Abscisic acid (ABA) signaling is important for stress responses and developmental processes in plants. A subgroup of protein phosphatase 2C (group A PP2C) or SNF1-related protein kinase 2 (subclass III SnRK2) have been known as major negative or positive regulators of ABA signaling, respectively. Here, we demonstrate the physical and functional linkage between these two major signaling factors. Group A PP2Cs interacted physically with SnRK2s in various combinations, and efficiently inactivated ABA-activated SnRK2s via dephosphorylation of multiple Ser/Thr residues in the activation loop. This step was suppressed by the RCAR/PYR ABA receptors in response to ABA. However the abi1-1 mutated PP2C did not respond to the receptors and constitutively inactivated SnRK2. Our results demonstrate that group A PP2Cs act as 'gatekeepers' of subclass III SnRK2s, unraveling an important regulatory mechanism of ABA signaling.A s sessile organisms, plants have to rapidly recognize and adapt to environmental changes. The phytohormone abscisic acid (ABA) plays a central role in such responses (1, 2), and is also involved in many developmental processes (3) and defense systems (4). Thus, ABA functions as a key molecule that unifies and regulates biotic and abiotic stress responses and the developmental status of the plant. Hence, the biological and agricultural importance of ABA has led to extensive studies on its signaling mechanism, and many putative signal transducers have been reported (5). Although it has been difficult to integrate all of the current findings, significant progress was recently made by two independent research groups. They identified the RCAR/ PYR family proteins as ABA receptors that inhibit protein phosphatase 2C (PP2C) in an ABA-dependent manner (6, 7). Among plant PP2Cs, a group A subfamily (e.g., ABI1 and ABI2) is annotated as negative regulators of the ABA response in seeds through to adult plants (5). Such PP2C-dependent negative regulation can be canceled by RCAR/PYR in response to ABA, leading to activation of some positive regulatory pathways (6, 7). Previously, we demonstrated that ABI1 interacts with a protein kinase, SRK2E (OST1/SnRK2.6) (8). SRK2E belongs to the SNF1-related protein kinase 2 (SnRK2) family, which is activated by ABA or osmotic stress and positively regulates the ABA response in various tissues (9 -11). Furthermore, ABAdependent activation of SRK2E was repressed in an abi1-1 mutant, suggesting that SnRK2 functions downstream of PP2C (8, 9). Based on these findings, a model was hypothesized in which RCAR/PYR and PP2C negatively regulate SnRK2 (7). However, there is no direct evidence demonstrating how PP2C regulates SnRK2, and the molecular process between them remains a question in ABA signaling. Our presented data clearly demonstrated the biochemical relation between PP2C and SnRK2 and elucidated an important regulatory mechanism of ABA signaling. Results and DiscussionRequirement of SnRK2 Activity for ABA Responses. In Arabidopsis, subclass III of the SnRK2 family is composed of...

The hydrolysis of cellulose into saccharides using a range of solid catalysts is investigated for potential application in the environmentally benign saccharification of cellulose. Crystalline pure cellulose is not hydrolyzed by conventional strong solid Brønsted acid catalysts such as niobic acid, H-mordenite, Nafion and Amberlyst-15, whereas amorphous carbon bearing SO 3H, COOH, and OH function as an efficient catalyst for the reaction. The apparent activation energy for the hydrolysis of cellulose into glucose using the carbon catalyst is estimated to be 110 kJ mol (-1), smaller than that for sulfuric acid under optimal conditions (170 kJ mol (-1)). The carbon catalyst can be readily separated from the saccharide solution after reaction for reuse in the reaction without loss of activity. The catalytic performance of the carbon catalyst is attributed to the ability of the material to adsorb beta-1,4 glucan, which does not adsorb to other solid acids.

The production of diesel from vegetable oil calls for an efficient solid catalyst to make the process fully ecologically friendly. Here we describe the preparation of such a catalyst from common, inexpensive sugars. This high-performance catalyst, which consists of stable sulphonated amorphous carbon, is recyclable and its activity markedly exceeds that of other solid acid catalysts tested for 'biodiesel' production.

Niobic acid, Nb(2)O(5)·nH(2)O, has been studied as a heterogeneous Lewis acid catalyst. NbO(4) tetrahedra, Lewis acid sites, on Nb(2)O(5)·nH(2)O surface immediately form NbO(4)-H(2)O adducts in the presence of water. However, a part of the adducts can still function as effective Lewis acid sites, catalyzing the allylation of benzaldehyde with tetraallyl tin and the conversion of glucose into 5-(hydroxymethyl)furfural in water.

Carbonization of d-glucose at 573−723 K followed by sulfonation produces a functionalized amorphous carbon material with acid catalytic activity as a solid-acid replacement for sulfuric acid. The carbon material contains phenolic hydroxyl, carboxylic acid, and sulfonic acid groups and exhibits high catalytic performance for liquid-phase acid-catalyzed reactions. Carbonization at higher temperature followed by sulfonation also results in amorphous carbon, but the resultant does not exhibit catalytic activity although the amorphous carbon has sufficient amount of sulfonic acid groups. Structural and active site analyses suggest that the marked difference in catalytic activity is due to the accessibility of reactants to sulfonic acid groups in the carbon structure.

Solid acids are conventional materials that have wide applications in chemical production, separation/purification, and polymer-electrolyte fuel-cell (PEFC) technologies, and the chemical industry is currently searching for a highly active and stable solid acid to improve the environmental safety of the production of chemicals and energy. Over 15 million tons of sulfuric acid is annually consumed as "an unrecyclable catalyst"-which requires costly and inefficient separation of the catalyst from homogeneous reaction mixtures-for the production of industrially important chemicals, thus resulting in a huge waste of energy and large amounts of waste products. The "green" approach to chemical processes has stimulated the use of recyclable strong solid acids as replacements for such unrecyclable "liquid acid" catalysts. [1][2][3][4] Thermostable strong solid acids would have genuine applications in PEFCs as proton conductors, for improving fuel efficiency, and for reducing the use of noble-metal catalysts by increasing the working temperature.[5] However, a major obstacle to such progress is the lack of a solid acid that is as active, stable, and inexpensive as sulfuric acid.An ideal solid material for the applications considered here should have high stability and numerous strong protonic acid sites. It is essential for the solid acid to maintain strong acidity even in water since water participates in fuel-cell reactions and many industrially important acid-catalyzed reactions. While organic acid/inorganic solid oxide hybrids and strong acidic cation-exchangeable resins, including perfluorosulfonated ionomers (for example, nafion), have been studied extensively as promising approaches for the construction of desired solid acids or proton conductors, [6] such materials are expensive and the acid activities are still much lower than that of sulfuric acid.[3] These drawbacks have limited their practical utility. Herein, we report the synthesis of a carbon-based solid acid with a high density of sulfonic acid groups (SO 3 H) and discuss its performance as a novel strong and stable solid acid. Here, a new strategy is adopted for the development of new types of solid acid: a carbon material is obtained by incomplete carbonization of sulfoaromatic hydrocarbons and consists of small polycyclic aromatic carbon sheets with attached SO 3 H groups. This approach is simple and allows for the use of sulfoaromatic hydrocarbons-strong, stable solvent-soluble acids (for example, benzene sulfonic acid and naphthalene sulfonic acid)-as insoluble solid acids.Such carbon-based solid acids can be readily prepared by heating aromatic compounds such as naphthalene in sulfuric acid at 473-573 K. [7] In this synthesis, the sulfonation of the aromatic compounds is the first stage of the reaction. The resulting sulfonated aromatic compounds are incompletely carbonized, which results in the formation of a solid with a nominal sample composition of CH 0.35 O 0.35 S 0.14 . The total yield of the product based on carbon is about 55 % by this metho...

Pentatricopeptide repeat (PPR) proteins are eukaryotic RNA-binding proteins that are commonly found in plants. Organelle transcript processing and stability are mediated by PPR proteins in a gene-specific manner through recognition by tandem arrays of degenerate 35-amino-acid repeating units, the PPR motifs. However, the sequence-specific RNA recognition mechanism of the PPR protein remains largely unknown. Here, we show the principle underlying RNA recognition for PPR proteins involved in RNA editing. The distance between the PPR-RNA alignment and the editable C was shown to be conserved. Amino acid variation at 3 particular positions within the motif determined recognition of a specific RNA in a programmable manner, with a 1-motif to 1-nucleotide correspondence, with no gap sequence. Data from the decoded nucleotide frequencies for these 3 amino acids were used to assign accurate interacting sites to several PPR proteins for RNA editing and to predict the target site for an uncharacterized PPR protein.

Two-dimensional metal oxide sheets in HTiNbO(5) and HSr(2)Nb(3)O(10), cation-exchangeable layered metal oxides, were examined as solid acid catalysts. Exfoliation of HTiNbO(5) and HSr(2)Nb(3)O(10) in aqueous solutions formed colloidal single-crystal TiNbO(5)(-) and Sr(2)Nb(3)O(10)(-) nanosheets, which precipitated under an acidic condition to form aggregates of HTiNbO(5) nanosheets and HSr(2)Nb(3)O(10) nanosheets. Although esterification of acetic acid, cracking of cumene, and dehydration of 2-propanol were not catalyzed by original HTiNbO(5) because of the narrow interlayer distance, which prevents the insertion of organic molecules, HTiNbO(5) nanosheets functioned as a strong solid acid catalyst for the reactions. Nanosheets of HSr(2)Nb(3)O(10) exhibited no or slight catalytic activity for these reactions. NH(3) temperature-programmed desorption and (1)H magic-angle spinning nuclear magnetic resonance spectroscopy revealed that HTiNbO(5) nanosheets have strong Brønsted acid sites, whereas HSr(2)Nb(3)O(10) nanosheets do not.