Published Papers - Seo Mitsunori

The Dual Function of OsSWEET3a as a Gibberellin and Glucose Transporter Is Important for Young Shoot Development in Rice.

Minami Morii, Akihiko Sugihara, Sayaka Takehara, Yuri Kanno, Kyosuke Kawai, Tokunori Hobo, Masako Hattori, Hisako Yoshimura, Mitsunori Seo, Miyako Ueguchi-Tanaka

Plant & cell physiology   61 ( 11 ) 1935 - 1945   2020.12 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Translocation and long-distance transport of phytohormones are considered important processes for phytohormone responses, as well as their synthesis and signaling. Here, we report on the dual function of OsSWEET3a, a bidirectional sugar transporter from clade I of the rice SWEET family of proteins, as both a gibberellin (GA) and a glucose transporter. OsSWEET3a efficiently transports GAs in the C13-hydroxylation pathway of GA biosynthesis. Both knockout and overexpression lines of OsSWEET3a showed defects in germination and early shoot development, which were partially restored by GA, especially GA20. Quantitative reverse transcription PCR, GUS staining and in situ hybridization revealed that OsSWEET3a was expressed in vascular bundles in basal parts of the seedlings. OsSWEET3a expression was co-localized with OsGA20ox1 expression in the vascular bundles but not with OsGA3ox2, whose expression was restricted to leaf primordia and young leaves. These results suggest that OsSWEET3a is expressed in the vascular tissue of basal parts of seedlings and is involved in the transport of both GA20 and glucose to young leaves, where GA20 is possibly converted to the bioactive GA1 form by OsGA3ox2, during early plant development. We also indicated that such GA transport activities of SWEET proteins have sporadically appeared in the evolution of plants: GA transporters in Arabidopsis have evolved from sucrose transporters, while those in rice and sorghum have evolved from glucose transporters.

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The Arabidopsis NRT1/PTR FAMILY protein NPF7.3/NRT1.5 is an indole-3-butyric acid transporter involved in root gravitropism.

Shunsuke Watanabe, Naoki Takahashi, Yuri Kanno, Hiromi Suzuki, Yuki Aoi, Noriko Takeda-Kamiya, Kiminori Toyooka, Hiroyuki Kasahara, Ken-Ichiro Hayashi, Masaaki Umeda, Mitsunori Seo

Proceedings of the National Academy of Sciences of the United States of America   117 ( 49 ) 31500 - 31509   2020.12 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Active membrane transport of plant hormones and their related compounds is an essential process that determines the distribution of the compounds within plant tissues and, hence, regulates various physiological events. Here, we report that the Arabidopsis NITRATE TRANSPORTER 1/PEPTIDE TRANSPORTER FAMILY 7.3 (NPF7.3) protein functions as a transporter of indole-3-butyric acid (IBA), a precursor of the major endogenous auxin indole-3-acetic acid (IAA). When expressed in yeast, NPF7.3 mediated cellular IBA uptake. Loss-of-function npf7.3 mutants showed defective root gravitropism with reduced IBA levels and auxin responses. Nevertheless, the phenotype was restored by exogenous application of IAA but not by IBA treatment. NPF7.3 was expressed in pericycle cells and the root tip region including root cap cells of primary roots where the IBA-to-IAA conversion occurs. Our findings indicate that NPF7.3-mediated IBA uptake into specific cells is required for the generation of appropriate auxin gradients within root tissues.

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Comparative functional analyses of DWARF14 and KARRIKIN INSENSITIVE 2 in drought adaptation of Arabidopsis thaliana

Weiqiang Li, Kien Huu Nguyen, Ha Duc Chu, Yasuko Watanabe, Yuriko Osakabe, Mayuko Sato, Kiminori Toyooka, Mitsunori Seo, Lei Tian, Chunjie Tian, Shinjiro Yamaguchi, Maho Tanaka, Motoaki Seki, Lam Son Phan Tran

Plant Journal   103 ( 1 ) 111 - 127   2020.07 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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© 2020 Society for Experimental Biology and John Wiley & Sons Ltd Functional analyses of various strigolactone-deficient mutants have demonstrated that strigolactones enhance drought resistance; however, the mechanistic involvement of the strigolactone receptor DWARF14 (D14) in this trait remains elusive. In this study, loss-of-function analysis of the D14 gene in Arabidopsis thaliana revealed that d14 mutant plants were more drought-susceptible than wild-type plants, which was associated with their larger stomatal aperture, slower abscisic acid (ABA)-mediated stomatal closure, lower anthocyanin content and delayed senescence under drought stress. Transcriptome analysis revealed a consistent alteration in the expression levels of many genes related to the observed physiological and biochemical changes in d14 plants when compared with the wild type under normal and dehydration conditions. A comparative drought resistance assay confirmed that D14 plays a less critical role in Arabidopsis drought resistance than its paralog karrikin receptor KARRIKIN INSENSITIVE 2 (KAI2). In-depth comparative analyses of the single mutants d14 and kai2 and the double mutant d14 kai2, in relation to various drought resistance-associated mechanisms, revealed that D14 and KAI2 exhibited a similar effect on stomatal closure. On the other hand, D14 had a lesser role in the maintenance of cell membrane integrity, leaf cuticle structure and ABA-induced leaf senescence, but a greater role in drought-induced anthocyanin biosynthesis, than KAI2. Interestingly, a possible additive relationship between D14 and KAI2 could be observed in regulating cell membrane integrity and leaf cuticle development. In addition, our findings also suggest the existence of a complex interaction between the D14 and ABA signaling pathways in the adaptation of Arabidopsis to drought.

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The tomato DELLA protein PROCERA promotes ABA responses in guard cells by upregulating an ABA transporter.

Hagai Shohat, Natanella Illouz-Eliaz, Yuri Kanno, Mitsunori Seo, David Weiss

Plant physiology     2020.06 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Plants reduce transpiration through stomatal closure to avoid drought stress. While abscisic acid (ABA) has a central role in the regulation of stomatal closure under water-deficit conditions, we demonstrated in tomato (Solanum lycopersicum) that a gibberellin (GA) response inhibitor, the DELLA protein PROCERA (PRO), promotes ABA-induced stomatal closure and gene transcription in guard cells. To study how PRO affects stomatal closure, we performed RNAseq analysis of isolated guard cells and identified the ABA transporters ABA-IMPORTING TRANSPORTER1.1 (AIT1.1) and AIT1.2, also called NPF4.6 in Arabidopsis (Arabidopsis thaliana), as being upregulated by PRO. Tomato has four AIT1 genes, but only AIT1.1 and AIT1.2 were upregulated by PRO, and only AIT1.1 exhibited high expression in guard cells. Functional analysis of AIT1.1 in yeast confirmed its activity as an ABA transporter, possibly an importer. A CRISPR-Cas9-derived ait1.1 mutant exhibited increased transpiration, larger stomatal aperture and reduced stomatal response to ABA. Moreover, ait1.1 suppressed the promoting effects of PRO on ABA-induced stomatal closure and gene expression in guard cells, suggesting that the effects of PRO on stomatal aperture and transpiration are AIT1.1-dependent. Previous studies suggest a negative crosstalk between GA and ABA mediated by changes in hormone biosynthesis and signaling. The results of this study suggest this crosstalk is also mediated by changes in hormone transport.

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Suppression of class I compensated cell enlargement by xs2 mutation is mediated by salicylic acid signaling

Ushio Fujikura, Kazune Ezaki, Gorou Horiguchi, Mitsunori Seo, Yuri Kanno, Yuji Kamiya, Michael Lenhard, Hirokazu Tsukaya

PLoS genetics     2020.06 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

Gibberellin Promotes Fungal Entry and Colonization during Paris-Type Arbuscular Mycorrhizal Symbiosis in Eustoma grandiflorum

Takaya Tominaga, Chihiro Miura, Naoya Takeda, Yuri Kanno, Yoshihiro Takemura, Mitsunori Seo, Masahide Yamato, Hironori Kaminaka

Plant and Cell Physiology   61 ( 3 ) 565 - 575   2020.03 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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© The Author(s) 2019. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. Arbuscular mycorrhizas (AMs) are divided into two types according to morphology: Arum- and Paris-type AMs. Gibberellins (GAs) mainly inhibit the establishment of Arum-type AM symbiosis in most model plants, whereas the effects of GAs on Paris-type AM symbiosis are unclear. To provide insight into the mechanism underlying this type of symbiosis, the roles of GAs were investigated in Eustoma grandiflorum when used as the host plant for Paris-type AM establishment. Eustoma grandiflorum seedlings were inoculated with the model AM fungus, Rhizophagus irregularis, and the effects of GA and the GA biosynthesis inhibitor uniconazole-P on the symbiosis were quantitatively evaluated. Exogenous GA significantly increased hyphopodium formation at the epidermis, thus leading to the promotion of fungal colonization and arbuscule formation in the root cortex. By contrast, the suppression of GA biosynthesis and signaling attenuated fungal entry to E. grandiflorum roots. Moreover, the exudates from GA-treated roots strongly induced the hyphal branching of R. irregularis. Our results show that GA has an contrasting effect on Paris-type AM symbiosis in E. grandiflorum compared with Arum-type AM symbiosis. This finding could be explained by the differential regulation of the early colonization stage, where fungal hyphae make contact with and penetrate the epidermis.

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Autophagy increases zinc bioavailability to avoid light-mediated reactive oxygen species production under zinc deficiency

Daiki Shinozaki, Ekaterina A. Merkulova, Loreto Naya, Tetsuro Horie, Yuri Kanno, Mitsunori Seo, Yoshinori Ohsumi, Céline Masclaux-Daubresse, Kohki Yoshimoto

Plant Physiology   182 ( 3 ) 1284 - 1296   2020.03 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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© 2020 American Society of Plant Biologists. All Rights Reserved Zinc (Zn) is an essential micronutrient for plant growth. Accordingly, Zn deficiency (2Zn) in agricultural fields is a serious problem, especially in developing regions. Autophagy, a major intracellular degradation system in eukaryotes, plays important roles in nutrient recycling under nitrogen and carbon starvation. However, the relationship between autophagy and deficiencies of other essential elements remains poorly understood, especially in plants. In this study, we focused on Zn due to the property that within cells most Zn is tightly bound to proteins, which can be targets of autophagy. We found that autophagy plays a critical role during 2Zn in Arabidopsis (Arabidopsis thaliana). Autophagy-defective plants (atg mutants) failed to grow and developed accelerated chlorosis under 2Zn. As expected, 2Zn induced autophagy in wild-type plants, whereas in atg mutants, various organelle proteins accumulated to high levels. Additionally, the amount of free Zn21 was lower in atg mutants than in control plants. Interestingly, 2Zn symptoms in atg mutants recovered under low-light, iron-limited conditions. The levels of hydroxyl radicals in chloroplasts were elevated, and the levels of superoxide were reduced in 2Zn atg mutants. These results imply that the photosynthesis-mediated Fenton-like reaction, which is responsible for the chlorotic symptom of 2Zn, is accelerated in atg mutants. Together, our data indicate that autophagic degradation plays important functions in maintaining Zn pools to increase Zn bioavailability and maintain reactive oxygen species homeostasis under 2Zn in plants.

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The sugar transporter SWEET10 acts downstream of FLOWERING LOCUS T during floral transition of Arabidopsis thaliana

Fernando Andrés, Atsuko Kinoshita, Naveen Kalluri, Virginia Fernández, Vítor S. Falavigna, Tiago M.D. Cruz, Seonghoe Jang, Yasutaka Chiba, Mitsunori Seo, Tabea Mettler-Altmann, Bruno Huettel, George Coupland

BMC Plant Biology   20 ( 1 )   2020.02 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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© 2020 The Author(s). Background: Floral transition initiates reproductive development of plants and occurs in response to environmental and endogenous signals. In Arabidopsis thaliana, this process is accelerated by several environmental cues, including exposure to long days. The photoperiod-dependent promotion of flowering involves the transcriptional induction of FLOWERING LOCUS T (FT) in the phloem of the leaf. FT encodes a mobile protein that is transported from the leaves to the shoot apical meristem, where it forms part of a regulatory complex that induces flowering. Whether FT also has biological functions in leaves of wild-type plants remains unclear. Results: In order to address this issue, we first studied the leaf transcriptomic changes associated with FT overexpression in the companion cells of the phloem. We found that FT induces the transcription of SWEET10, which encodes a bidirectional sucrose transporter, specifically in the leaf veins. Moreover, SWEET10 is transcriptionally activated by long photoperiods, and this activation depends on FT and one of its earliest target genes SUPPRESSOR OF CONSTANS OVEREXPRESSION 1 (SOC1). The ectopic expression of SWEET10 causes early flowering and leads to higher levels of transcription of flowering-time related genes in the shoot apex. Conclusions: Collectively, our results suggest that the FT-signaling pathway activates the transcription of a sucrose uptake/efflux carrier during floral transition, indicating that it alters the metabolism of flowering plants as well as reprogramming the transcription of floral regulators in the shoot meristem.

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Glutathione and Its Biosynthetic Intermediates Alleviate Cesium Stress in Arabidopsis

Eri Adams, Takae Miyazaki, Shunsuke Watanabe, Naoko Ohkama-Ohtsu, Mitsunori Seo, Ryoung Shin

Frontiers in Plant Science   10   2020.01 [ Peer Review Accepted ]

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© Copyright © 2020 Adams, Miyazaki, Watanabe, Ohkama-Ohtsu, Seo and Shin. Phytoremediation is optimized when plants grow vigorously while accumulating the contaminant of interest. Here we show that sulphur supply alleviates aerial chlorosis and growth retardation caused by cesium stress without reducing cesium accumulation in Arabidopsis thaliana. This alleviation was not due to recovery of cesium-induced potassium decrease in plant tissues. Sulphur supply also alleviated sodium stress but not potassium deficiency stress. Cesium-induced root growth inhibition has previously been demonstrated as being mediated through jasmonate biosynthesis and signalling but it was found that sulphur supply did not decrease the levels of jasmonate accumulation or jasmonate-responsive transcripts. Instead, induction of a glutathione synthetase gene GSH2 and reduction of a phytochelatin synthase gene PCS1 as well as increased accumulation of glutathione and cysteine were observed in response to cesium. Exogenous application of glutathione or concomitant treatments of its biosynthetic intermediates indeed alleviated cesium stress. Interestingly, concomitant treatments of glutathione biosynthetic intermediates together with a glutathione biosynthesis inhibitor did not cancel the alleviatory effects against cesium suggesting the existence of a glutathione-independent pathway. Taken together, our findings demonstrate that plants exposed to cesium increase glutathione accumulation to alleviate the deleterious effects of cesium and that exogenous application of sulphur-containing compounds promotes this innate process.

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A role for auxin signaling in the acquisition of longevity during seed maturation

Anthoni Pellizzaro, Martine Neveu, David Lalanne, Benoit Ly Vu, Yuri Kanno, Mitsunori Seo, Olivier Leprince, Julia Buitink

New Phytologist   225 ( 1 ) 284 - 296   2020.01 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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© 2019 INRA New Phytologist © 2019 New Phytologist Trust Seed longevity, the maintenance of viability during dry storage, is a crucial factor to preserve plant genetic resources and seed vigor. Inference of a temporal gene-regulatory network of seed maturation identified auxin signaling as a putative mechanism to induce longevity-related genes. Using auxin-response sensors and tryptophan-dependent auxin biosynthesis mutants of Arabidopsis thaliana L., the role of auxin signaling in longevity was studied during seed maturation. DII and DR5 sensors demonstrated that, concomitant with the acquisition of longevity, auxin signaling input and output increased and underwent a spatiotemporal redistribution, spreading throughout the embryo. Longevity of seeds of single auxin biosynthesis mutants with altered auxin signaling activity was affected in a dose–response manner depending on the level of auxin activity. Longevity-associated genes with promoters enriched in auxin response elements and the master regulator ABSCISIC ACID INSENSITIVE3 were induced by auxin in developing embryos and deregulated in auxin biosynthesis mutants. The beneficial effect of exogenous auxin during seed maturation on seed longevity was abolished in abi3-1 mutants. These data suggest a role for auxin signaling activity in the acquisition of longevity during seed maturation.

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Transcriptomics of cytokinin and auxin metabolism and signaling genes during seed maturation in dormant and non-dormant wheat genotypes

Pham Anh Tuan, Yuji Yamasaki, Yuri Kanno, Mitsunori Seo, Belay T. Ayele

Scientific Reports   9 ( 1 )   2019.12 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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© 2019, The Author(s). To gain insights into the roles of cytokinin (CK) and auxin in regulating dormancy during seed maturation in wheat, we examined changes in the levels of CK and indole-3-acetic acid (IAA) and expression patterns of their metabolism and signaling genes in embryonic and endospermic tissues of dormant and non-dormant genotypes. Seed maturation was associated with a decrease in the levels of isopentenyladenine in both tissues mainly via repression of the CK biosynthetic TaLOG genes. Differential embryonic trans-zeatin content and expression patterns of the CK related genes including TacZOG, TaGLU and TaARR12 between maturing seeds of the two genotypes implicate CK in the control of seed dormancy induction and maintenance. Seed maturation induced a decrease of IAA level in both tissues irrespective of genotype, and this appeared to be mediated by repression of specific IAA biosynthesis, transport and IAA-conjugate hydrolysis genes. The differential embryonic IAA content and expression pattern of the IAA biosynthetic gene TaAO during the early stage of seed maturation between the two genotypes imply the role of IAA in dormancy induction. It appears from our data that the expression of specific auxin signaling genes including TaRUB, TaAXR and TaARF mediate the role of auxin signaling in dormancy induction and maintenance during seed maturation in wheat.

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Whole Irradiated Plant Leaves Showed Faster Photosynthetic Induction Than Individually Irradiated Leaves via Improved Stomatal Opening

Shunji Shimadzu, Mitsunori Seo, Ichiro Terashima, Wataru Yamori

Frontiers in Plant Science   10   2019.11 [ Peer Review Accepted ]

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© Copyright © 2019 Shimadzu, Seo, Terashima and Yamori. Rapid photosynthetic induction is crucial for plants under fluctuating light conditions in a crop canopy as well as in an understory. Most previous studies have focused on photosynthetic induction responses in a single leaf, whereas the systemic responses of the whole plant have not been considered. In a natural environment, however, both single leaves and whole plants are exposed to sunlight, since the light environment is not uniform even within a given plant. In the present study, we examined whether there is any difference between the photosynthetic induction response of a leaf of a whole irradiated plant and an individually irradiated leaf in Arabidopsis thaliana to consider photosynthetic induction as the response of a whole plant. We used two methods, the visualization of photosynthesis and direct measurements of gas-exchange and Chl fluorescence, to demonstrate that whole irradiated plant promoted its photosynthetic induction via improved stomatal opening compared with individually irradiated leaf. Furthermore, using two Arabidopsis knockout mutants of abscisic acid transporter, abcg25 and abcg40, the present study suggests that abscisic acid could be involved in this systemic response for stomatal opening, allowing plants to optimize the use of light energy at minimal cost in plants in a dynamic light environment.

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Transcriptome Analysis of the Hierarchical Response of Histone Deacetylase Proteins That Respond in an Antagonistic Manner to Salinity Stress

Minoru Ueda, Akihiro Matsui, Shunsuke Watanabe, Makoto Kobayashi, Kazuki Saito, Maho Tanaka, Junko Ishida, Miyako Kusano, Mitsunori Seo, Motoaki Seki

Frontiers in Plant Science   10   2019.10 [ Peer Review Accepted ]

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© Copyright © 2019 Ueda, Matsui, Watanabe, Kobayashi, Saito, Tanaka, Ishida, Kusano, Seo and Seki. Acetylation in histone and non-histone proteins is balanced by histone acetyltransferase and histone deacetylase (HDAC) enzymatic activity, an essential aspect of fine-tuning plant response to environmental stresses. HDACs in Arabidopsis are composed of three families (RPD3-like, SIRT, and HD-tuins). A previous study indicated that class I (HDA19) and class II (HDA5/14/15/18) RPD3-like family HDACs control positive and negative responses to salinity stress, respectively. Furthermore, quintuple hda5/14/15/18/19 mutants (quint) exhibit salinity stress tolerance, suggesting that hda19 suppresses the sensitivity to salinity stress present in quadruple hda5/14/15/18 mutants (quad). In the present study, transcriptome analysis of the quint mutant was conducted to elucidate the hierarchical control of salinity stress response operated by RPD3-like family HDACs (HDA5/14/15/18/19). The analysis identified 4,832 salt-responsive genes in wild-type (Col-0), hda19-3, quad, and quint plants and revealed that 56.7% of the salt-responsive genes exhibited a similar expression pattern in both the hda19-3 and quint plants. These results indicate that deficiency in HDA19 has a bigger impact on salinity stress response than in class II HDACs. Furthermore, the expression pattern of genes encoding enzymes that metabolize phytohormones raises the possibility that a drastic change in the homeostasis of phytohormones, such as abscisic acid, brassinosteroid, and gibberellin, may contribute to increasing stress tolerance in hda19-3 and quint plants. Among these phytohormones, abscisic acid accumulation actually increased in hda19-3 and quint plants, and decreased in quad, compared with wild-type plants. Importantly, 7.8% of the salt-responsive genes in quint plants exhibited a similar expression pattern in quad plants, suggesting that some gene sets are regulated in an HDA5/14/15/18-dependent manner. The transcriptome analysis conducted in the present study revealed the hierarchical and independent regulation of salt stress response that is mediated through HDA19 and class II HDACs.

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Acetic acid treatment enhances drought avoidance in cassava (Manihot esculenta crantz)

Yoshinori Utsumi, Chikako Utsumi, Maho Tanaka, Chien Van Ha, Satoshi Takahashi, Akihiro Matsui, Tomoko M. Matsunaga, Sachihiro Matsunaga, Yuri Kanno, Mitsunori Seo, Yoshie Okamoto, Erika Moriya, Motoaki Seki

Frontiers in Plant Science   10   2019.04 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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© 2019 Utsumi, Utsumi, Tanaka, Ha, Takahashi, Matsui, Matsunaga, Matsunaga, Kanno, Seo, Okamoto, Moriya and Seki. The external application of acetic acid has recently been reported to enhance survival of drought in plants such as Arabidopsis, rapeseed, maize, rice, and wheat, but the effects of acetic acid application on increased drought tolerance in woody plants such as a tropical crop “cassava" remain elusive. A molecular understanding of acetic acid-induced drought avoidance in cassava will contribute to the development of technology that can be used to enhance drought tolerance, without resorting to transgenic technology or advancements in cassava cultivation. In the present study, morphological, physiological, and molecular responses to drought were analyzed in cassava after treatment with acetic acid. Results indicated that the acetic acid-treated cassava plants had a higher level of drought avoidance than water-treated, control plants. Specifically, higher leaf relative water content, and chlorophyll and carotenoid levels were observed as soils dried out during the drought treatment. Leaf temperatures in acetic acid-treated cassava plants were higher relative to leaves on plants pretreated with water and an increase of ABA content was observed in leaves of acetic acid-treated plants, suggesting that stomatal conductance and the transpiration rate in leaves of acetic acid-treated plants decreased to maintain relative water contents and to avoid drought. Transcriptome analysis revealed that acetic acid treatment increased the expression of ABA signaling-related genes, such as OPEN STOMATA 1 (OST1) and protein phosphatase 2C; as well as the drought response and tolerance-related genes, such as the outer membrane tryptophan-rich sensory protein (TSPO), and the heat shock proteins. Collectively, the external application of acetic acid enhances drought avoidance in cassava through the upregulation of ABA signaling pathway genes and several stress responses- and tolerance-related genes. These data support the idea that adjustments of the acetic acid application to plants is useful to enhance drought tolerance, to minimize the growth inhibition in the agricultural field.

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Cell cycle inhibitors improve seed storability after priming treatments

Naoto Sano, Mitsunori Seo

Journal of Plant Research   132 ( 2 ) 263 - 271   2019.03 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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© 2019, The Botanical Society of Japan and Springer Japan KK, part of Springer Nature. Seed priming is a treatment that controls seed water content to partially activate germination processes such as metabolism but prevents full germination of the seeds. The treatment is well known to enhance seed performance, including germination, but sometimes reduces seed storability or longevity as a side effect. Toward developing a novel priming technique that can maintain seed longevity for a longer time period, chemicals that suppress the seed deterioration under a controlled condition were screened from 80 known biologically active compounds contained in the RIKEN NPDepo authentic library using Arabidopsis thaliana seeds. Seeds primed with mimosine, a cell cycle inhibitor, retained higher survival rate after a controlled deterioration treatment compared to seeds primed without the chemical. In addition, other cell cycle inhibitors such as aphidicolin, hydroxyurea and oryzalin had similar effects on the seed storability after priming. Our results suggest that progression of the cell cycle during priming is an important checkpoint that determines the storability of seeds after the treatment.

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Developmental analysis of the early steps in strigolactone-mediated axillary bud dormancy in rice

Le Luo, Megumu Takahashi, Hiromu Kameoka, Ruyi Qin, Toshihide Shiga, Yuri Kanno, Mitsunori Seo, Masaki Ito, Guohua Xu, Junko Kyozuka

Plant Journal   97 ( 6 ) 1006 - 1021   2019.03 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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© 2019 The Authors. The Plant Journal published by John Wiley & Sons Ltd and Society for Experimental Biology. By contrast with rapid progress in understanding the mechanisms of biosynthesis and signaling of strigolactone (SL), mechanisms by which SL inhibits axillary bud outgrowth are less well understood. We established a rice (Oryza sativa L.) hydroponic culture system to observe axillary buds at the critical point when the buds enter the dormant state. In situ hybridization analysis indicated that cell division stops in the leaf primordia of the buds entering dormancy. We compared transcriptomes in the axillary buds isolated by laser capture microdissection before and after entering the dormant state and identified genes that are specifically upregulated or downregulated in dormant buds respectively, in SL-mediated axillary bud dormancy. Typically, cell cycle genes and ribosomal genes are included among the active genes while abscisic acid (ABA)-inducible genes are among the dormant genes. Application of ABA to the hydroponic culture suppressed the growth of axillary buds of SL mutants to the same level as wild-type (WT) buds. Tiller number was decreased in the transgenic lines overexpressing OsNCED1, the gene that encodes ABA biosynthesis enzyme. These results indicated that the main site of SL function is the leaf primordia in the axillary bud and that ABA is involved in SL-mediated axillary bud dormancy.

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Arabidopsis molybdenum cofactor sulfurase ABA3 contributes to anthocyanin accumulation and oxidative stress tolerance in ABA-dependent and independent ways

Shunsuke Watanabe, Muneo Sato, Yuji Sawada, Maho Tanaka, Akihiro Matsui, Yuri Kanno, Masami Yokota Hirai, Motoaki Seki, Atsushi Sakamoto, Mitsunori Seo

Scientific Reports   8 ( 1 )   2018.12 [ Peer Review Accepted ]

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© 2018, The Author(s). Arabidopsis ABA3 is an enzyme involved in the synthesis of the sulfurated form of the molybdenum (Mo) cofactor (MoCo), which is required for the enzymatic activity of so-called Mo enzymes such as aldehyde oxidase (AO) and xanthine dehydrogenase (XDH). It has been reported that AO and XDH are essential for the biosynthesis of the bioactive compounds, ABA and allantoin, respectively. However, aba3 mutants often exhibit pleiotropic phenotypes that are not explained by defects in ABA and/or allantoin biosynthesis, leading us to hypothesize that ABA3 regulates additional metabolic pathways. To reveal the currently unidentified functions of ABA3 we compared transcriptome and metabolome of the Arabidopsis aba3 mutant with those of wild type and a typical ABA-deficient mutant aba2. We found that endogenous levels of anthocyanins, members of the flavonoid group, were significantly lower in the aba3 mutant than in the wild type or the aba2 mutant under oxidative stress. In contrast, mutants defective in the AO and XDH holoenzymes accumulated significantly higher levels of anthocyanins when compared with aba3 mutant under the same conditions. Our findings shed light on a key role of ABA3 in the ABA- and allantoin-independent accumulation of anthocyanins during stress responses.

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Arabidopsis thaliana NGATHA1 transcription factor induces ABA biosynthesis by activating NCED3 gene during dehydration stress

Hikaru Sato, Hironori Takasaki, Fuminori Takahashi, Takamasa Suzuki, Satoshi Iuchi, Nobutaka Mitsuda, Masaru Ohme-Takagi, Miho Ikeda, Mitsunori Seo, Kazuko Yamaguchi-Shinozaki, Kazuo Shinozaki

Proceedings of the National Academy of Sciences of the United States of America   115 ( 47 ) E11178 - E11187   2018.11 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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© 2018 National Academy of Sciences. All Rights Reserved. The plant hormone abscisic acid (ABA) is accumulated after drought stress and plays critical roles in the responses to drought stress in plants, such as gene regulation, stomatal closure, seed maturation, and dormancy. Although previous reports revealed detailed molecular roles of ABA in stress responses, the factors that contribute to the drought-stress responses—in particular, regulation of ABA accumulation—remain unclear. The enzyme NINE-CIS-EPOXYCAROTENOID DIOXYGENASE 3 (NCED3) is essential for ABA biosynthesis during drought stress, and the NCED3 gene is highly induced by drought stress. In the present study, we isolated NGATHAs (NGAs) as candidate transcriptional regulators of NCED3 through a screen of a plant library harboring the transcription factors fused to a chimeric repressor domain, SRDX. The NGA proteins were directly bound to a cis-element NGA-binding element (NBE) in the 5′ untranslated region (5′ UTR) of the NCED3 promoter and were suggested to be transcriptional activators of NCED3. Among the single-knockout mutants of four NGA family genes, we found that the NGATHA1 (NGA1) knockout mutant was drought-stress-sensitive with a decreased expression level of NCED3 during dehydration stress. These results suggested that NGA1 essentially functions as a transcriptional activator of NCED3 among the NGA family proteins. Moreover, the NGA1 protein was degraded under nonstressed conditions, and dehydration stress enhanced the accumulation of NGA1 proteins, even in ABA-deficient mutant plants, indicating that there should be ABA-independent posttranslational regulations. These findings emphasize the regulatory mechanisms of ABA biosynthesis during early drought stress.

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ABA transport and Plant water stress responses

Takashi Kuromori, Mitsunori Seo, Kazuo Shinozaki

Trends in Plant Science   23   513 - 522   2018 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

RNA-Seq using bulked recombinant inbred line populations uncovers the importance of brassinosteroid for seed longevity after priming treatments

Naoto Sano, June Sik Kim, Yoshihiko Onda, Takahito Nomura, Keiichi Mochida, Masanori Okamoto, Mitsunori Seo

Scientific Reports   7 ( 1 )   2017.12 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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© 2017 The Author(s). Seed priming is a commercially used technique for improving seed performance including germination. However, the treatment sometimes reduces seed longevity as a side effect, limiting the storable period or longevity of the seeds. To overcome this problem, molecular mechanisms involved in the loss of seed longevity during priming were analyzed using natural variations of Arabidopsis thaliana. We found that the Est-1 accession retained longevity for longer after priming compared to the reference accession Col-0. QTL analysis using 279 recombinant inbred lines (RILs) derived from the Est-1 × Col-0 detected three QTL regions associated with the loss of seed longevity during priming. Bulked transcriptome analysis (RNA-Seq with bulked RIL populations) revealed that genes related to brassinosteroid (BR) biosynthesis/signaling and cell wall modification were highly expressed in primed seeds with shorter longevity. After priming, BR-deficient mutants cyp85a1/a2 and det2 showed significantly longer longevity than the wild type (WT). Moreover, tetrazolium staining indicated that mutant seed coats were less permeable after priming than those of WT. We suggest that the loss of seed longevity in primed seed is due to increased seed coat permeability, which is positively regulated, at least partly, via BR signaling.

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