of Mplog and KAI2-dependent signaling mutants, implying that cytokinins work downstream of KAI2-dependent signaling. Activation of MpLOG by KAI2-dependent signaling occurs in a highly cell-type-specific manner, leading to cell-specific induction of GEMMA CUP-ASSOCIATED MYB1 (GCAM1), the master regulator of vegetative reproduction of M. polymorpha. We propose a genetic cascade, starting from KAI2-dependent signaling, that promotes vegetative reproduction through the induction of MpLOG and GCAM1. The interaction between KAI2-dependent signaling and cytokinin in M. polymorpha provides a novel insight into the function and evolution of KAI2-dependent signaling.

plant biology↗

bioRxiv2024

Exploring 3-Aminobenzoic Acid as a Therapeutic Dietary Component for Enhancing Intestinal Barrier Integrity in Ulcerative Colitis

BackgroundDietary components and their metabolites produced by intestinal bacteria play a crucial role in maintaining intestinal epithelial integrity. Disrupted epithelial integrity increases permeability and leads to chronic inflammation in the colon, known as ulcerative colitis (UC), in genetically predisposed individuals. However, the gut microbial metabolites regulating epithelial permeability remain unexplored and their metabolism in UC patients is unclear. MethodsA library of 119 gut microbial metabolites was screened for their ability to reduce epithelial permeability in Caco2 cell monolayers. The diet containing 3-aminobenzoic acid (3-ABA) was identified using liquid chromatography with quadrupole time-of-flight mass spectrometry. The abundance of fecal 3-ABA was compared between UC patients and healthy individuals followed by 16S rRNA metagenomic analysis to estimate the gut microbial function in ABA degradation. The anti-inflammatory effect of 3-ABA was examined in a mouse model of dextran sodium sulfate-induced colitis. ResultsStimulation with 3-ABA reduced epithelial permeability and enhanced barrier integrity in Caco2 cells by modulating the tight junctional regulatory pathway. 3-ABA was abundant in beans and decreased in the feces of UC patients. Functional prediction analysis of gut microbiota revealed an accelerated degradation of ABA with significant up-regulation of mabA, a gene encoding a bacterial enzyme involved in 3-ABA degradation, in UC patients. Rectal and oral administration of 3-ABA ameliorated experimental colitis in mice. Conclusion3-ABA abundant in beans enhanced intestinal epithelial integrity and ameliorated experimental colitis in mice. Proactive intake of 3-ABA might be a novel treatment approach for UC.

molecular biology↗

bioRxiv2023

Harnessing deep learning to analyze cryptic morphological variability of Marchantia polymorpha

Characterizing phenotypes is a fundamental aspect of biological sciences, although it can be challenging due to various factors. For instance, the liverwort (Marchantia polymorpha), a model system for plant biology, exhibits morphological variability, making it difficult to identify and quantify distinct phenotypic features using objective measures. To address this issue, we utilized a deep learning-based image classifier that can handle plant images directly without manual extraction of phenotypic features, and analyzed bright-field images of M. polymorpha. This dioicous plant species exhibits morphological differences between male and female wild accessions at an early stage of gemmaling growth, although it remains elusive whether the differences are attributable to sexual dimorphism or autosomal genetic variation. To dissect the genomic factors, we established a male and female set of recombinant inbred lines (RILs) from a set of male and female wild accessions. We then trained deep-learning models to classify the sexes of the RILs and the wild accessions. Our results showed that the trained classifiers accurately classified male and female gemmalings of wild accessions in the first week of growth, confirming the intuition of plant researchers in a reproducible and objective manner. In contrast, the RILs were less distinguishable, indicating that the differences between the parental wild accessions arose from autosomal variations instead of sexual dimorphism. Furthermore, we validated our trained models by an "explainable AI" technique that highlights image regions relevant to the classification. Our findings demonstrate that the classifier-based approach provides a powerful tool for analyzing plant species that lack standardized phenotyping metrics.

plant biology↗

bioRxiv2022

KARRIKIN INSENSITIVE2 (KAI2)-dependent signaling pathway controls vegetative reproduction in Marchantia polymorpha

In vegetative reproduction of Marchantia polymorpha, propagules, called gemmae, are formed in gemma cups. Despite its significance for survival, control of gemma and gemma cup formation by environmental cues is not well understood. We show here that the number of gemmae formed in a gemma cup is a genetic trait. Gemma formation starts from the central region of the floor of the gemma cup, proceeds to the periphery, and terminates when the appropriate number of gemmae are initiated. The MpKARRIKIN INSENSITIVE2 (MpKAI2)-dependent signaling pathway promotes gemma cup formation and gemma initiation. The number of gemmae in a cup is controlled by modulating the ON/OFF switch of the KAI2-dependent signaling. Termination of the signaling results in the accumulation of MpSMXL, a suppressor protein. In the Mpsmxl mutants, gemma initiation continues, leading to the formation of a highly increased number of gemmae in a cup. Consistent with its function, the MpKAI2-dependent signaling pathway is active in gemma cups where gemmae initiate, as well as in the notch region of the mature gemma and midrib of the ventral side of the thallus. In this work, we also show that GEMMA CUP-ASSOCIATED MYB1 works downstream of this signaling pathway to promote gemma cup formation and gemma initiation. We also found that the availability of potassium affects gemma cup formation independently from the KAI2-dependent signaling pathway in M. polymorpha. We propose that the ancestral function of the KAI2-dependent signaling pathway may be to optimize vegetative reproduction by adapting to the environment.

plant biology↗

bioRxiv2021

An ancestral function of strigolactones as symbiotic rhizosphere signals

In flowering plants, carotenoid-derived strigolactones (SLs) have dual functions as hormones that regulate growth and development, and as rhizosphere signaling molecules that induce symbiosis with arbuscular mycorrhizal (AM) fungi. Here, we report the identification of bryosymbiol (BSB), a previously unidentified SL from the bryophyte Marchantia paleacea. BSB is also found in vascular plants, indicating that it is ancestral in land plants. BSB synthesis is enhanced at AM symbiosis permissive conditions and BSB deficient mutants are impaired in AM symbiosis. In contrast, the absence of BSB synthesis has little effect on the growth and gene expression. We show that the introduction of the SL receptor of Arabidopsis renders M. paleacea cells BSB-responsive. These results suggest that BSB is not perceived by M. paleacea cells due to the lack of cognate SL receptors. We propose that SLs originated as AM symbiosis-inducing rhizosphere signaling molecules and were later recruited as plant hormone.

plant biology↗

bioRxiv2020

Major components in the KARRIKIN INSENSITIVE2-ligand signaling pathway are conserved in the liverwort, Marchantia polymorpha

KARRIKIN INSENSITIVE2 (KAI2) was first identified in Arabidopsis thaliana as a receptor of karrikin, a smoke-derived germination stimulant. KAI2 is also considered a receptor of an unidentified endogenous molecule called the KAI2-ligand (KL). Upon KAI2 activation, signals are transmitted through degradation of D53/SMXL proteins via ubiquitination by a Skp-Cullin-F-box (SCF) E3 ubiquitin ligase complex. All components in the KL signaling pathway exist in the liverwort Marchantia polymorpha, namely MpKAI2A and MpKAI2B, MpMAX2 encoding the F-box protein, and MpSMXL, indicating that the signaling pathway became functional in the common ancestor of bryophytes and seed plants. Genetic analysis using knock-out mutants of these KL signaling genes, produced using the CRISPR system, indicated that MpKAI2A, MpMAX2 and MpSMXL act in the same genetic pathway and control early gemma growth. Introduction of MpSMXLd53, in which a domain required for degradation is mutated, into wild-type plants caused phenotypes resembling those of the Mpkai2a and Mpmax2 mutants. In addition, Citrine fluorescence was detected in tobacco cells transiently transformed with the 35S:MpSMXL-Citrine gene construct and treated with MG132, a proteasome inhibitor. On the other hand, introduction of 35S:MpSMXLd53-Citrine conferred Citrine fluorescence without MG132 treatment. These findings imply that MpSMXL is subjected to degradation, and that degradation of MpSMXL is crucial for KL signaling in M. polymorpha. We also showed that MpSMXL is negatively regulated by KL signaling. Taken together, this study demonstrates that basic mechanisms in the KL signaling pathway are conserved in M. polymorpha.

plant biology↗