Cyclin-Dependent Kinase Inhibitor Gene TaICK1 acts as a Potential Contributor to Wheat Male Sterility induced by a Chemical Hybridizing Agent.

Heterosis has been widely accepted as an effective strategy to increase yields in plant breeding. Notably, the chemical hybridization agent SQ-1 induces male sterility in wheat, representing a critical potential tool in hybrid seed production. However, the mechanisms underlying the male sterility induced by SQ-1 still remain poorly understood. In this study, a cyclin-dependent kinase inhibitor gene, TaICK1, which encodes a 229 amino acid protein, was identified as a potential contributor to male sterility in common wheat. The expression of TaICK1 was upregulated during the development of anthers in Xinong1376 wheat treated with SQ-1. Meanwhile, the seed setting rate was found to be significantly decreased in TaICK1 transgenic rice. Furthermore, we identified two cyclin proteins, TaCYCD2;1 and TaCYCD6;1, as interactors through yeast two-hybrid screening using TaICK1 as the bait, which were validated using bimolecular fluorescence complementation. Subcellular localization revealed that the proteins encoded by TaICK1, TaCYCD2;1, and TaCYCD6;1 were localized in the cell nucleus. The expression levels of TaCYCD2;1 and TaCYCD6;1 were lower in Xinong1376 treated with SQ-1. A further analysis demonstrated that the expression levels of OsCYCD2;1 and OsCYCD6;1 were lower in transgenic TaICK1 rice lines as well. Taken together, these results suggest that the upregulation of TaICK1, induced by SQ-1, may subsequently suppress the expression of TaCYCD2;1 and TaCYCD6;1 in anthers, resulting in male sterility. This study provides new insights into the understanding of SQ-1-induced wheat male sterility, as well as the developmental mechanisms of anthers.

Racemic synthesis and antiviral evaluation of 4'(alpha)-hydroxymethyl and 6'(alpha)-methyl substituted apiosyl nucleosides.

This article reports the novel synthesis of substituted apiosyl nucleosides. The key apiosyl intermediate 9 was constructed by sequential ozonolysis, reductions, and acetylation from the ester derivative 6. The nucleosides of uracil, thymine, cytosine, and adenine were synthesized using the glycosyl condensation procedure (silyated base and TMSOTf). The antiviral activities of the synthesized compounds against the HIV-1, HSV-1, HSV-2, and HCMV viruses were evaluated. The adenine derivative 26 showed weak anti-HIV activity (EC(50) = 10.1 microg/ml) without exhibiting any cytotoxicity up to a concentration of 100 microM.

Dihydroxyacetone variants in the organocatalytic construction of carbohydrates: mimicking tagatose and fuculose aldolases.

Dihydroxyacetone variants have been explored as donors in organocatalytic aldol reactions with various aldehyde and ketone acceptors. The protected form of dihydroxyacetone that was chosen for in-depth study was 2,2-dimethyl-1,3-dioxan-5-one, 1. Among the catalysts surveyed here, proline proved to be superior in terms of yield and stereoselectivities in the construction of various carbohydrate scaffolds. In a fashion analogous to aldolase enzymes, the de novo preparation of L-ribulose, L-lyxose, D-ribose, D-tagatose, 1-amino-1-deoxy-D-lyxitol, and other carbohydrates was accomplished via the use of 1 and proline. In reactions using 2,2-dimethyl-1,3-dioxan-5-one 1 as a donor, (S)-proline can be used as a functional mimic of tagatose aldolase, whereas (R)-proline can be regarded as an organocatalytic mimic of fuculose aldolase.

The dihydroxyacetone unit--a versatile C(3) building block in organic synthesis.

Nature employs dihydroxyacetone phosphate (DHAP) as the donor component in various enzyme-catalyzed aldol reactions. Probably the most significant example in this regard is photosynthesis, in which D-glucose, the most widespread natural product, is formed in just a few steps from DHAP. In recent years a number of synthetic equivalents of DHAP have been reported that deserve particular attention, as their applicability in organic synthesis is not limited to (stereoselective) aldol reactions. The power of these reagents has also been demonstrated convincingly in numerous other asymmetric electrophilic alpha-substitution reactions in target-oriented syntheses. Furthermore, the related 1,3-dioxins are useful equivalents of 2-substituted acrolein derivatives.

Crystal structures of dihydroxyacetone and its derivatives.

The crystal and molecular structures of three crystalline forms of the dihydroxyacetone dimer, C6H12O6, DHA-dimer: alpha (1a), beta (1b), and gamma (1c), the hydrated calcium chloride complex of dihydroxyacetone monomer, CaCl2(C3H6O3)(2) x H2O, CaCl2(DHA)2 x H2O (2a), the tetrahydrated calcium chloride complex of dihydroxyacetone monomer, CaCl2(C3H6O3) x 4H2O, CaCl2(DHA) x 4H2O (2b), the dihydroxyacetone monomer, C3H6O3, DHA (2c), and dihydroxyacetone dimethyl acetal, C5H12O4, (MeO)2DHA (3) are described. Compounds 1a and 2b crystallize in the triclinic system, and 1b,c, 2a,c, and 3 are monoclinic. Molecules of all forms of dihydroxyacetone dimer 1a,b, and 1c are the trans isomers, with the 1,4-dioxane ring in the chair conformation and the hydroxyl and hydroxymethyl groups in axial and equatorial dispositions, respectively. The Ca2+ ions in 2a and 2b are bridged by the carbonyl O atoms from two symmetry-related DHA molecules to form centrosymmetric dimers with Ca...Ca distance of 4.307(2)A in 2a and 4.330(2) and 4.305(2)A in two crystallographically independent dimers in 2b. DHA molecules coordinate to the Ca2+ ions by hydroxyl and carbonyl oxygen atoms. The eight-coordinate polyhedra of Ca2+ are completed by water molecule and Cl- ion in 2a and by four water molecules in 2b. The dihydroxyacetone molecules in 2a,b, and 2c are in an extended conformation, with both hydroxyl groups being synperiplanar (sp) to the carbonyl O atom. All hydroxyl groups in 2c (along with water molecules in 2a and 2b) are involved as donors in medium strong and weak intermolecular O-H...O hydrogen bonding. Some of them, as well as carbonyl O atoms or Cl- ions in 2a and 2b, act as acceptors in C-H...O (and C-H...Cl) hydrogen interactions.

Accumulation of sulfoquinovosyl-1-O-dihydroxyacetone in a sulfolipid-deficient mutant of Rhodobacter sphaeroides inactivated in sqdC.

The biosynthesis of the sulfolipid sulfoquinovosyl diacylglycerol in the purple bacterium Rhodobacter sphaeroides requires at least four genes:sqdA, sqdB, sqdC, and sqdD. As part of our strategy aimed at the elucidation of the function of the different sqd gene products, we insertionally inactivated sqdC of R. sphaeroides. The resulting sqdC null mutant showed only a 90% reduction in sulfolipid content. Apparently, the sqdC gene product is required for optimal sulfolipid biosynthesis, but either catalyzes no essential reaction in the pathway or can be functionally replaced to a certain extent by a different protein. The mutant accumulated a 35S-labeled compound that was purified to homogeneity from cell extracts. Matrix-assisted laser desorption mass spectrometry and nuclear magnetic resonance spectroscopy provided conclusive structural evidence to identify the compound as alpha-D-sulfoquinovosyl-1-O-dihydroxyacetone that exists in two interconvertible, keto and hemiacetal forms. Incubation of wild-type protein extracts with the labeled compound did not result in the incorporation into sulfolipid as would be expected for an intermediate of the pathway. Based on our results we propose that the sqdC gene product mediates the substrate specificity of the UDP-sulfoquinovose:diacylglycerol sulfoquinovosyltransferase that is encoded by sqdD and that catalyzes the final reaction of sulfolipid biosynthesis.

Stereochemistry of the acyl dihydroxyacetone phosphate acyl exchange reaction.

The fatty acid of acyl dihydroxyacetone phosphate can be exchanged enzymatically for another fatty acid. It has been shown that this reaction proceeds by cleavage of the oxygen bound to C-1 of the dihydroxyacetone phosphate (DHAP) moiety rather than by the more common cleavage at the acyl to oxygen bond. In the present study, the stereochemistry of this reaction was defined further; using deuterated substrates and fast atom bombardment-mass spectrometry, it was shown that the fatty acid exchange involves the stereospecific labilization of the pro-R hydrogen at C-1 of the DHAP moiety of acyl DHAP. The mechanism of ether bond formation, in which acyl DHAP is converted to O-alkyl DHAP, also proceeds via labilization of the pro-R hydrogen and cleavage of the fatty acid at the C-1 to oxygen bond. In addition, other workers have provided evidence that the enzyme responsible for the exchange reaction is O-alkyl DHAP synthetase. Therefore, the present results support the hypothesis that the acyl exchange is the reverse reaction of the first step in O-alkyl DHAP synthesis; in both of these reactions the pro-R hydrogen of C-1 of the DHAP moiety of acyl DHAP and the fatty acid moiety are labilized with cleavage of the fatty acid at the DHAP C-1 to oxygen bond.

Synthesis of regiospecifically labeled [18O]glycolic acid and [18O]acyldihydroxyacetone phosphate.

Methods are detailed for the preparation of [2-18O]glycolate from chloroacetic acid and for the direct conversion of these intermediates to regiospecifically labeled [2-18O]-2-O-acylglycolic acids containing approximately 90% 18O at the C-O-acyl bond. Methods are also detailed for optimization of reaction conditions and yields for each synthetic step in previously published methods for the preparation of 1-O-acyldihydroxyacetone-3-O-phosphate (DHAP) from acyloxyacetic acid (i.e., 2-O-acylglycolic acid), where acyl is tetradecanoyl, hexadecanoyl, or heptadecanoyl. The optimized reaction conditions generate 1-O-acyl DHAP in its acid form, both in high overall yield and in high purity, without requiring a final chromatographic purification of the product, 1-O-acyl DHAP. Combining these new methods, efficient and facile preparations of regiospecifically labeled [1-18O]-1-O-hexadecanoyl DHAP and [1-18O]-1-O-heptadecanoyl DHAP have now been demonstrated, in which approximately 90% 18O is specifically located only at the C-O-acyl position. Some mechanistic postulates are offered to account for the optimized yields, regioselectivities, and high 18O incorporation which are observed in the reactions we have employed to generate 1-O-acyl DHAP from glycolate intermediates.

O-alkyl lipid synthesis: the mechanism of the acyl dihydroxyacetone phosphate fatty acid exchange reaction.

We have previously provided evidence for a mechanism by which acyl DHAP is converted enzymatically to O-alkyl DHAP. This mechanism involves, in part, the formation of an endiol of acyl DHAP, loss of the fatty acid by splitting of the DHAP carbon-1 to oxygen bond and the gain of a long chain fatty alcohol. It has been shown that acyl DHAP can exchange its fatty acid for one in the medium, presumably by the mediation of O-alkyl DHAP synthase. In the present investigation we have shown that the fatty acid which is gained by acyl DHAP in the exchange process retains both carboxyl oxygens, as predicted by our postulated mechanism. This reaction is exceptional because the usual action of acyl hydrolases is to cleave at the oxygen to acyl bond.

Protection of photosensitized rats against long ultraviolet radiation by topical application of compounds with structures similar to that of dihydroxyacetone.

Dihydroxyacetone (DHA), a browning agent, protects photosensitive rats and humans against long ultraviolet radiation (UVA, 320-400 nm) and visible (blue) light. The photoprotective efficacy of DHA and structurally similar compounds was assessed as prevention of edema in the paws of psoralen-sensitized rats, after exposure to blacklight fluorescent lamps. Methylglyoxal produced a yellow-brown color and provided nearly the same protection as DHA, whereas monohydroxyacetone did not color the skin and afforded little or no protection. Glyceraldehyde provided a moderate amount of protection, which was enhanced by prior exposure of the agent to alkaline pH. A solution of 5-hydroxymethylfurfuraldehyde was yellow and provided minimal protection by staining the skin rather than browning it. We conclude that the ability to produce a brown color in skin is a useful criterion for screening compounds for photoprotective efficacy against UVA radiation.

Metabolism of alpha-glyceryl ethers by Crithidia fasciculata. I. Study of the in vivo degradation of exogenous chimyl and batyl alcohols.

[14C] chimyl and [3H] batyl alcohols were added to Crithidia fasciculata cultures during the mid-log phase of cell growth, and the lipid extracts of the cells were analyzed for degradation products. C. fasciculata cells were able to take up exogenous glyceryl ethers, and in amounts as high as the endogenous lipid content. The glyceryl ether taken up by the cells was incorporated into lipids either prior to the ether bond cleavage or after degradation to fatty acid. The extent of degradation and the degree of incorporation of degradation products into cellular lipid were higher for chimyl than for batyl alcohol. Batyl alcohol was not metabolized efficiently, leading to the formation of large intracellular pools of free substrate. One product of glyceryl ether degradation was identified as alkyl-dihydroxy acetone, and was detected inside and outside of the cells. The data strongly suggest that this product is the first stable intermediate in the degradation process and indicate that the extracellular formation of alkyl-dihydroxy acetone is due to the action of exoenzymes secreted by the cells. The constant detection of alk-l-enyl glycerol among the degradation products indicates the existence of a second mechanism in C. fasciculata for converting the alkyl-to alkenyl-glycerol.