Strigolactones (SLs) are phytohormones that inhibit shoot branching and function in the rhizospheric communication with symbiotic fungi and parasitic weeds. An a/b-hydrolase protein, DWARF14 (D14), has been recognized to be an essential component of plant SL signalling, although its precise function remains unknown. Here we present the SL-dependent interaction of D14 with a gibberellin signalling repressor SLR1 and a possible mechanism of phytohormone perception in D14-mediated SL signalling. D14 functions as a cleavage enzyme of SLs, and the cleavage reaction induces the interaction with SLR1. The crystal structure of D14 shows that 5-hydroxy-3-methylbutenolide (D-OH), which is a reaction product of SLs, is trapped in the catalytic cavity of D14 to form an altered surface. The D14 residues recognizing D-OH are critical for the SL-dependent D14 À SLR1 interaction. These results provide new insight into crosstalk between gibberellin and SL signalling pathways.

Protein knockdown using the auxin-inducible degron (AID) technology is useful to study protein function in living cells because it induces rapid depletion, which makes it possible to observe an immediate phenotype. However, the current AID system has two major drawbacks: leaky degradation and the requirement for a high dose of auxin. These negative features make it difficult to control precisely the expression level of a protein of interest in living cells and to apply this method to mice. Here, we overcome these problems by taking advantage of a bump-and-hole approach to establish the AID version 2 (AID2) system. AID2, which employs an OsTIR1(F74G) mutant and a ligand, 5-Ph-IAA, shows no detectable leaky degradation, requires a 670-times lower ligand concentration, and achieves even quicker degradation than the conventional AID. We demonstrate successful generation of human cell mutants for genes that were previously difficult to deal with, and show that AID2 achieves rapid target depletion not only in yeast and mammalian cells, but also in mice.

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Inactivation of the phytohormone auxin plays important roles in plant development, and several enzymes have been implicated in auxin inactivation. In this study, we show that the predominant natural auxin, indole-3-acetic acid (IAA), is mainly inactivated via the GH3-ILR1-DAO pathway. IAA is first converted to IAA-amino acid conjugates by GH3 IAA-amidosynthetases. The IAA-amino acid conjugates IAA-aspartate (IAA-Asp) and IAA-glutamate (IAA-Glu) are storage forms of IAA and can be converted back to IAA by ILR1/ILL amidohydrolases. We further show that DAO1 dioxygenase irreversibly oxidizes IAA-Asp and IAA-Glu into 2-oxindole-3-acetic acid-aspartate (oxIAA-Asp) and oxIAA-Glu, which are subsequently hydrolyzed by ILR1 to release inactive oxIAA. This work established a complete pathway for the oxidative inactivation of auxin and defines the roles played by auxin homeostasis in plant development.

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Strigolactones (SLs) are a novel class of plant hormones and rhizosphere communication signals, although the molecular mechanisms underlying their activities have not yet been fully determined. Nor is their application in agriculture well developed. The importance of plant hormone agonists has been demonstrated in both basic and applied research, and chemicals that mimic strigolactone functions should greatly facilitate strigolactone research. Here, we report our discovery of a new phenoxyfuranone compound, 4-Br debranone (4BD), that shows similar activity to that of the major strigolactone (SL) analog GR24 in many aspects of a biological assay on plants. 4BD strongly inhibited tiller bud outgrowth in the SL-deficient rice mutant d10 at the same concentration as GR24, with no adverse effects, even during prolonged cultivation. This result was also observed in the Arabidopsis thaliana SL-deficient mutants max1, max3, and max4. However, the application of 4BD to the Arabidopsis SL-insensitive mutant max2 induced no morphological changes in it. The expression of SL biosynthetic genes was also reduced by 4BD treatment, probably via negative feedback regulation. However, in a seed germination assay on Striga hermonthica, a root parasitic plant, 4BD showed far less activity than GR24. These results suggest that 4BD is the first plant-specific strigolactone mimic.

A silver/DBU catalyst system was developed for the effective synthesis of cyclic carbonate and oxazolidinone from the reaction of CO 2 with propargylic alcohols and propargylic amines, respectively, in high yields under mild conditions. It was found that the [3,3]-sigmatropic MeyerSchuster-type rearrangement of the propargylic alcohol was mediated by CO 2 in DMF to afford the corresponding ¡,¢-unsaturated carbonyl compounds in high yields. The silver salt combined with the chiral Schiff base ligand could be applied to enantioselective chemical CO 2 incorporation into various bispropargylic alcohols to produce the corresponding cyclic carbonate in high yields with high enantioselectivity. The absolute configuration was determined by VCD spectroscopy as well as by X-ray analysis. These products were found to be active for the aminolysis reaction to afford the corresponding carbamate derivatives in high yields without any loss of optical purity.An enormous amount of energy has been generated by the oxidation of hydrocarbons in order to make our life comfortable and convenient while generating an enormous amount of CO 2 worldwide.1 Because the most oxidized form of the carbon derivatives is much less reactive, its application to organic synthesis has been considered to be one of the most challenging research topics. As well as the chemical fixation of CO 2 , much effort has been made to utilize CO 2 as an attractive C1 feedstock for organic synthesis due to its ubiquitous, abundant, and nontoxic properties, however due to its lower reactivity, harsh reaction conditions are required to activate and incorporate CO 2 into organic compounds.2 It is necessary to develop a mild reaction system including catalysts to efficiently capture CO 2 into a wide variety of substrates, especially fine-chemicals. Various synthetic reactions of CO 2 have been reported. Typically enol derivatives, 3 Grignard reagents, 4 and alkyllithium compounds 5 readily react with CO 2 to afford the corresponding carboxylic acids, though a stoichiometric amount of a strong nucleophile is employed. Transition-metals, such as nickel, 6 rhodium, 7 palladium, 8 copper, 2e,9 and gold, 2e can catalyze the reaction of CO 2 to produce the corresponding carboxylic acid and lactone derivatives. However, it is required to prepare in advance reactants containing a boron, halogen moiety, etc., and the scope and applicability are limited.It was recently found that a catalytic amount of a silver salt as a ³-Lewis acid to activate an alkyne combined with the use of DBU is an efficient catalyst system for the reaction of CO 2 with propargylic derivatives. We now report that a silver salt/DBU combination catalyzes the reaction of CO 2 with propargylic alcohols 10a and propargylic amines 10b to produce the corresponding cyclic carbonates and oxazolidinones in good to excellent yields, respectively. We also describe that a MeyerSchuster-type rearrangement is mediated by CO 2 in the presence of a catalytic amount of silver methanesulfonate and a base to afford the corre...

The combined catalyst system of silver acetate with a chiral Schiff base ligand achieved asymmetric carbon dioxide incorporation into bispropargylic alcohols with desymmetrization to afford the corresponding cyclic carbonates with good-to-excellent enantiomeric excesses.