Yong Hoon Lee

Light quality influences the virulence and physiological responses of Colletotrichum acutatum causing anthracnose in pepper plants.

To explore the effects of light quality on the physiology and pathogenicity of Colletotrichum acutatum, we analysed the morphological traits, melanin production and virulence of the pathogen under different light wavelengths.

Influence of light qualities on antifungal lipopeptide synthesis in Bacillus amyloliquefaciens JBC36

Bacillus amyloliquefaciens JBC36 (JBC36) is a potent biocontrol agent and was proved to control green and blue molds of Satsuma mandarin (Citrus unshiu). Moreover, light qualities affected its biocontrol efficacy; green and red light significantly increased the antifungal activity of the antagonist in our previous study. The disparity in antagonism on Penicillium digitatum under different light qualities prompted us to investigate further to identify the factors responsible for the noted variation. Purification and quantification of antifungal lipopeptides by HPLC revealed that a three-fold higher quantity of fengycin and a two-fold higher quantity of iturin were produced in cultures incubated with red and green light sources in comparison with white light illumination. Gene expression analysis by real-time PCR also revealed nearly fourfold higher fenA transcripts in cultures subjected to green and red light in comparison with white light illumination. The lowest gene expression was observed with blue light illumination. This study clearly proved that light affects the synthesis of antifungal lipopeptides in JBC36. A light-based lipopeptide production strategy may lead to better exploitation of the microbes for overproduction of the antifungal secondary metabolites and crop disease management.

Visual Analysis for Detection and Quantification of Pseudomonas cichorii Disease Severity in Tomato Plants

Pathogen infection in plants induces complex responses ranging from gene expression to metabolic processes in infected plants. In spite of many studies on biotic stress-related changes in host plants, little is known about the metabolic and phenotypic responses of the host plants to Pseudomonas cichorii infection based on image-based analysis. To investigate alterations in tomato plants according to disease severity, we inoculated plants with different cell densities of P. cichorii using dipping and syringe infiltration methods. High-dose inocula (≥ 106 cfu/ml) induced evident necrotic lesions within one day that corresponded to bacterial growth in the infected tissues. Among the chlorophyll fluorescence parameters analyzed, changes in quantum yield of PSII (ΦPSII) and non-photochemical quenching (NPQ) preceded the appearance of visible symptoms, but maximum quantum efficiency of PSII (Fv/Fm) was altered well after symptom development. Visible/near infrared and chlorophyll fluorescence hyperspectral images detected changes before symptom appearance at low-density inoculation. The results of this study indicate that the P. cichorii infection severity can be detected by chlorophyll fluorescence assay and hyperspectral images prior to the onset of visible symptoms, indicating the feasibility of early detection of diseases. However, to detect disease development by hyperspectral imaging, more detailed protocols and analyses are necessary. Taken together, change in chlorophyll fluorescence is a good parameter for early detection of P. cichorii infection in tomato plants. In addition, image-based visualization of infection severity before visual damage appearance will contribute to effective management of plant diseases.

Elucidation of the functional role of flagella in virulence and ecological traits of Pseudomonas cichorii using flagella absence (ΔfliJ) and deficiency (ΔfliI) mutants.

Understanding the infection mechanisms of pathogens will lead to better management of the associated diseases. The flagella of these pathogens play significant roles not only in bacterial motility, but also in virulence. In the present study, two genes involved in flagella construction, fliJ and fliI of Pseudomonas cichorii, were analyzed. The results revealed that these genes are vital for flagella formation and play significant roles not only in motility, but also in virulence. When we inoculated host plants with fliI- and fliJ-defective mutants (ΔfliJ and ΔfliI) through the dipping method, the degree of disease severity caused by both mutants was significantly reduced compared to those of the wild-type. However, the virulence of ΔfliI was stronger than that of ΔfliJ. Electron microscope observation, and swarming and leaf attachment assays indicated a reduced number of flagella in ΔfliI, but not complete absence, because of the presence of another copy of fliI. Furthermore, a vacuum infiltration assay revealed that flagella are indispensable in the pre- and post-penetration stages for complete virulence. Overall, we created semi-defective (ΔfliI) and completely defective (ΔfliJ) mutants and elucidated the fact that flagella play significant roles in virulence of the pathogen at different stages of the infection process.

Effects of green light on the gene expression and virulence of the plant pathogen Pseudomonas cichorii JBC1

Increasing evidence suggests that the interactions between plant and pathogen are influenced by light perception of both organisms. In our previous study, green light decreased disease severity in tomato plants in response to Pseudomonas cichoriiJBC1 (PcJBC1) infection via induction of disease resistance-related genes. However, the influence of green light on gene expression and metabolism of PcJBC1 has not been explored. In this study, we cultured PcJBC1 in hrp-inducing minimal media (MM) under green light and dark condition, and analyzed the expression of genes, which are important in pathogenicity/virulence and epiphytic survival by real-time PCR (qPCR). Although no significant changes were observed in the expression of type 3 secretion system (T3SS)- and flagellar-related genes in response to green light, genes for the production of phytotoxic lipopeptides and siderophores were significantly reduced by green light. In addition, the phytotoxic lipopeptide and siderophore production in the culture supernatant was consistent with the results of gene expression. Furthermore, we compared the whole transcriptomes of PcJBC1 grown in MM under green light and dark condition. Among 243 differentially expressed genes (>2-fold change), the photoreceptor genes, bacteriophytochrome (bphP) and heme-oxygenase (bphO) were significantly up-regulated, whereas genes involved in the type 1 secretion system (T1SS), type 6 secretion system (T6SS), phytotoxic lipopeptides, and iron acquisition were profoundly repressed under green light. Corresponding to qPCR analysis, the RNA-seq results also showed no significant alteration in the T3SS- and flagellar-related genes. Overall, our results suggest that green light perceived by PcJBC1 plays a key role in diverse physiological responses that might affect this pathogen’s epiphytic survival. The receptor and signaling network involved in green light perception should be identified in further investigation.

Differences of genomic and phenomic responses in resistant and susceptible rice varieties to bacterial leaf blight

April June 2017 892 JCPS Volume 10 Issue 2 Temperature stress mediated oxidative and antioxidant defense in Withania somnifera L. Dunal Mamta Sharma*, Sunil Puri School of Biological and Environmental Sciences has been added, Shoolini University, Solan, HP, India *Corresponding author: E-Mail: diamondmamta@gmail.com, Mobile: 09805330803 ABSTRACT Withania somnifera, a multipurpose medicinal plant of the Himalayan region possesses antioxidant, antitumor, anti-inflammatory, antistress, immunomodulatory, hematopoetic, anti-ageing, anxiolytic, anti-depressive rejuvenating properties and influence various neurotransmitter receptors in the central nervous system. Withanolides, secondary metabolites present in W. somnifera, have neuron regenerative property. In order to evaluate heat stress mediated morphological, physiochemical, oxidative stress and antioxidant defence in the Withania somnifera, plant was subjected to varied temperature conditions. For temperature treatments the seedlings were exposed to five temperature conditions (8 ̊C, 18 ̊C, 38 ̊C, 48 ̊C and 58 ̊C). Seedlings grown at 22 ̊C were treated as control plants. Temperature treatments caused significant decrease in stem length, root length, fresh weight and dry weight in all the treatments. Changes in leaf area, membrane stability and relative water content was also observed and these protein, carotenoids, tocopherol, ascorbic acid and alkaloids decreased. The antioxidant enzymes like superoxide dismutase, catalase, peroxidase, ascorbate peroxidase, glutathione–S-transferase, DPPH (1, 1-diphenyl-2picrylhydrazyl) and ABTS (2, 2’-azino-bis-3ethyl benzthiazoline-6-sulphonic acid) enhanced due to stress treatments. Withanolides were found to be higher in high temperature treated plants. W. somnifera was found to have protective mechanism against oxidative damage by maintaining higher enzymatic and non-enzymatic antioxidants.

A cocktail of volatile compounds emitted from Alcaligenes faecalis JBCS1294 induces salt tolerance in Arabidopsis thaliana by modulating hormonal pathways and ion transporters

In our previous study we showed that volatile organic compounds (VOCs) from Alcaligenes faecalis JBCS1294 (JBCS1294) induced tolerance to salt stress in Arabidopsis thaliana by influencing the auxin and gibberellin pathways and upregulating the expression of key ion transporters. The aim of this study was to evaluate the contribution of each VOC and blends of the VOCs on the induction of salt tolerance and signaling pathways. The key VOCs emitted from JBCS1294 were dissolved in lanolin and applied to one side of bipartite I-plates that contained Arabidopsis seeds on Murashige and Skoog (MS) media supplemented with NaCl on the other side. Changes in plant growth were investigated using Arabidopsis mutant lines and hormone inhibitors, and gene expression was assessed by real-time PCR (qPCR). Among the VOCs, butyric acid conferred salt tolerance over a concentration range of 5.6μM (10ng)-56mM (100μg), whereas propionic and benzoic acid were effective at micromolar doses. Intriguingly, the optimized cocktail of the three VOCs increased fresh weight of Arabidopsis under salt stress compared to that achieved with each single compound. However, Arabidopsis growth was not promoted by the VOCs without salt stress. Exogenous indole-3-acetic acid (IAA) application arrested salt tolerance or growth promotion of Arabidopsis induced by volatiles from propionic acid, but not from butyric acid and an optimized volatile mixture of butyric acid, propionic acid, and benzoic acid (1PBB). High and intense auxin-responsive DR5:GUS activity was observed in the roots of Arabidopsis grown on media without salt via 1PBB, butyric acid, and benzoic acid. Growth promotion by the cocktail was inhibited in the eir1 mutant and in Col-0 plants treated with inhibitors of auxin and gibberellin. The present study clearly demonstrated the effects of individual VOCs and blends of VOCs from a rhizobacterial strain on the induction of salt stress. The results with the blend of VOCs, which mimics bacterial emissions in nature, may lead to a deeper understanding of the interaction between rhizobacteria and plants.