Yasumasa Miyazaki

An arginyl residue in rice UDP-arabinopyranose mutase is required for catalytic activity and autoglycosylation

Plants use UDP-arabinofuranose (UDP-Araf) to donate Araf residues in the biosynthesis of Araf-containing complex carbohydrates. UDP-Araf itself is formed from UDP-arabinopyranose (UDP-Arap) by UDP-arabinopyranose mutase (UAM). However, the mechanism by which this enzyme catalyzes the interconversion of UDP-Arap and UDP-Araf has not been determined. To gain insight into this reaction, functionally recombinant rUAMs were reacted with UDP-Glc or UDP-Araf. The glycosylated recombinant UAMs were fragmented with trypsin, and the glycopeptides formed were then identified and sequenced by LC-MS/MS. The results of these experiments, together with site-directed mutagenesis studies, suggest that in functional UAMs an arginyl residue is reversibly glycosylated with a single glycosyl residue, and that this residue is required for mutase activity. We also provide evidence that a DXD motif is required for catalytic activity.

Down-regulation of UDP-arabinopyranose mutase reduces the proportion of arabinofuranose present in rice cell walls.

Arabinoxylans may account for up to 25% of the mass of grass cell walls. The interactions of these polysaccharides with themselves and with cellulose and lignin is believed to affect the walls physical properties and increase the walls resistance to biochemical conversion to fermentable sugars. Arabinoxylans have a backbone composed of 1,4-linked β-D-xylosyl residues, some of which are substituted at O-2 or O-3 with single arabinofuranosyl (Araf) residues. The Araf residues are likely transferred from UDP-Araf to the xylan backbone by arabinofuranosyltransferases. UDP-Araf is itself formed from UDP-arabinopyranose (UDP-Arap) by UDP-arabinopyranose mutase (UAM). In this study, RNA interference (RNAi) was used to suppress UAM expression in rice plants and thereby reduce the amounts of UDP-Araf available for cell wall synthesis. Several of the transgenic plants had reduced proportions of Araf in their walls together with a decrease in the extent of substitution of the xylan backbone, and a reduction of between 25% and 80% in ferulic acid and p-coumaric acid contents of the cell walls. Those transgenic plants with >25% reduction in the amounts of Araf were dwarfed and infertile.

Identification of a CAP (adenylyl-cyclase-associated protein) homologous gene in Lentinus edodes and its functional complementation of yeast CAP mutants

The adenylyl-cyclase-associated protein, CAP, was originally identified in yeasts as a protein that functions in both signal transduction and cytoskeletal organization. This paper reports the identification of a cDNA and genomic DNA that encodes a CAP homologue from the mushroom Lentinus edodes. The L. edodes cap gene contains eight introns and an ORF encoding a 518 amino acid protein. The L. edodes CAP is 35.5% and 40.9% identical at the amino acid level with Saccharomyces cerevisiae CAP and Schizosaccharomyces pombe CAP, respectively. The C-terminal domain shows greater homology (39-46% identity) with yeast CAPs than does the N-terminal domain (27-35% identity). Southern blotting and Northern blotting results suggest that L. edodes cap is a single-copy gene and uniformly expressed. Expression of the L. edodes CAP in both Schiz. pombe and Sacch. cerevisiae complemented defects associated with the loss of the C-terminal domain function of the endogenous CAP. By using a yeast two-hybrid assay, an interaction was demonstrated between the L. edodes CAP and Schiz. pombe actin. This result and the functional complementation test indicate that CAP from L. edodes has a conserved C-terminal domain function.

Purification and Biochemical Characterization of Recombinant Rice UDP-Arabinopyranose Mutase Generated in Insect Cells

Plants utilize UDP-arabinofuranose (UDP-Araf) in the biosynthesis of Araf-containing complex carbohydrates. UDP-Araf is synthesized from UDP-arabinopyranose by UDP-arabinopyranose mutases (UAMs). Here we describe the heterologous expression of rice (Oryza sativa) UAM genes in insect cells and report some of their enzymatic properties. Recombinant UAMs might serve as useful tools for the biosynthesis of UDP-Araf and might be better than chemical synthesis.

The fruiting-specific Le.flp1 gene, encoding a novel fungal fasciclin-like protein, of the basidiomycetous mushroom Lentinula edodes.

To understand the molecular mechanisms of fruiting body formation of basidiomycetous mushrooms, we have isolated over a 100 of developmentally regulated genes that were specifically transcribed during fruiting body development in Lentinula edodes (Shiitake-mushroom) by a subtractive hybridization, cDNA-RDA (cDNA representational difference analysis). One of these genes, named Le.flp1, was isolated from the primordial cDNA library of L. edodes, and the expression product of Le.flp1 and putative fungal homologues contained a characteristic region, homologous to the Fas domain of fasciclin family proteins, which are capable of promoting cell adhesion through Fas domain-mediated homophilic interactions in various organisms. RT-PCR analyses suggested that Le.flp1 was specifically expressed in primordia and mature fruiting bodies. In situ hybridization indicated that Le.flp1 transcripts were distributed distinctly in the following tissues: the inside of gills of fruiting bodies, especially at the boundary between the subhymenium and trama, where there is active proliferation of basidium cells for producing basidiospores; peripheral regions of the primordium, pileus and stipe; and both inner tissue and outer regions of the stipe. Our results suggest the hypothesis that Le.flp1 plays a role in cellular differentiation and development in ubiquitous tissues during fruiting body formation in L. edodes, possibly through cell adhesion.

Molecular cloning of the promoter region of the glyceraldehyde-3-phosphate dehydrogenase gene that contributes to the construction of a new transformation system in Coriolus versicolor

The white-rot basidiomycete Coriolus versicolor secretes several enzymes that participate in the degradation of lignin and various persistent organic pollutants. In this study, we attempted to establish a genetic transformation system with a homogenous promoter sequence for driving the gene for antibiotic resistance. We succeeded in cloning the promoter sequence of the gene for glyceraldehyde-3-phosphate dehydrogenase (gpd), which is expressed at high levels in C. versicolor. The expression vector pT7GPTHPT was constructed, which included a gene for resistance to hygromycin B under control of the gpd promoter. The successful selection of transformants on medium that contained hygromycin B indicated that the system should be useful not only for the genetic transformation of C. versicolor, but also for the overproduction of useful fungal enzymes such as laccase and peroxidase.

Distribution of Hydrophobin 1 Gene Transcript in Developing Fruiting Bodies of Lentinula edodes

Results of in situ RNA-RNA hybridization showed the presence of transcripts of the Lentinula edodes hydrophobin 1 gene, Le.hyd1, everywhere in the mycelial tissues of developing fruiting bodies except for the top parts of the pileus (cap) and for the prehymenophore. A high level of the transcript was detected in the parts surrounding the prehymenophore.

Stimulative effects of light and a temperature downshift on transcriptional expressions of developmentally regulated genes in the initial stages of fruiting-body formation of the basidiomycetous mushroom Lentinula edodes.

Quantitative reverse transcription PCR experiments were done to analyze the effects of light and a temperature downshift on transcriptional expressions of a variety of developmentally regulated genes in the initial stages of fruiting-body formation of Lentinula edodes wild-type strain FMC2. It was revealed that both proper light conditions and a temperature downshift are required for high levels of transcriptions of the genes and the formation of fruiting bodies. In L. edodes MIL-LEW-M13-1 strain, which has been reported previously to be capable of forming fruiting bodies without a low-temperature treatment, the expressions of the developmentally regulated genes were enhanced by light exposure.

Target genes of the developmental regulator PRIB of the mushroom Lentinula edodes

Using the method of genomic binding-site cloning, we identified three target genes of the developmental regulator, the product of priB gene (PRIB) in Lentinula edodes: the previously cloned priB and uck1 (UMP-CMP kinase gene) and a new gene, which we named mfbC. Identification of the former two genes was expected, because the promoter regions of priB and the gene encoding UMP-CMP kinase (uck1) have been shown to contain four or two consensus-like sequences of PRIB binding respectively. The mfbC gene contained two consensus-like sequences of PRIB binding in its promoter region and the PRIB protein bound them. The deduced 330 amino acid sequence of the product of mfbC gene (MFBC) was highly homologous to the 325 amino acid sequence of S. cerevisiae YJR070C/Lia1, the protein interacting with a putative translation initiation factor. Only the mature fruiting body of L. edodes was shown to contain the transcript of the mfbC gene almost exclusively, suggesting that mfbC may play a role in the final stage of fruiting-body formation.

Genetic Evidence That Two Types of Retroelements Evolved through Different Pathways in Ectomycorrhizal Homobasidiomycetes Tricholoma spp.

We designed a polymerase chain reaction that allows us to clone two types of putative reverse transcriptase genes from 11 species of ectomycorrhizal basidiomycetes that belong to the genus Tricholoma. One corresponds to the putative gene of marY1, a long terminal repeat (LTR) retroelement from Tricholoma matsutake, and the other, marY2N, a LINE-like non-LTR (L1-like) retroelement from this fungus. Putative protein products predicted from nucleotide sequencing of cloned fragments were phylogenetically analyzed. marY1-like elements had a parallel phylogenetic relationship with no apparent correlation to a current taxonomic profile, while marY2N-like elements showed a vertical one in relation to host-plant species. Data suggest that marY1-like elements and marY2N-like elements have evolved independently, and the evolution of marY1-like elements could have occurred later than the evolution of marY2N-like elements in the species of Tricholoma.