Receptor-like protein kinase 2 (RPK 2) is a novel factor controlling anther development in Arabidopsis thaliana

Receptor-like kinases (RLK) comprise a large gene family within the Arabidopsis genome and play important roles in plant growth and development as well as in hormone and stress responses. Here we report that a leucine-rich repeat receptor-like kinase (LRR-RLK), RECEPTOR-LIKE PROTEIN KINASE2 (RPK2), is a key regulator of anther development in Arabidopsis. Two RPK2 T-DNA insertional mutants (rpk2-1 and rpk2-2) displayed enhanced shoot growth and male sterility due to defects in anther dehiscence and pollen maturation. The rpk2 anthers only developed three cell layers surrounding the male gametophyte: the middle layer was not differentiated from inner secondary parietal cells. Pollen mother cells in rpk2 anthers could undergo meiosis, but subsequent differentiation of microspores was inhibited by tapetum hypertrophy, with most resulting pollen grains exhibiting highly aggregated morphologies. The presence of tetrads and microspores in individual anthers was observed during microspore formation, indicating that the developmental homeostasis of rpk2 anther locules was disrupted. Anther locules were finally crushed without stomium breakage, a phenomenon that was possibly caused by inadequate thickening and lignification of the endothecium. Microarray analyses revealed that many genes encoding metabolic enzymes, including those involved in cell wall metabolism and lignin biosynthesis, were downregulated throughout anther development in rpk2 mutants. RPK2 mRNA was abundant in the tapetum of wild-type anthers during microspore maturation. These results suggest that RPK2 controls tapetal cell fate by triggering subsequent tapetum degradation, and that mutating RPK2 impairs normal pollen maturation and anther dehiscence due to disruption of key metabolic pathways.     

Biodiesel production using anionic ion-exchange resin as heterogeneous catalyst

The transesterification reactions of triolein with ethanol using various ion-exchange resin catalysts were conducted to produce ethyl oleate as a biodiesel. The anion-exchange resins exhibited much higher catalytic activities than the cation-exchange resin. The anion-exchange resin with a lower cross-linking density and a smaller particle size gave a high reaction rate as well as a high conversion. By combining the three-step regeneration method, the resin could be repeatedly used for the batch transesterification without any loss in the catalytic activity. A continuous transesterification reaction was carried out using an expanded bed reactor packed with the most active resin. The reactor system permitted the continuous production of ethyl oleate with a high conversion.     

Antibacterial activity of a virgatusin-related compound

The relationship between antibacterial activity of tetra-substituted tetrahydrofuran lignans (1-4) and their absolute configurations was tested. Only compound 4 among two virgatusins and two related compounds exhibited growth inhibitory activity against the Gram-positive bacteria Bacillus subtilis, Staphylococcus aureus and Listeria denitrificans. Compound 4 affected the growth of B. subtilis in a bactericidic manner, and its ability to dissipate the cytoplasmic membrane potential was investigated using the fluorescence probe 3,3'-dipropylthiadicarbocyanine iodide. These results suggested that compound 4 damages cells by causing the loss of the proton motive force and disruption of the cellular integrity of the membrane, leading to cell death. In addition, it was shown that the antibacterial activity of a lignan was closely related to its absolute configuration and functional groups.     

Synthesis of (+/-)-sundiversifolide based on Lewis acid-mediated Claisen rearrangement

A new and concise synthesis of (+/-)-sundiversifolide (1), an allelopathic bisnor-sesquiterpene lactone isolated from germinating sunflower (Helianthus annuus L.) seeds, was achieved by employing Lewis acid-mediated Claisen rearrangement as the key step.     

Molecular cloning and functional expression of soybean allene oxide synthases

A plant allene oxide synthase (AOS) reacting with 13S-hydroperoxy-9Z,11E,15Z-octadecatrienoic acid (13-HPOT), a lipoxygenase product of alpha-linolenic acid, provides an allene oxide which functions as an intermediate for jasmonic acid (JA) synthesis, making AOS a key enzyme regulating the JA level in plants. Although AOSs in various plants have been investigated, there is only limited information about AOSs in soybean (Glycine max). In this study, we cloned and characterized two soybean AOSs, GmAOS1 and GmAOS2, sharing 95% homology in the predicted amino acid sequences. GmAOS1 and GmAOS2 were composed of 564 and 559 amino acids respectively, with predicted N-terminal chloroplast-targeting signal peptides. Both AOSs expressed in Escherichia coli were selective for 13S-hydroperoxides of alpha-linolenic and linoleic acids, suggesting the potential of GmAOS1 and GmAOS2 to contribute to JA synthesis. GmAOS1 and GmAOS2 were expressed in leaves, stems, and roots, suggesting broad distribution in a soybean plant.     

Functional similarities of a thermostable protein-disulfide oxidoreductase identified in the archaeon <Emphasis Type="Italic">Pyrococcus horikoshii</Emphasis> to bacterial DsbA enzymes

We have isolated and characterized a gene for a putative protein-disulfide oxidoreductase (phdsb) in the archaeon Pyrococcus horikoshii. The open reading frame of phdsb encodes a protein of 170 amino acids with an NH₂-terminal extension similar to the bacterial signal peptides. The putative mature region of PhDsb includes a sequence motif, Cys-Pro-His-Cys (CPHC), that is conserved in members of the bacterial DsbA family, but otherwise the archaeal and bacterial sequences do not show substantial similarity. A recombinant protein corresponding to the predicted mature form of PhDsb behaved as a monomer and manifested oxidoreductase activities in vitro similar to those of DsbA of Escherichia coli. The catalytic activity of PhDsb was thermostable and was shown by mutation analysis to depend on the NH₂-terminal cysteine residue of the CPHC motif. Thus, in spite of their low overall sequence similarities, DsbA-like proteins of archaea and bacteria appear to be highly similar in terms of function.