Biology subjects

Sakakibara, H.

Publications and source records attributed to Sakakibara, H..

At least 19 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↗

bioRxiv2026

LBD-type transcription factors suppress local and systemic nitrogen responses through distinct regulatory pathways

Nitrogen (N) is a major determinant of plant growth and productivity. Because soil N availability and internal N demand fluctuate, plants have evolved sophisticated mechanisms to coordinate N acquisition and utilization at the whole-plant level. However, how this coordination is achieved remains poorly understood. Here, we show that N-inducible LATERAL ORGAN BOUNDARIES DOMAIN transcription factors LBD37, LBD38, and LBD39 (LBDs) function as repressors of local N uptake and assimilation and systemic N-demand signaling in Arabidopsis. Triple mutants lacking these three LBDs displayed enhanced nitrate influx and increased accumulation of nitrate, amino acids, and total N. Transcriptome analysis identified an array of N-starvation- and nitrate-inducible genes derepressed in shoots and roots, including C-TERMINALLY ENCODED PEPTIDE (CEP) and CEP DOWNSTREAM (CEPD) genes, as well as genes involved in N uptake and assimilation. Grafting and genetic analyses revealed that LBDs gate the systemic N-demand signaling relay by repressing CEP and CEPD expression organ-autonomously. We also found that LBDs locally repress genes involved in N uptake and assimilation through a distinct regulatory mechanism. We propose that LBDs are key transcriptional repressors in a regulatory framework for optimizing N acquisition and utilization under fluctuating N conditions at the whole-plant level.

plant biology↗

bioRxiv2026

The submergence-induced drastic morphological plasticity of root in the amphibious plant Callitriche palustris

Amphibious plants can thrive in both terrestrial and submerged environments, which are fundamentally distinct. Although morphological plasticity of leaf known as heterophylly has been well investigated, the morphological plasticity of root in amphibious plants remains poorly understood. In this study, we discovered that an amphibious plant Callitriche palustris (Plantaginaceae), which has significant heterophylly, has a remarkable morphological plasticity also in root in response to submergence. This species develops thin roots with abundant root hairs, fewer cortical and epidermal cells, and smaller aerenchyma in the terrestrial condition. On the other hand, it develops thicker roots with few root hairs, more cortical and epidermal cells, and larger aerenchyma in the submerged condition. We call this morphological plasticity of root as "heterorhizy". Phytohormone perturbation experiments revealed that abscisic acid (ABA) and gibberellin regulate root hair development and root cell division respectively. We also found the possibility that heterorhizy was acquired in the genus Callitriche. Additionally, a similar form of root hair plasticity was also observed in the phylogenetically distinct amphibious species Ludwigia arcuata (Onagraceae). Furthermore, the absence of root hair development underwater and the similar structure of aerenchyma to C. palustris were broadly seen across diverse aquatic plants. This study provides new insights into the root morphological responses to submerged environments in aquatic plants.

plant biology↗

bioRxiv2025

Cytokinin receptor AHK3 modulates root-to-shoot transport of trans-zeatin type cytokinin

Trans-zeatin (tZ)-type cytokinins (CKs) are synthesized in roots in response to nitrate, transported to shoot via xylem, and coordinate diverse physiological processes in aerial organs. Within this mechanism, the regulation of CK biosynthesis by nitrate signaling via NIN-like protein 7 as well as the loading of tZ-type CKs into xylem by ATP-binding cassette transporter G14 have been well studied. However, the roles of other components remain unclear. Here, we show that CK perception and degradation in roots, as mediated by Arabidopsis histidine kinase 3 (AHK3) and CK oxidase/dehydrogenase 4 (CKX4), modulate xylem tZ-type CKs transport and leaf CK status. Grafting experiments demonstrated that root-specific AHK3 deficiency systemically increased leaf blade area through long-distance signals of root-derived tZ-type CK, perceived by shoot-expressed AHK3. Transcriptome and hormonome analyses revealed that root-specific AHK3 deficiency reduced CKX4 expression in roots, elevating tZ-type CK levels in roots and xylem sap and thereby enhancing leaf CK response. Transfer experiments manipulating root nitrate levels showed that root-specific AHK3 deficiency promoted leaf blade area in a manner dependent on both nitrate and root-derived tZ-type CK signaling. Moreover, both nitrate signals and root-expressed AHK3 are required for maximal CKX4 induction in roots, and root-specific CKX4 deficiency enhanced leaf blade area in a nitrate-dependent manner. These findings reveal a novel mechanism in which an AHK3-CKX4 module governs xylem transport of tZ-type CKs, fine-tuning leaf size according to nitrogen availability in roots. SIGNIFICANCE STATEMENTTo clarify a mechanism that attenuates trans-zeatin-type cytokinin transport from roots to shoots in response to nitrate signaling, this study examined the root-specific role of cytokinin receptors. Our results show that cytokinin perception and degradation, as mediated by Arabidopsis histidine kinase 3 and cytokinin oxidase/dehydrogenase 4, modulate xylem trans-zeatin-type cytokinin transport, thereby fine-tuning leaf cytokinin status and growth in a nitrate-dependent manner, providing new insights into long-distance cytokinin transport according to nitrogen availability.

plant biology↗

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

Shoot nitrate status regulates Arabidopsis shoot growth and systemic transcriptional responses via shoot adenylate isopentenyltransferase 3

Plants systemically regulate growth and gene expression according to their internal nitrate status. Our previous study reported that shoot nitrate accumulation increases shoot expression of adenosine phosphate-ISOPENTENYLTRANSFERASE 3 (IPT3) and shoot levels of N6-({Delta}2-isopentenyl) adenine (iP)-type cytokinins (CKs). IPT3 expression is localized in the phloem, and iP-type CKs, which are synthesized by IPT3, are phloem-mobile. As CKs are a class of phytohormones that control growth and genome-wide gene expression, shoot-expressed IPT3 may mediate the systemic regulation of growth and transcriptomic responses to shoot nitrate status. To examine this, we developed a novel system to manipulate nitrate levels and IPT3 expression in a shoot-specific manner and performed growth analysis, CK determination, and RNA-sequencing. Our results demonstrated that shoot nitrate accumulation significantly promoted shoot growth and elevated shoot concentrations of iP ribotides, iP-7-N-glucoside, and iP-9-N-glucoside through the action of shoot IPT3. Transcriptomic responses to shoot nitrate accumulation were largely tuned by shoot IPT3, with opposite effects in shoots and roots. Shoot IPT3 amplified shoot responses of nitrate-inducible genes and immune response genes to shoot nitrate accumulation, while it dampened root responses of nitrate transport/assimilation genes. This transcriptomic modulation via shoot IPT3 was accompanied by coherent transcriptional changes in genes encoding mobile peptides and transcriptional repressors. Here we present a novel scheme integrating shoot nitrate status responses with CK signaling.

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

Multiomics-based assessment of the impact of airflow on diverse plant callus cultures

Plant cell culture has multiple applications in biotechnology and horticulture, from plant propagation to the production of high-value biomolecules. However, the interplay between cellular diversity and ambient conditions influences the metabolism of cultured tissues; understanding these factors in detail will inform efforts to optimize culture conditions. This study presents multiomics datasets from callus cultures of tobacco (Nicotiana tabacum), rice (Oryza sativa), and two bamboo species (Phyllostachys nigra and P. bambusoides). Over four weeks, calli were cultured under continuous moisture without airflow or gradually reduced ambient moisture with airflow. For each sample, gene expression was profiled with high-throughput RNA sequencing, 442 metabolites were measured using liquid chromatography (LC) with triple-quadrupole mass spectrometry (LC-QqQMS), and 31 phytohormones were quantified using ultra-performance LC coupled with a tandem quadrupole mass spectrometer equipped with an electrospray interface (UPLC-ESI-qMS/MS) and ultra-high-performance LC- orbitrap MS (UHPLC-Orbitrap MS). These datasets highlight the impact of airflow on callus cultures, revealing differences between and within species, and provide a comprehensive resource to explore the physiology of callus growth.

plant biology↗

bioRxiv2024

Arabidopsis ABCC4 encodes a cytokinin efflux transporter and is involved in root system development

The directional and sequential flow of cytokinin in plants is organized by a complex network of transporters. Genes involved in several aspects of cytokinin transport have been characterized, but a large part of the elaborate system remains elusive. In this study, we have identified ABCC4 as a cytokinin efflux transporter gene. Using a transient expression system in tobacco leaves, we screened Arabidopsis transporter genes and isolated ATP-BINDING CASSETTE TRANSPORTER C4 (ABCC4). Further validation through drug-induced expression in Arabidopsis and heterologous expression in budding yeast revealed that ABCC4 effluxes the active form of cytokinins. During the seedling stage, ABCC4 was highly expressed in roots, and its expression was up-regulated in response to cytokinin application. Loss-of-function mutants of ABCC4 displayed enhanced primary root elongation, similar to mutants impaired in cytokinin biosynthesis or signaling, which was suppressed by exogenous trans-zeatin treatment. In contrast, overexpression of the gene led to suppression of root elongation. These results suggest that ABCC4 plays a role in the efflux of active cytokinin, thereby contributing to root growth regulation. Our findings contribute to unraveling the many complexities of cytokinin flow and enhance our understanding of the regulatory mechanisms underlying root system development in plants.

plant biology↗

bioRxiv2024

STOP1 dominates Arabidopsis tolerance to ammonium over NRT1.1/NPF6.3/CHL1

The Arabidopsis nitrate transceptor NITRATE TRANSPORTER 1.1 (NRT1.1/NPF6.3/CHL1) plays significant roles even in the absence of nitrate. The loss-of-function of NRT1.1 alleviates growth suppression and chlorosis under toxic levels of ammonium as the sole nitrogen source. Recently, we reported that acidic stress-inducible genes are downregulated by NRT1.1 deficiency under ammonium toxicity conditions, implying that NRT1.1 may exacerbate ammonium-dependent acidic stress. The transcription factor SENSITIVE TO PROTON RHIZOTOXICITY 1 (STOP1) enhances Arabidopsis tolerance to ammonium and acidic stresses. Furthermore, STOP1 directly activates NRT1.1 transcription. These previous findings prompted us to analyze the association between NRT1.1 and STOP1 on ammonium tolerance. Here, we show that ammonium-inducible STOP1 plays a dominant role over NRT1.1 in ammonium tolerance and expression of direct target genes of STOP1. We present a novel scheme in which NRT1.1 and STOP1 jointly regulate common target(s) associated with ammonium tolerance.

plant biology↗

bioRxiv2024

Brassinosteroids function as the plant male and female reproductive hormone coordinating gene expression.

Brassinosteroids (BRs) are steroid hormones identified in plants. Besides promoting cell elongation and division, BRs facilitate the development of both male and female reproductive tissues. In animals, reproductive steroid hormones play an essential role in reproductive tissue development by regulating gene expression. Here, we focused on the function of BRs during fertilization. We measured the content of biologically active BRs, brassinolide (BL) and castasterone (CS), in the reproductive tissues of Arabidopsis thaliana. Both BL and CS accumulated abundantly in pollen grains and in larger amounts in pistils than in leaves. To evaluate BL function during fertilization, we used an in vitro guidance assay with exogenously applied BL. Although pollen tubes need to be elongated through the pistils for efficient capacitation, BL treatment promoted pollen tube capacitation and improved attraction to ovules in vitro. Transcriptome analysis demonstrated that BL treatment induced the expression of half of the genes expressed in pollen tubes that elongated through the pistils. These results indicated that BL supplied from pistils is a key factor for pollen tube capacitation. However, using the bri1 mutant for the guidance assay resulted in reduced pollen tube capacitation, suggesting that BRI1-signaling in pistils is also important. Furthermore, BRs act on ovules. Exogenous BL application to ovules maintained guidance capacity by promoting the expression of small secreted proteins involved in pollen tube attraction and gamete fusion. Overall, BRs play a significant role as male and female reproductive hormones throughout the plant fertilization process.

plant biology↗

bioRxiv2024

CONCERTED PLANT GROWTH AND DEFENSE THROUGH TARGETED PHYTOHORMONE CROSSTALK MODIFICATION

Plant immunity activation often results in suppression of plant growth, particularly in the case of constitutive immune activation. We discovered that signaling of the phytohormone cytokinin (CK), known to regulate plant growth through the control of cell division and shoot apical meristem (SAM) activity, can be suppressed by negative crosstalk with the defense phytohormones jasmonic acid (JA), and most evidently, salicylic acid (SA). We show that changing the negative crosstalk of SA on CK signaling in autoimmunity mutants by targeted increase of endogenous CK levels results in plants resistant to pathogens from diverse lifestyles, and relieves suppression of reproductive growth. Moreover, such changes in crosstalk result in a novel reproductive growth phenotype, suggesting a role for defense phytohormones in the SAM, likely through regulation of nitrogen response and cellular redox status. Our data suggest that targeted phytohormone crosstalk engineering can be used to achieve increased reproductive growth and pathogen resistance. SIGNIFICANCE STATEMENTPlants constantly integrate environmental stimuli with developmental programs to optimize their growth and fitness. Excessive activation of the plant immune system often leads to decreased plant growth, a process known as the growth-defense tradeoff. Here, we adapted phytohormone levels in Arabidopsis reproductive tissues of autoimmunity mutants to change phytohormonal crosstalk and diminish the growth tradeoff, resulting in increased broad resistance to pathogens and decreased growth suppression. Similar approaches to phytohormone crosstalk engineering could be used in different contexts to achieve outcomes of higher plant stress resilience and yield.

plant biology↗

bioRxiv2024

Large-scale single-cell profiling of stem cells uncovers redundant regulators of shoot development and yield trait variation

Stem cells in plant shoots are a rare population of cells that produce leaves, fruits and seeds, vital sources for food and bioethanol. Uncovering regulators expressed in these stem cells will inform crop engineering to boost productivity. Single-cell analysis is a powerful tool for identifying regulators expressed in specific groups of cells. However, accessing plant shoot stem cells is challenging. Recent single-cell analyses of plant shoots have not captured these cells, and failed to detect stem cell regulators like CLAVATA3 and WUSCHEL. In this study, we finely dissected stem cell-enriched shoot tissues from both maize and arabidopsis for single-cell RNA-seq profiling. We optimized protocols to efficiently recover thousands of CLAVATA3 and WUSCHEL expressed cells. A cross-species comparison identified conserved stem cell regulators between maize and arabidopsis. We also performed single-cell RNA-seq on maize stem cell overproliferation mutants to find additional candidate regulators. Expression of candidate stem cell genes was validated using spatial transcriptomics, and we functionally confirmed roles in shoot development. These candidates include a family of ribosome-associated RNA-binding proteins, and two families of sugar kinase genes related to hypoxia signaling and cytokinin hormone homeostasis. These large-scale single-cell profiling of stem cells provide a resource for mining stem cell regulators, which show significant association with yield traits. Overall, our discoveries advance the understanding of shoot development and open avenues for manipulating diverse crops to enhance food and energy security.

plant biology↗

bioRxiv2024

The endophytic fungus Serendipita indica alters auxin distribution in Arabidopsis thaliana roots through alteration of auxin transport and conjugation to promote plant growth

Plants share their habitats with a multitude of different microbes. This close vicinity promoted the evolution of inter-organismic interactions between plants and many different microorganisms that provide mutual growth benefits both to the plant and the microbial partner. The symbiosis of Arabidopsis thaliana with the beneficial root colonizing endophyte Serendipita indica represents a well-studied system. Co-colonization of Arabidopsis roots with S. indica significantly promotes plant growth. Due to the notable phenotypic alterations of fungus-infected root systems, the involvement of a reprogramming of plant hormone levels, especially that of indole-3-acetic acid, has been suggested earlier. However, until now, the molecular mechanism by which S. indica promotes plant growth remains largely unknown. This study used comprehensive transcriptomics, metabolomics, reverse genetics, and life cell imaging to reveal the intricacies of auxin-related processes that affect root growth in the symbiosis between A. thaliana and S. indica. Our experiments revealed the essential role of tightly controlled auxin conjugation in the plant-fungus interaction. It particularly highlighted the importance of two GRETCHEN HAGEN 3 (GH3) genes, GH3.5 and GH3.17, for the fungus infection-triggered stimulation of biomass production, thus broadening our knowledge about the function of GH3s in plants. Furthermore, we provide evidence for the transcriptional alteration of the PIN2 auxin transporter gene in roots of Arabidopsis seedlings infected with S. indica and demonstrate that this transcriptional adjustment affects auxin signaling in roots, which results in increased plant growth.

plant biology↗

bioRxiv2023

Genetic and transcriptomic dissection of nitrate-independent function of Arabidopsis NRT1.1/NPF6.3/CHL1 under high ammonium condition

The Arabidopsis nitrate transceptor NRT1.1/NPF6.3/CHL1 regulates physiological responses to nitrate. Several studies have reported that Arabidopsis plants lacking NRT1.1 show enhanced shoot growth under toxic levels of ammonium without nitrate, suggesting a nitrate-independent function for NRT1.1. To further investigate this nitrate-independent function and its impact on ammonium tolerance, we conducted genetic analysis, tissue-specific expression analysis, and transcriptome analysis using various NRT1.1-related lines. Transgenic plants expressing either nonphosphomimic or phosphomimic mutants of NRT1.1 exhibited similar ammonium tolerance to the wild-type. The chl1-9 mutant, in which NRT1.1 with the P492L substitution is localized intracellularly rather than at the plasma membrane and fails to transport nitrate, showed significantly improved ammonium tolerance. Confocal imaging revealed that the NRT1.1-GFP signal was detected in the plasma membrane of various tissues, including cotyledon pavement cells, hypocotyl epidermal cells, mesophyll cells, root cap cells, and epidermal cells near root tips. In early seedlings, the absence of functional NRT1.1 altered the expression of genes associated with aliphatic glucosinolate biosynthesis, ethylene signaling, and low pH stress. Genes predicted to encode products localized to the extracellular space were enriched among those differentially expressed due to NRT1.1 deficiency. Our data suggest that in the absence of nitrate, plasma membrane-targeted NRT1.1 reduces ammonium tolerance irrespective of its phosphorylation state with alterations of gene expression associated with stress and senescence.

plant biology↗

bioRxiv2022

The trans-zeatin-type side-chain modification of cytokinins controls rice growth

Cytokinins (CKs), a class of phytohormones with vital roles in growth and development, occur naturally with various side-chain structures, including N6-({Delta}2-isopentenyl)adenine-, cis-zeatin- and trans-zeatin (tZ)-types. Recent studies in a model dicot plant Arabidopsis demonstrated that tZ-type CKs are biosynthesized via cytochrome P450 monooxygenase (P450) CYP735A, and have a specific function in shoot growth promotion. Although the function of some of these CKs has been demonstrated in a few dicotyledonous plant species, the significance of these variations and their biosynthetic mechanism and function in monocots and in plants with distinctive side-chain profiles than Arabidopsis, such as Oryza sativa (rice), remain elusive. In this study, we characterized CYP735A3 and CYP735A4 to investigate the role of tZ-type CKs in rice. Complementation test of the Arabidopsis CYP735A-deficient mutant and CK profiling of loss-of-function rice mutant, cyp735a3 cyp735a4, demonstrated that CYP735A3 and CYP735A4 encode P450s required for tZ-type side-chain modification in rice. CYP735As are expressed in both roots and shoots. The cyp735a3 cyp735a4 mutants exhibited growth retardation concomitant with reduction in CK activity in both roots and shoots, indicating that tZ-type CKs function in growth promotion of both organs. Expression analysis revealed that tZ-type CK biosynthesis is negatively regulated by auxin, abscisic acid, and cytokinin and positively by dual nitrogen nutrient signals, namely glutamine-related and nitrate-specific signals. These results suggest that the physiological role of tZ-type CKs in rice is different from that in Arabidopsis and they control growth of both roots and shoots in response to internal and environmental cues in rice.

plant biology↗

bioRxiv2022

Photosynthetic-product-dependent Activation of Plasma Membrane H+-ATPase and Nitrate Uptake in Arabidopsis Leaves.

Plasma membrane (PM) H+-ATPase is a pivotal enzyme for plant growth and development that acts as a primary transporter and is activated by phosphorylation of the penultimate residue, threonine, at the C-terminus. Photosynthetically active radiation activates PM H+-ATPase via phosphorylation in mesophyll cells of Arabidopsis thaliana, and phosphorylation of PM H+-ATPase depends on photosynthesis and photosynthesis-related sugar supplementation, such as sucrose, fructose and glucose. However, the molecular mechanism and the physiological role of photosynthesis-dependent PM H+-ATPase activation are still unknown. Analysis using sugar analogues, such as palatinose, turanose, and 2-deoxy glucose, revealed that sucrose metabolites and products of glycolysis such as pyruvate induce phosphorylation of PM H+-ATPase. Transcriptome analysis showed that novel isoform of the Small Auxin Up RNA genes, SAUR30, is upregulated in a light- and sucrose-dependent manner. Time course analyzes of sucrose supplementation showed that phosphorylation level of PM H+-ATPase increased within 10 min, but expression level of SAUR30 increased later than 10 min. The results suggest two temporal regulations may participate in the regulation of PM H+-ATPase. Interestingly, a 15NO3- uptake assay in leaves showed that light increases 15NO3- uptake, and that increment of 15NO3- uptake depends on PM H+-ATPase activity. The results opened the possibility of physiological role of photosynthesis-dependent PM H+-ATPase activation in the uptake of NO3-. We speculate that PM H+-ATPase may connect photosynthesis and nitrogen metabolism in leaves.

plant biology↗

bioRxiv2021

Root-specific reduction of cytokinin perception enhances shoot growth with an alteration of trans-zeatin distribution in Arabidopsis thaliana

Compelling evidence demonstrates that root-derived cytokinins (CKs) contribute to shoot growth via long-distance transport; therefore, we hypothesized that an increase in root-derived CKs enhances shoot growth. To demonstrate this, we grafted Arabidopsis Col-0 (WT) scion onto rootstock originated from WT or a double-knockout line of CK receptors AHK2 and AHK3 (ahk23) because the knockout line over accumulates CKs in the body due to feedback homeostasis regulation. The grafted plants (scion/rootstock: WT/WT and WT/ahk23) were grown in vermiculite pots or solid media under high and low nitrogen regimes for vegetative growth and biochemical analysis. The root-specific deficiency of AHK2 and AHK3 increased root concentrations of trans-zeatin (tZ)-type and N6-({Delta}2-isopentenyl) adenine (iP)-type CKs, induced CK biosynthesis genes, and repressed CK degradation genes in the root. Shoot growth, shoot concentrations of tZ-type CKs, and shoot expression of CK-inducible marker genes were consistently larger in the WT/ahk23 plants than in the WT/WT plants. Moreover, the root-specific deficiency of AHK2 and AHK3 enhanced shoot growth in the WT scion more strongly than in the ahk23 scion. Given that tZ-type CKs are predominantly produced from iP-type CKs in the root and xylem-mobile, it is concluded that the root-specific reduction of CK perception would enhance shoot growth by increasing the amount of root-derived tZ-type CKs and their perception by the shoot. This study will present a novel approach to improve plant growth and productivity.

plant biology↗