Tae Kyung Hyun

Hovenia dulcis--an Asian traditional herb.

Hovenia dulcis Thunb., known as Japanese raisin tree, is commonly found in East Asia. It has a long history as a food supplement and traditional medicine in Japan, China and Korea, but is little known and used in Western countries so far. This minireview summarizes traditional uses and current knowledge on the pharmacology and phytochemistry of H. duclcis and covers, in particular, literature from specialized Asian journals that are not readily accessible. Extracts from H. dulcis accelerate detoxification of ethanol, and possess hepatoprotective, antioxidative, antimicrobial and antidiabetic properties. Although the underlying molecular mechanisms are not fully understood, free radical scavenging and enhancement of ethanol catabolism have been reported.

Metabolic control of tobacco pollination by sugars and invertases

Invertases and hexose transporters, as essential components of carbohydrate supply, are regulated in a spatiotemporally coordinated manner to maintain functionality of tobacco pollination. Pollination in flowering plants is initiated by germination of pollen grains on stigmas followed by fast growth of pollen tubes representing highly energy-consuming processes. The symplastic isolation of pollen grains and tubes requires import of Suc available in the apoplast. We show that the functional coupling of Suc cleavage by invertases and uptake of the released hexoses by monosaccharide transporters are critical for pollination in tobacco (Nicotiana tabacum). Transcript profiling, in situ hybridization, and immunolocalization of extracellular invertases and two monosaccharide transporters in vitro and in vivo support the functional coupling in supplying carbohydrates for pollen germination and tube growth evidenced by spatiotemporally coordinated expression. Detection of vacuolar invertases in maternal tissues by these approaches revealed metabolic cross talk between male and female tissues and supported the requirement for carbohydrate supply in transmitting tissue during pollination. Tissue-specific expression of an invertase inhibitor and addition of the chemical invertase inhibitor miglitol strongly reduced extracellular invertase activity and impaired pollen germination. Measurements of (competitive) uptake of labeled sugars identified two import pathways for exogenously available Suc into the germinating pollen operating in parallel: direct Suc uptake and via the hexoses after cleavage by extracellular invertase. Reduction of extracellular invertase activity in pollen decreases Suc uptake and severely compromises pollen germination. We further demonstrate that Glc as sole carbon source is sufficient for pollen germination, whereas Suc is supporting tube growth, revealing an important regulatory role of both the invertase substrate and products contributing to a potential metabolic and signaling-based multilayer regulation of pollination by carbohydrates.

Tomato mitogen activated protein kinases regulate the expression of extracellular invertase Lin6 in response to stress related stimuli

Activation of mitogen-activated protein kinases (MAPKs) is a common reaction of plant cells in defence-related signal transduction pathways. Since the downstream events after the activation of MAPKs are largely unknown in plants, the role of MAPKs in the coordinate regulation of defence reactions and primary carbon metabolism by stress related stimuli has been analysed in tomato (Lycopersicon peruvianum Mill.). Thus, the relationship between MAPK, LpMPK2 and LpMPK3 and extracellular invertase Lin6, as the key enzyme of an apoplasmic phloem unloading pathway, has been analysed. It was observed that the mRNAs of LpMPK3 and Lin6 are sequentially induced by the same set of stress related stimuli, wounding, a fungal elicitor derived from Fusarium oxysporum lycopersici, the endogenous plant derived elicitor PGA and salt stress, while LpMPK2 transcripts are constitutively expressed. In a gain of function approach, a His-tagged version of LpMPK2 and a HA-tagged version of LpMPK3 were transiently and functionally expressed in leaves of transgenic tobacco (Nicotiana tabacum L.) plants expressing the β-glucuronidase reporter gene under control of the Lin6 promoter via agro-infection. The induction of the Lin6 promoter, as revealed by an increase in β-glucuronidase activity after 24 h, was dependent both on the expression and activation of both LpMPK2 and LpMPK3. These data suggest that the induction of extracellular invertase Lin6 by stress-related stimuli requires LpMPK2 and LpMPK3, and thus demonstrate that MAPK signalling might be involved in the regulation of primary carbon metabolism in general and sink metabolism in particular.

The Arabidopsis PLAT domain protein1 is critically involved in abiotic stress tolerance.

Despite the completion of the Arabidopsis genome sequence, for only a relatively low percentage of the encoded proteins experimental evidence concerning their function is available. Plant proteins that harbour a single PLAT (Polycystin, Lipoxygenase, Alpha-toxin and Triacylglycerol lipase) domain and belong to the PLAT-plant-stress protein family are ubiquitously present in monocot and dicots. However, the function of PLAT-plant-stress proteins is still poorly understood. Therefore, we have assessed the function of the uncharacterised Arabidopsis PLAT-plant-stress family members through a combination of functional genetic and physiological approaches. PLAT1 overexpression conferred increased abiotic stress tolerance, including cold, drought and salt stress, while loss-of-function resulted in opposite effects on abiotic stress tolerance. Strikingly, PLAT1 promoted growth under non-stressed conditions. Abiotic stress treatments induced PLAT1 expression and caused expansion of its expression domain. The ABF/ABRE transcription factors, which are positive mediators of abscisic acid signalling, activate PLAT1 promoter activity in transactivation assays and directly bind to the ABRE elements located in this promoter in electrophoretic mobility shift assays. This suggests that PLAT1 represents a novel downstream target of the abscisic acid signalling pathway. Thus, we showed that PLAT1 critically functions as positive regulator of abiotic stress tolerance, but also is involved in regulating plant growth, and thereby assigned a function to this previously uncharacterised PLAT domain protein. The functional data obtained for PLAT1 support that PLAT-plant-stress proteins in general could be promising targets for improving abiotic stress tolerance without yield penalty.

De novo transcriptomic analysis to reveal functional genes involved in triterpenoid saponin biosynthesis in Oplopanax elatus NAKAI

Oplopanax elatus is a valuable medicinal plant in the family Araliaceae that recommends itself as source of herbal preparations. Although, as in ginseng, triterpenoid saponins make up the major bioactive component of O. elatus , nothing is known about the genes that are involved in the biosynthesis of these complex compounds, as reflected also by a lack of genomic information in public databases. Using Illumina paired-end sequencing technology, we have therefore generated a transcriptome library of O. elatus from a pooled RNA sample from different organs. 208,959 unigenes were assembled from approximately 77 million high-quality reads, and 110,202 unigenes (52.7% of the unigenes) were annotated. In addition, 47,273 cDNA-derived SSRs in 38,446 unigenes were identified as potential molecular markers. Furthermore, 122 unigenes encoding 47 putative enzymes related to the biosynthesis of the backbone of triterpenoid saponins were identified by analyzing our library. The organ-specific expression of selected genes suggests that the leaves of O. elatus are the main site of triterpenoid saponin biosynthesis. The transcriptome data reported here provides valuable and comprehensive information for further research into the metabolic pathways of O. elatus as well as into genetic variation in the Oplopanax genus. The online version of this article (doi: 10.5073/JABFQ.2017.090.004) contains supplementary files .

The Arabidopsis PLAT domain protein1 promotes abiotic stress tolerance and growth in tobacco

AbstractPlant growth and consequently crop yield can be severely compromised by abiotic and biotic stress conditions. Transgenic approaches that resulted in increased tolerance against abiotic stresses often were typically accompanied by adverse effects on plant growth and fitness under optimal growing conditions. Proteins that belong to the PLAT-plant-stress protein family harbour a single PLAT (Polycystin, Lipoxygenase, Alpha-toxin and Triacylglycerol lipase) domain and are ubiquitously present in monocot and dicot plant species. Until now, only limited data is available for PLAT-plant-stress family members, which suggested that these proteins in general could promote tolerance towards stress responses. We studied the function of the Arabidopsis PLAT-plant-stress protein AtPLAT1 employing heterologous gain-of-function analysis in tobacco. AtPLAT1 conferred increased abiotic stress tolerance in tobacco, evident by improved tolerance towards cold, drought and salt stresses, and promoted growth, reflected by a faster development under non-stressed conditions. However, the overexpression of AtPLAT1 in tobacco reduced the tolerance towards biotic stress conditions and, therefore, could be involved in regulating the crosstalk between abiotic and biotic stress responses. Thus, we showed that heterologously expressed AtPLAT1 functions as positive regulator of abiotic stress tolerance and plant growth, which could be an important new asset for strategies to develop plants with improved abiotic stress tolerance, without growth and subsequent yield penalties under optimal growth conditions.

Polyphenolic compounds, antioxidant and anti-inflammatory effects of Abeliophyllum distichum Nakai extract

The present study was conducted to evaluate the antioxidant and anti-inflammatory activities of crude methanolic extract of Abeliophyllum distichum Nakai, and those of its partitioned fractions, including hexane, ethyl acetate, n-butanol, and aqueous. The antioxidant activities were analyzed by DPPH free radical scavenging and oxygen radical antioxidant capacity assay. Results showed that the BuOH fraction possessed a strong antioxidant activity through a hydrogen atom transfer reaction-based mechanism and a single electron transfer reaction-based mechanism. In lipopolysaccharide (LPS)-stimulated RAW 264.7 cells, the BuOH fraction of A. distichum methanol extract exhibited a strong inhibitory effect on the nitric oxide production and inhibited the expression of pro-inflammatory mediators, including COX-2, TNF-α, and IL-6, through the inhibition of the MEK/ERK signaling pathway. In addition, the BuOH fraction inhibited the LPS-induced ROS level through the NADPH oxidase-independent mechanism. Furthermore, HPLC analysis identified chlorogenic acid, caffeic acid, gentisic acid, rutin, ferulic acid, and quercetin, and suggested that the antioxidant and anti-inflammatory activities of the BuOH fraction should be mediated by the presence of higher amounts of caffeic acid, rutin, and ferulic acid than other fractions. Taken together, these results suggest that A. distichum extract is a source of antioxidant and anti-inflammatory compounds, and could be developed as a potential source for functional food and dietary health supplement.

Molecular cloning and functional characterization of the flavonoid 3′-hydroxylase gene from Rubus coreanus Miquel

Rubus coreanus Miquel is a Korean black raspberry used in folk medicine and functional foods. To investigate the biosynthesis pathway of anthocyanin in R. coreanus Miquel, the complete coding sequence of flavonoid 3′-hydroxylase (F3′H), designated as RcMF3′H1, was cloned for the first time using the Korean black raspberry transcriptome library. The deduced amino acid sequence of RcMF3′H1 contained the proline-rich “hinge” region, P450 consensus heme-binding domain, and F3′H-specific motifs. Phylogenetic analysis revealed that RcMF3′H1 was clustered into the same subgroup as other plant F3′Hs. In addition, expression analysis by quantitative real-time PCR revealed the involvement of RcMF3′H1 in methyl jasmonate-mediated anthocyanin biosynthesis. Furthermore, the ability of the RcMF3′H1 gene to complement the Arabidopsis transparent testa 7-1 mutant suggested that RcMF3′H1 encodes the functional F3′H enzyme involved in anthocyanin biosynthesis. Taken together, the cloning and molecular characterization of RcMF3′H1 will facilitate a better insight into the anthocyanin biosynthesis pathway in R. coreanus Miquel.

Proteomic analysis of mycelial proteins from Rosellinia necatrix

The soilborne pathogen Rosellinia necatrix causes white root rot, a serious disease of various trees, and is extremely difficult to control. In this study, using one-dimensional electrophoresis coupled with nanoliquid chromatography-electrospray ionization quadrupole time-of-flight tandem mass spectrometry (ESI-Q-TOF-MS/MS), we identified 696 proteins from R. necatrix mycelium (KACC 40445) grown in liquid culture. In addition, 573 proteins were assigned to at least one gene ontology term including 26 functional groups. Most were related to catalytic activity in the molecular function category. This proteomic data set advances understanding of R. necatrix biology and will inform further investigations to manage white root rot using novel strategies.

Identification and expression profiling of flax (Linum usitatissimum L.) polyamine oxidase genes in response to stimuli

Abstract Polyamine oxidases (PAOs) are known to be involved in either the terminal catabolism or the back conversion of polyamines, which affect a range of physiological processes, including growth, development, and stress responses. In this study, based on genome-wide analysis, we identified five putative PAO genes (LuPAO1 to LuPAO5) in flax (Linum usitatissimum L.) that contain the amino-oxidase domain and FAD-binding-domain. The expression analysis using quantitative real-time PCR revealed spatial variations in the expression of LuPAOs in different organs. In addition, the expression level of LuPAOs in the flax cell suspension culture was increased by treatment with methyl-jasmonate (MeJA) or pectin, but not with salicylic acid or chitosan. This indicates that LuPAOs might be involved in the MeJA-mediated biological activities. Taken together, our genome-wide analysis of PAO genes and expression profiling of these genes provide the first step toward the functional dissection of LuPAOs.