Defensive role of Gossypium hirsutum L. anti-oxidative enzymes and phenolic acids in response to Spodoptera litura F. feeding

The responses of the cotton plant, Gossypium hirsutum L. to herbivory by Spodoptera litura F. was studied in various laboratory experiments as a measure to understand the defense strategies of certain plant metabolites. Insect feeding damage enhanced the concentration of total phenol content and proteins, whereas amount of carbohydrates and amino acids were reduced. The experiments on estimation of anti-oxidative enzymes revealed stimulation in peroxidase, catalase, and superoxide dismutase levels and reduction in polyphenol oxidase and phenylanine ammonia lyase levels, signifying their defensive role in the plant. Specific phenolic acid changes were further carried out using High Performance Liquid Chromatography (HPLC), and distinct elevations in the gallic acid, catechin, and caffeic acid levels were observed in the infested cotton plant. Feeding assays towards S. litura with these phenolic compounds revealed activated detoxifying enzymes including β-glucosidase, carboxyl esterase, and glutathione-S-transferase in the insect gut indicating the toxicity. The aim of present study is to aid in further use of these specific phenolic acids towards effective management of the cotton pest, S. litura.     

A decision-support tool to predict spray deposition of insecticides in commercial potato fields and its implications for their performance

Approximately US $1.3 billion is spent each year on insecticide applications in major row crops. Despite this significant economic importance, there are currently no widely established decision-support tools available to assess suitability of spray application conditions or of the predicted quality or performance of a given commercial insecticide applications. We conducted a field study, involving 14 commercial spray applications with either fixed wing airplane (N=8) or ground rig (N=6), and we used environmental variables as regression fits to obtained spray deposition (coverage in percentage). We showed that (1) ground rig applications provided higher spray deposition than aerial applications, (2) spray deposition was lowest in the bottom portion of the canopy, (3) increase in plant height reduced spray deposition, (4) wind speed increased spray deposition, and (5) higher ambient temperatures and dew point increased spray deposition. Potato psyllid, Bactericera cockerelli (Sulc) (Hemiptera: Triozidae), mortality increased asymptotically to approximately 60% in response to abamectin spray depositions exceeding around 20%, whereas mortality of psyllid adults reached an asymptotic response approximately 40% when lambda-cyhalothrin/thiamethoxam spray deposition exceeded 30%. A spray deposition support tool was developed (http://pilcc.tamu.edu/) that may be used to make decisions regarding (1) when is the best time of day to conduct spray applications and (2) selecting which insecticide to spray based on expected spray deposition. The main conclusion from this analysis is that optimization of insecticide spray deposition should be considered a fundamental pillar of successful integrated pest management programs to increase efficiency of sprays (and therefore reduce production costs) and to reduce risk of resistance development in target pest populations.     

Unusual Constriction Zones in the Major Porins OmpU and OmpT from Vibrio cholerae

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miRNA sensitivity to Drosha levels correlates with pre-miRNA secondary structure

microRNAs (miRNAs) are crucial for cellular development and homeostasis. In order to better understand regulation of miRNA biosynthesis, we studied cleavage of primary miRNAs by Drosha. While Drosha knockdown triggers an expected decrease of many mature miRNAs in human embryonic stem cells (hESC), a subset of miRNAs are not reduced. Statistical analysis of miRNA secondary structure and fold change of expression in response to Drosha knockdown showed that absence of mismatches in the central region of the hairpin, 5 and 9–12 nt from the Drosha cutting site conferred decreased sensitivity to Drosha knockdown. This suggests that, when limiting, Drosha processes miRNAs without mismatches more efficiently than mismatched miRNAs. This is important because Drosha expression changes over cellular development and the fold change of expression for miRNAs with mismatches in the central region correlates with Drosha levels. To examine the biochemical relationship directly, we overexpressed structural variants of miRNA-145, miRNA-137, miRNA-9, and miRNA-200b in HeLa cells with and without Drosha knockdown; for these miRNAs, elimination of mismatches in the central region increased, and addition of mismatches decreased their expression in an in vitro assay and in cells with low Drosha expression. Change in Drosha expression can be a biologically relevant mechanism by which eukaryotic cells control miRNA profiles. This phenomenon may explain the impact of point mutations outside the seed region of certain miRNAs.     

Impact of Plant Phenolics as Semiochemicals on the Performance of <Emphasis Type="Italic">Trichogramma chilonis</Emphasis> Ishii

Phenolic compounds play a major role in the plant defense mechanisms and often offer protection from the feeding herbivore. They also constitute a major chemical component of many agriculturally important crops. We examined the effects of 23 common phenolic acids on the orientation and ovipositional behavior of the egg parasitoid, Trichogramma chilonis Ishii (Hymenoptera: Trichogrammatidae). The study was conducted in order to investigate the function of these compounds in the plant indirect defense. Parasitoids attractions towards the phenolics that are volatile in nature were observed by using culture tube bioassays. In addition in the Y- tube olfactometer experiments, T. chilonis were shown to be attracted towards the treatments of syringic, pyrocatechol, coumaric and quercetin at minimum dose of 10 μg and genistein, chlorogenic, vanillic, chlorobenzoic, sinapic, ellagic, protocatechuic, keampferol, tannic, caffeic, and luteolin at 30 μg and ferulic, epicatechin and gallic acid at 50 μg doses. Further experiments to examine the effect of phenolic compounds on parasitization by T. chilonis females were carried out using petri dish and artificial plant models. Among the tested compounds, syringic acid and quercetin recorded the highest percentage parasitization followed by coumaric acid and pyrocatechol. These results might imply that parasitoid attractant phenolic compounds when induced in engineered plants can further be used as cues by the egg parasitoids with potential application in biocontrol strategies.     

Toll-like Receptor 3-mediated Necrosis via TRIF,RIP3, and MLKL

Toll-like receptor (TLR) signaling is triggered by pathogen-associated molecular patterns that mediate well established cytokine-driven pathways, activating NF-κB together with IRF3/IRF7. In addition, TLR3 drives caspase 8-regulated programmed cell death pathways reminiscent of TNF family death receptor signaling. We find that inhibition or elimination of caspase 8 during stimulation of TLR2, TLR3, TLR4, TLR5, or TLR9 results in receptor interacting protein (RIP) 3 kinase-dependent programmed necrosis that occurs through either TIR domain-containing adapter-inducing interferon-β (TRIF) or MyD88 signal transduction. TLR3 or TLR4 directly activates programmed necrosis through a RIP homotypic interaction motif-dependent association of TRIF with RIP3 kinase (also called RIPK3). In fibroblasts, this pathway proceeds independent of RIP1 or its kinase activity, but it remains dependent on mixed lineage kinase domain-like protein (MLKL) downstream of RIP3 kinase. Here, we describe two small molecule RIP3 kinase inhibitors and employ them to demonstrate the common requirement for RIP3 kinase in programmed necrosis induced by RIP1-RIP3, DAI-RIP3, and TRIF-RIP3 complexes. Cell fate decisions following TLR signaling parallel death receptor signaling and rely on caspase 8 to suppress RIP3-dependent programmed necrosis whether initiated directly by a TRIF-RIP3-MLKL pathway or indirectly via TNF activation and the RIP1-RIP3-MLKL necroptosis pathway.     

Role of castor plant phenolics on performance of its two herbivores and their impact on egg parasitoid behaviour

Plants are reported to reconfigure their metabolism and generate secondary metabolites as a defence response towards herbivore attack. In this study we aimed to evaluate the anti-nutritive and defensive properties of phenolic compounds that were enhanced in Castor, Ricinus communis L. plant due to herbivore damage. Through HPLC studies it was observed that damage caused by two pests, Achaea janata L. and Spodoptera litura F. on the castor plant resulted in quantitative enhancement of syringic, coumaric, cinnamic and vanillic acids. These phenolic compounds showed considerable impact on insect’s feeding and their toxic nature towards the herbivores was determined by estimating three detoxification mid-gut enzymes, glutathione-s-transferase, carboxyl esterase and β-glucosidase. In the ovipositional and orientation bioassays with the egg parasitoid Trichogramma chilonis Ishii, syringic and coumaric acids had shown good kairomonal activity, thus defining a new role of these chemicals in indirect plant defence. Thus, this study demonstrates a quantitative association between plant phenolic accumulation and the elevated reproductive performance of the herbivore natural enemies, by illustrating the role of plant phenolics in both the direct and indirect induced plant defences.