Yong Hwa Cheong

A new reducing polyketide synthase gene from the lichen-forming fungus Cladonia metacorallifera

Lichens produce unique polyketide secondary metabolites including depsides, depsidones, dibenzofurans and depsones. The biosynthesis of these compounds is governed by polyketide synthase (PKS), but the mechanism via which they are produced has remained unclear until now. We reported the 6-methylsalicylic acid synthase (6-MSAS) type of PKS gene, which is a member of the fungal-reducing PKSs. A cultured mycobiont of Cladonia metacorallifera was employed in the isolation and characterization of a polyketide synthase gene (CmPKS1). The complete sequence information for CmPKS1 was acquired via the screening of a Fosmid genomic library with a 456 bp fragment corresponding to part of the acyl transferase (AT) domain as a probe. CmPKS1 contains β-ketoacyl synthase (KS), AT, dehydratase (DH), ketoreductase (KR) and phosphopantetheine attachment site (PP) domains.: The domain organization of CmPKS1 (KS-AT-DH-KR-PP) is a typical 6-MSAS-type PKS, and the results of phylogenetic analysis showed that CmPKS1 grouped with other fungal-reducing PKSs. Quantitative real time PCR analyses showed that CmPKS1 was expressed preferentially in the early growth stage of the axenically cultured mycobiont. Furthermore CmPKS1 expression was found to be dependent on the carbon sources and concentrations in the medium.

Diversity of endophytic fungi associated with bryophyte in the maritime Antarctic (King George Island)

Abstract Bryophytes comprise one of the richest microfungal microhabitats in the Antarctic environment. The maritime Antarctic is very vulnerable to rapid environmental change caused by global warming. The aim of this study was to investigate the importance of bryophytes as a microhabitat for fungal species in the maritime Antarctic by surveying endophytic fungal diversity from several bryophytes including Andreaea sp., Barbilophozia hatcheri, Chorisodontium aciphyllum, Polytrichum alpinum, Polytrichumstrictum, Sanionia uncinata, and Warnstorfia sarmentosa. We collected 13 bryophyte samples at four localities on Barton Peninsula, King George Island. In total, 31 endophytic fungi morphotypes were isolated from bryophyte tissues by a thorough surface sterilization method. Using internal transcribed spacer sequence analysis, 16 endophytic fungal strains belonging to Ascomycota (12), Basidiomycota (1), Oomycota (1), and Zygomycota (2) phyla were obtained. Our results suggest the presence of a diverse range of fungal species even in a very limited area, and those bryophytes play an important role in conserving fungal diversity in this harsh environment. Growth rate measurements at a wide range of temperatures confirmed that most of the fungal strains were both mesophilic and psychrotolerant. This is the first report of endophytic fungi in Antarctic moss tissue by fluorescence in situ hybridization.

Three New Non-reducing Polyketide Synthase Genes from the Lichen-Forming Fungus Usnea longissima

Abstract Usnea longissima has a long history of use as a traditional medicine. Several bioactive compounds, primarily belonging to the polyketide family, have been isolated from U. longissima. However, the genes for the biosynthesis of these compounds are yet to be identified. In the present study, three different types of non-reducing polyketide synthases (UlPKS2, UlPKS4, and UlPKS6) were identified from a cultured lichen-forming fungus of U. longissima. Phylogenetic analysis of product template domains showed that UlPKS2 and UlPKS4 belong to group IV, which includes the non-reducing polyketide synthases with an methyltransferase (MeT) domain that are involved in methylorcinol-based compound synthesis; UlPKS6 was found to belong to group I, which includes the non-reducing polyketide synthases that synthesize single aromatic ring polyketides, such as orsellinic acid. Reverse transcriptase-PCR analysis demonstrated that UlPKS2 and UlPKS4 were upregulated by sucrose; UlPKS6 was downregulated by asparagine, glycine, and alanine.

Isolation and characterization of a reducing polyketide synthase gene from the lichen-forming fungus Usnea longissima

The reducing polyketide synthases found in filamentous fungi are involved in the biosynthesis of many drugs and toxins. Lichens produce bioactive polyketides, but the roles of reducing polyketide synthases in lichens remain to be clearly elucidated. In this study, a reducing polyketide synthase gene (U1PKS3) was isolated and characterized from a cultured mycobiont of Usnea longissima. Complete sequence information regarding U1PKS3 (6,519 bp) was obtained by screening a fosmid genomic library. A U1PKS3 sequence analysis suggested that it contains features of a reducing fungal type I polyketide synthase with β-ketoacyl synthase (KS), acyltransferase (AT), dehydratase (DH), enoyl reductase (ER), ketoacyl reducatse (KR), and acyl carrier protein (ACP) domains. This domain structure was similar to the structure of ccRadsl, which is known to be involved in resorcylic acid lactone biosynthesis in Chaetomium chiversii. The results of phylogenetic analysis located U1PKS3 in the clade of reducing polyketide synthases. RT-PCR analysis results demonstrated that UIPKS3 had six intervening introns and that UIPKS3 expression was upregulated by glucose, sorbitol, inositol, and mannitol.

Characterization of two novel non-reducing polyketide synthase genes from the lichen-forming fungus Hypogymnia physodes

Lichens are known to produce a variety of secondary metabolites including polyketides, which have valuable biological activities. Some polyketides are produced solely by lichens. The biosynthesis of these compounds is primarily governed by iterative type I polyketide synthases. Hypogymnia physodes synthesize polyketides such as physodic, physodalic and hydroxyphysodic acid and atranorin, which are non-reducing polyketides. Two novel non-reducing polyketide synthase (PKS) genes were isolated from a fosmid genomic library of a mycobiont of H. physodes using a 409bp fragment corresponding to part of the reductase (R) domain as a probe. H. physodes PKS1 (Hyopks1) and PKS2 (Hypopks2) contain keto synthase (KS), acyl transferase (AT), acyl carrier protein (ACP), methyl transferase (ME) and R domains. Classification based on phylogeny analysis using the translated KS and AT domains demonstrated that Hypopks1 and Hypopks2 are members of the fungal non-reducing PKSs clade III. This is the first report of non-reducing PKSs containing the R domain-mediated release mechanisms in lichens, which are also rare fungal type I PKS in non-lichenized filamentous fungi.

Effects of Selenium Supplement on Germination, Sprout Growth and Selenium Uptake in Four Vegetables

This study was carried out to investigate the effect of selenium treatment on the growth of vegetables sprout. Four vegetables, such as cabbage, lettuce, pak-choi and leaf mustard were examined under various selenium treatments (0, 1, 5, 10, 25, 50, 100 mg L -1 ). Seed germinations in cabbage, pak-choi and leaf mustard were significantly inhibited at high concentration of selenium treatment. However, seed germination in lettuce was not much inhibited. Growth characteristics, such as soot length, root length, fresh weight and chlorophyll contents, were not much decreased at 1 mg L -1 of selenium and then significantly inhibited with the increase of selenium concentration at above 5 mg L -1 in all four vegetables. The selenium content increased linearly with the increase of selenium concentration. At the range of 1 to 25 mg L -1 of selenium treatment, selenium contents in vegetables were 0.11 to 1.15 of cabbage, 0.16 to 0.61 of lettuce, 0.13 to 1.31 of pak-choi and 0.14 to 1.13 mg g -1 dw of leaf mustard, respectively. These results showed that treatment of selenium with the range of 1 to 5 mg L -1 could be used to produce the selenium enriched vegetable sprouts.

Accumulation and Toxicity of Germanium in Cucumber under Different Types of Germaniums

The effects of germanium dioxide (GeO2) and 2-carboxyethyl germanium sesquioxide (Ge-132) treatments on cucumber (Cucumis sativus L.) growth and Ge accumulation and toxicity were investigated. Accumulated Ge contents in plant treated with GeO2 were two times greater than that in plants treated with Ge-132. Germanium accumulated primarily in the shoots in the GeO2 treatments and in the roots in the Ge-132 treatments. In contrast GeO2 was easily transported from roots to shoots. In cucumber fruit, the range of Ge content in both the GeO2 and Ge-132 treatments was in the order of stalk > rind > pulp > seeds, suggesting that Ge accumulation was based on distance from xylem. Silicon (Si) content significantly decreased as GeO2 concentration increased, but there was no difference in Si content in the Ge-132 treatment. Therefore, plant growth and Ge accumulation are affected differently by GeO2 and Ge-132 treatments, based partly on treatment concentrations.

Effects of Different Humic Acids on Growth and Fruit Quality of Tomato Plant

In greenhouse farming, a variety of humic acids have been applied to improve soil conditions and plant growth. However, it is still unclear that how humic acids combined with chemical fertilizers affect growth and quality of fruit vegetable crops. This study was conducted to determine the combination effect of humic acids and chemical fertilizers on the growth and fruit quality of tomato (Lycopersicon esculentum MILL.) grown under greenhouse conditions. Three different formulation types of humic acid were used: liquid type A, liquid type B and solid type C. The tomato plants were grown in three treatment combination plots and in conventional fertilizer (CF) plot with recommended levels of nitrogen, phosphorus and potassium: HA combined with CF (HA+CF), HB combined with CF (HB+CF) and HC combined with CF (HC+CF). For most of growth characteristics (i.e. leaf number, internode length, maximum leaf length, leaf width and chlorophyll contents) determined in this experiment, no significant differences were observed between all combination treatments and CF. However, integrated fruit qualities (i.e. averaged weight, sugar contents and acidity) were slightly improved in the humic acid combined with CF treatments when compared with CF alone treatment. No phytotoxicity was observed with humic acid treatments. However, further studies will probably be needed to use widely and safely these humic acids, in order to ensure a maximizing growth, fruit yield and quality of tomato.