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Park Youngjin,Kim Yonggyun Korean Society of Applied Entomology 2005 Journal of Asia-Pacific Entomology Vol.8 No.1
It has been suggested that an entomopathogenic bacterium, Xenorhabdus nematophila, exerts its pathogenicity against beet armyworm, Spodoptera exigua, by inhibiting phospholipase $A_2\;(PLA_2)$ to shut down release of arachidonic acid, which is the primary substrate for eicosanoid biosynthetic pathway. This research aimed to prove the inhibitory hypothesis of X. nematophila on $PLA_2$ by directly quantifying arachidonic acid released from natural biological membrane. For determining optimal membrane preparation, fatty acid compositions from different tissues (hemocyte, fat body, and gut) were analyzed using gas chromatography in S. exigua. These tissue membranes showed different compositions in fatty acids, but possessed significant levels of arachidonic acid, amounting to ${\approx}\;0.02\%$ among all fatty acids. Also, all cytosolic fractions of three tissues possessed significant and specific $PLA_2$ activity because these $PLA_2$ extracts catalyzed release of arachidonic acid from the membrane preparation into medium and were inhibited by a specific $PLA_2$ inhibitor, dexamethasone. For massive assay, we chose fat body as a tissue source of $PLA_2$ and substrate membrane because of its relative abundance. The effect of fat body $PLA_2$ extract on release of arachidonic acid increased with its concentration and incubation time. The fat body $PLA_2$ was susceptible to dexamethasone (a specific $PLA_2$ inhibitor) and p-bromophenacyl bromide (a secretory type $PLA_2$ inhibitor), but not to methylarachidonyl fluorophosphate (a cellular type $PLA_2$ inhibitor). X nematophila significantly inhibited fat body $PLA_2$ activity, but did not after heat-killing. An organic extract of X. nematophila culture broth also inhibited the fat body $PLA_2$ activity. These results indicate that S. exigua possesses arachidonic acid on the membrane and $PLA_2$ in tissues and that X. nematophila releases $PLA_2$ inhibitor(s) and inhibits $PLA_2$, which is susceptible to a secretory type $PLA_2$ inhibitor.
Park Youngjin,Vatanparast Mohammad,Minoo Sajjadian Seyedeh 한국응용곤충학회 2022 Journal of Asia-Pacific Entomology Vol.25 No.2
The red imported fire ant (RIFA), Solenopsis invicta, is one of the globalized invasive pests. This study focused on pathogenicity and virulence of entomopathogenic fungi as one of the biological control agents to RIFA workers under different temperatures. The fungal pathogen, Beauveria bassiana ANU1 was isolated from Korea in 2015 and showed the pathogenicity to RIFA workers. A conidial suspension (1 × 10 7 conidia/ml) induced a low mortality from day 2 after treatment and reached to 100% mortality at day 7 and day 8 after treatment for major and minor workers, respectively. The median lethal concentrations of B. bassiana ANU1 were calculated as 3.9 × 10 3 for major and 4.6 × 10 3 for minor workers at day 7 after treatment. Low temperatures decreased a virulence of B. bassiana ANU1 (1 × 10 7 conidia/ml) to RIFA and showed mortality of 26.6% for major and 20% for minor workers. Based on bioassay results, this study provides one of possibilities of effective and successful strategy for controlling RIFA by entomopathogenic fungi.
Cadherin as a specific Cry1Ac receptor in the diamondback moth, Plutella xylostella
Youngjin Park,Yonggyun Kim 한국응용곤충학회 2013 한국응용곤충학회 학술대회논문집 Vol.2013 No.10
Putative cadherin genes, which are a receptor of the Bacillus thuringinesis toxins, were predicted from a whole genome sequencing data from the diamondback moth, Plutella xylostella. After the sequence and expression analysis, a Bt receptor cadherin gene was selected. The P. xylostella cadherin gene (PxCad1, GenBank Accession no. GU901158.1) encodes 11 cadherin repeats and a transmembrane domain. The PxCad1 gene was expressed in all developmental stage specifically in gut tissue by RT-PCR analysis. Expression of PxCad1 gene was suppressed by feeding of its specific dsRNA PxCad1 in 4th instar larval stage. The suppression of PxCad1 expression did not significantly feeding of its specific dsRNA PxCad1 in 4th instar larval stage. The suppression of PxCad1 expression did not significantly influence on pupal and adult development of P. xylostella. However, the larval treated with dsRNA PeCad1 (150 ng/larva) significantly reduced susceptibility to B. thuringiensis Cry1Ac (4.83 μg/ml). By contrast, the dsRNA PxCad1 -treated larvae did not show any change in susceptibility to B. thuringiensis Cry1Ca (0.24 μg/ml). These results suggest that PxCad1 is a specific receptor of Cry1Ac toxin from B. thuringiensis in P. xylostella.
High-modulus and strength carbon nanotube fibers using molecular cross-linking
Park, Ok-Kyung,Choi, Hoikil,Jeong, Hanbin,Jung, Yeonsu,Yu, Jaesang,Lee, Jae Kwan,Hwang, Jun Yeon,Kim, Seung Min,Jeong, Youngjin,Park, Chong Rae,Endo, Morinobu,Ku, Bon-Cheol Elsevier 2017 Carbon Vol.118 No.-
<P>We present a systematic and simple approach to produce high-strength carbon nanotube fibers (CNTFs) with electrical conductivity in the high performance range (> 1000 S/cm). We studied several critical parameters to improve the mechanical properties of CNTFs by aryl cross-linking reaction. Both the molecular dynamics (MD) simulations and experimental results showed that the mechanical properties strongly depended on the degree of cross-linking, length of cross-linkers, and CNT diameter. The monobenzene (MB) covalent bonding between CNTF with double-walled CNTs (DWCNTs) showed the highest load transfer, resulting in significantly enhanced specific tensile strength (3.7 N/tex) and Young's modulus (210 N/tex) which are superior to the strongest commercial carbon fiber (3.6 N/tex and 180 N/tex), respectively. Furthermore, the mechanical properties of aryl cross-linked CNTF exhibited no significant change in strength with sample size of CNTFs, showing uniformity of strength with increasing degree of cross-linking. The electrical conductivity of the MB cross-linked CNTFs was similar to 1400 S/cm, which is higher than the best value of commercial carbon fibers (715 S/cm). These results demonstrate that aromatic linker between CNTFs can significantly enhance mechanical properties without significant loss of electrical conductivity. These molecular engineering with MD simulations provide an important route to design and develop ultra-high-performance fibers. (C) 2017 Elsevier Ltd. All rights reserved.</P>
Youngjin Park,Yonggyun Kim 한국응용곤충학회 2013 한국응용곤충학회 학술대회논문집 Vol.2013 No.04
The beet armyworm, Spodoptera exigua, is a freeze-susceptible species and overwinters without diapause in temperate zone. Depression of supercooling point (SCP) and rapid cold hardiness (RCH) allow S. exigua to survive at low temperatures. This study reports a polyol which is responsible for the cold hardiness of S. exigua. Pre-exposure of S. exigua larvae to 4°C for 6 h significantly enhanced survival under a freezing temperature (-10°C). This pre-exposure treatment also significantly depressed larval SCPs. Analysis of polyols indicated that glycerol titers significantly increase with increase of pre-exposure time. Glycerol kinase (GK) and glycerol-3-phosphate dehydrogenase (GPDH) are involved in glycolysis pathway of insect. The S. exigua GK (SeGK1) and G3PDH (SeG3PDH1) genes were predicted from 454 pyrosequencing transcripts from fifth instar larvae of the beet armyworm, S. exigua. The SeGK1 and SeG3PDH1 genes both were expressed in all larval stage by RT-PCR analysis. Expression of SeGK1 and SeG3PDH1 genes were suppressed by its specific dsRNASeGK1 or dsRNASeG3PDH1 injection into hemocoel of 5th instar larva. Each 200 ng of dsRNASeGK1 or dsRNASeG3PDH1 injection also significantly decreased glycerol amount in hemolymph. Larval treated by either dsRNASeGK1 or dsRNASeG3PDH1 significantly lost the RCH under -10°C exposure. These results indicate that glycerol is a crucial RCH agent and its synthesis is regulated by SeGK1 and SeG3PDH1 genes in S. exigua.