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Mikihisa Umehara

Bio: Mikihisa Umehara is an academic researcher from Toyo University. The author has contributed to research in topics: Strigolactone & Somatic embryogenesis. The author has an hindex of 19, co-authored 44 publications receiving 3837 citations. Previous affiliations of Mikihisa Umehara include University of Tsukuba & University of Tokyo.

Papers
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Journal ArticleDOI
11 Sep 2008-Nature
TL;DR: It is proposed that strigolactones act as a new hormone class—or their biosynthetic precursors—in regulating above-ground plant architecture, and also have a function in underground communication with other neighbouring organisms.
Abstract: Shoot branching is a major determinant of plant architecture and is highly regulated by endogenous and environmental cues. Two classes of hormones, auxin and cytokinin, have long been known to have an important involvement in controlling shoot branching. Previous studies using a series of mutants with enhanced shoot branching suggested the existence of a third class of hormone(s) that is derived from carotenoids, but its chemical identity has been unknown. Here we show that levels of strigolactones, a group of terpenoid lactones, are significantly reduced in some of the branching mutants. Furthermore, application of strigolactones inhibits shoot branching in these mutants. Strigolactones were previously found in root exudates acting as communication chemicals with parasitic weeds and symbiotic arbuscular mycorrhizal fungi. Thus, we propose that strigolactones act as a new hormone class-or their biosynthetic precursors-in regulating above-ground plant architecture, and also have a function in underground communication with other neighbouring organisms.

1,742 citations

Journal ArticleDOI
TL;DR: Evidence is provided that DWARF14 (D14) inhibits rice tillering and may act as a new compo-nent of the strigolactone-dependent branching inhibition pathway and it is proposed that D14 functions downstream of striglactone synthesis, as a component of hormone signaling or as an enzyme that participates in the conversion of strIGolactones to the bioactive form.
Abstract: Recent studies using highly branched mutants of pea, Arabidopsis and rice have demonstrated that strigolactones, a group of terpenoid lactones, act as a new hormone class, or its biosynthetic precursors, in inhibiting shoot branching. Here, we provide evidence that DWARF14 (D14) inhibits rice tillering and may act as a new compo-nent of the strigolactone-dependent branching inhibition pathway. The d14 mutant exhibits increased shoot branch-ing with reduced plant height like the previously characterized strigolactone-deficient and -insensitive mutants d10 and d3, respectively. The d10-1 d14-1 double mutant is phenotypically indistinguishable from the d10-1 and d14-1 single mutants, consistent with the idea that D10 and D14 function in the same pathway. However, unlike with d10, the d14 branching phenotype could not be rescued by exogenous strigolactones. In addition, the d14 mutant contained a higher level of 2'-epi-5-deoxystrigol than the wild type. Positional cloning revealed that D14 encodes a protein of the alpha/beta-fold hydrolase superfamily, some members of which play a role in metabolism or signaling of plant hormones. We propose that D14 functions downstream of strigolactone synthesis, as a component of hormone signaling or as an enzyme that participates in the conversion of strigolactones to the bioactive form.

535 citations

Journal ArticleDOI
TL;DR: Elevated SL levels by Pi starvation contribute to the inhibition of tiller bud outgrowth in rice seedlings, and it is speculated that SL plays a dual role in the adaptation to Pi deficiency.
Abstract: Strigolactones (SLs) or SL-derived metabolite(s) have recently been shown to act as endogenous inhibitors of axillary bud outgrowth. SLs released from roots induce hyphal branching of arbuscular mycorrhizal (AM) fungi that facilitate the uptake of inorganic nutrients, such as phosphate (Pi) and nitrate, by the host plants. Previous studies have shown that SL levels in root exudates are highly elevated by Pi starvation, which might contribute to successful symbiosis with AM fungi in the rhizosphere. However, how endogenous SL levels elevated by Pi starvation contribute to its hormonal action has been unknown. Here, we show that tiller bud outgrowth in wild-type rice seedlings is inhibited, while root 2'-epi-5-deoxystrigol (epi-5DS) levels are elevated, in response to decreasing Pi concentrations in the media. However, the suppression of tiller bud outgrowth under Pi deficiency does not occur in the SL-deficient and -insensitive mutants. We also show that the responsiveness to exogenous SL is slightly increased by Pi deficiency. When Pi-starved seedlings are transferred to Pi-sufficient media, tiller bud outgrowth is induced following a decrease in root epi-5DS levels. Taken together, these results suggest that elevated SL levels by Pi starvation contribute to the inhibition of tiller bud outgrowth in rice seedlings. We speculate that SL plays a dual role in the adaptation to Pi deficiency; one as a rhizosphere signal to maximize AM fungi symbiosis for improved Pi acquisition and the other as an endogenous hormone or its biosynthetic precursor to optimize shoot branching for efficient Pi utilization.

279 citations

Journal ArticleDOI
TL;DR: It is proposed that FC1 acts as an integrator of multiple signaling pathways and is essential to the fine-tuning of shoot branching in rice.
Abstract: Recent studies of highly branched mutants of pea, Arabidopsis and rice have demonstrated that strigolactones (SLs) act as hormones that inhibit shoot branching. The identification of genes that work downstream of SLs is required for a better understanding of how SLs control the growth of axillary buds. We found that the increased tillering phenotype of fine culm1 (fc1) mutants of rice is not rescued by the application of 1 μM GR24, a synthetic SL analog. Treatment with a high concentration of GR24 (10 μM) causes suppression of tiller growth in wild-type plants, but is not effective on fc1 mutants, implying that proper FC1 functioning is required for SLs to inhibit bud growth. Overexpression of FC1 partially rescued d3-2 defects in the tiller growth and plant height. An in situ hybridization analysis showed that FC1 mRNA accumulates in axillary buds, the shoot apical meristem, young leaves, vascular tissues and the tips of crown roots. FC1 mRNA expression was not significantly affected by GR24, suggesting that transcriptional induction may not be the mechanism by which SLs affect FC1 functioning. On the other hand, the expression level of FC1 is negatively regulated by cytokinin treatment. We propose that FC1 acts as an integrator of multiple signaling pathways and is essential to the fine-tuning of shoot branching in rice.

278 citations

Journal ArticleDOI
TL;DR: It is shown that 13C-labeled CL is converted to SLs in vivo, and that endogenous CL is successfully identified from rice and Arabidopsis, demonstrating that CL is a true biosynthetic precursor for SLs.
Abstract: Strigolactones (SLs) are a class of terpenoid plant hormones that regulate shoot branching as well as being known as root-derived signals for symbiosis and parasitism. SL has tricyclic-lactone (ABC-ring) and methyl butenolide (D-ring), and they are connected through an enol ether bridge. Recently, a putative biosynthetic intermediate called carlactone (CL), of which carbon skeleton is in part similar to those of SLs, was identified by biochemical analysis of three biosynthetic enzymes, DWARF27, CAROTENOID CLEAVAGE DIOXYGENASE 7 (CCD7), and CCD8 in vitro. However, CL has never been identified from plant tissues, and the conversion of CL to SLs has not been proven in vivo. To address these questions, we chemically synthesized 13C-labeled CL. We show that 13C-labeled CL is converted to (−)-[13C]-2′-epi-5-deoxystrigol ((−)-2′-epi-5DS) and [13C]-orobanchol, endogenous SLs in rice, in the dwarf10 mutant, which is defective in CCD8. In addition, we successfully identified endogenous CL by using liquid chromatography-quadrupole/time-of-flight tandem mass spectrometry in rice and Arabidopsis. Furthermore, we determined the absolute stereochemistry of endogenous CL to be (11R)-configuration, which is the same as that of (−)-2′-epi-5DS at the corresponding position. Feeding experiments showed that only the (11R)-isomer of CL, but not the (11S)-isomer, was converted to (−)-2′-epi-5DS in vivo. Taken together, our data provide conclusive evidence that CL is an endogenous SL precursor that is stereospecifically recognized in the biosynthesis pathway.

256 citations


Cited by
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Journal ArticleDOI
TL;DR: Recent advances made in understanding the role of salicylic acid, jasmonates and ethylene in modulating plant defence responses against various diseases and pests are reviewed.
Abstract: Plant hormones play important roles in regulating developmental processes and signaling networks involved in plant responses to a wide range of biotic and abiotic stresses. Significant progress has been made in identifying the key components and understanding the role of salicylic acid (SA), jasmonates (JA) and ethylene (ET) in plant responses to biotic stresses. Recent studies indicate that other hormones such as abscisic acid (ABA), auxin, gibberellic acid (GA), cytokinin (CK), brassinosteroids (BR) and peptide hormones are also implicated in plant defence signaling pathways but their role in plant defence is less well studied. Here, we review recent advances made in understanding the role of these hormones in modulating plant defence responses against various diseases and pests.

2,072 citations

Journal ArticleDOI
TL;DR: During evolution, the genetic programme for AM has been recruited for other plant root symbioses: functional adaptation of a plant receptor kinase that is essential for AM symbiosis paved the way for nitrogen-fixing bacteria to form intracellular symbiosis with plant cells.
Abstract: Arbuscular mycorrhiza (AM), a symbiosis between plants and members of an ancient phylum of fungi, the Glomeromycota, improves the supply of water and nutrients, such as phosphate and nitrogen, to the host plant. In return, up to 20% of plant-fixed carbon is transferred to the fungus. Nutrient transport occurs through symbiotic structures inside plant root cells known as arbuscules. AM development is accompanied by an exchange of signalling molecules between the symbionts. A novel class of plant hormones known as strigolactones are exuded by the plant roots. On the one hand, strigolactones stimulate fungal metabolism and branching. On the other hand, they also trigger seed germination of parasitic plants. Fungi release signalling molecules, in the form of 'Myc factors' that trigger symbiotic root responses. Plant genes required for AM development have been characterized. During evolution, the genetic programme for AM has been recruited for other plant root symbioses: functional adaptation of a plant receptor kinase that is essential for AM symbiosis paved the way for nitrogen-fixing bacteria to form intracellular symbioses with plant cells.

1,688 citations

Journal ArticleDOI
TL;DR: This review focuses on compiling the information available on the regulation and mechanisms of root exudation processes, and provides some ideas related to the evolutionary role ofRoot exudates in shaping soil microbial communities.
Abstract: Root-secreted chemicals mediate multi-partite interactions in the rhizosphere, where plant roots continually respond to and alter their immediate environment. Increasing evidence suggests that root exudates initiate and modulate dialogue between roots and soil microbes. For example, root exudates serve as signals that initiate symbiosis with rhizobia and mycorrhizal fungi. In addition, root exudates maintain and support a highly specific diversity of microbes in the rhizosphere of a given particular plant species, thus suggesting a close evolutionary link. In this review, we focus mainly on compiling the information available on the regulation and mechanisms of root exudation processes, and provide some ideas related to the evolutionary role of root exudates in shaping soil microbial communities.

1,412 citations

Journal ArticleDOI
TL;DR: Data accumulated over the past few years now show that the UPS targets numerous intracellular regulators that have central roles in hormone signalling, the regulation of chromatin structure and transcription, tailoring morphogenesis, responses to environmental challenges, self recognition and battling pathogens.
Abstract: Plants, like other eukaryotes, rely on proteolysis to control the abundance of key regulatory proteins and enzymes. Strikingly, genome-wide studies have revealed that the ubiquitin-26S proteasome system (UPS) in particular is an exceedingly large and complex route for protein removal, occupying nearly 6% of the Arabidopsis thaliana proteome. But why is the UPS so pervasive in plants? Data accumulated over the past few years now show that it targets numerous intracellular regulators that have central roles in hormone signalling, the regulation of chromatin structure and transcription, tailoring morphogenesis, responses to environmental challenges, self recognition and battling pathogens.

1,062 citations

Journal ArticleDOI
TL;DR: Signalling pathways between plants and fungi have now been described and the identification of several novel nutrient transporters has revealed some of the cellular processes that underlie symbiosis.
Abstract: Mycorrhizal fungi are a heterogeneous group of diverse fungal taxa, associated with the roots of over 90% of all plant species. Recently, state-of-the-art molecular and genetic tools, coupled to high-throughput sequencing and advanced microscopy, have led to the genome and transcriptome analysis of several symbionts. Signalling pathways between plants and fungi have now been described and the identification of several novel nutrient transporters has revealed some of the cellular processes that underlie symbiosis. Thus, the contributions of each partner in a mycorrhizal association are starting to be unravelled. This new knowledge is now available for use in agricultural practices.

943 citations