The Commonly Used Bactericide Bismerthiazol Promotes Rice Defenses against Herbivores

Quorum sensing in biofilms: a key mechanism to target in ecotoxicological studies

Our environment is heavily contaminated by anthropogenic compounds, and this issue constitutes a significant threat to all life forms, including biofilm-forming microorganisms. Cell-cell interactions shape microbial community structures and functions, and pollutants that affect intercellular communications impact biofilm functions and ecological roles. There is a growing interest in environmental science fields for evaluating how anthropogenic pollutants impact cell-cell interactions. In this review, we synthesize existing literature that evaluates the impacts of quorum sensing (QS), which is a widespread density-dependent communication system occurring within many bacterial groups forming biofilms. First, we examine the perturbating effects of environmental contaminants on QS circuits; and our findings reveal that QS is an essential yet underexplored mechanism affected by pollutants. Second, our work highlights that QS is an unsuspected and key resistance mechanism that assists bacteria in dealing with environmental contamination (caused by metals or organic pollutants) and that favors bacterial growth in unfavourable environments. We emphasize the value of considering QS a critical mechanism for monitoring microbial responses in ecotoxicology. Ultimately, we determine that QS circuits constitute promising targets for innovative biotechnological approaches with major perspectives for applications in the field of environmental science.

Four-Chlorophenoxyacetic Acid Treatment Induces the Defense Resistance of Rice to White-Backed Planthopper Sogatella furcifera

Chemical elicitors can increase plant defense against herbivorous insects and pathogens. The use of synthetic chemical elicitors is likely to be an alternative to traditional pesticides for crop pest control. However, only a few synthetic chemicals are reported to protect plants by regulating signaling pathways, increasing the levels of defense metabolites and interfering with insect feeding. Here, we found that the exogenous application of a phenoxycarboxylic compound, 4-chlorophenoxyacetic acid (4-CPA), can induce chemical defenses to protect rice plants from white-backed planthoppers (WBPH, Sogatella furcifera). Four-CPA was rapidly taken up by plant roots and degraded to 4-chlorophenol (4-CP). Four-CPA treatment modulated the activity of peroxidase (POD) and directly induced the deposition of lignin-like polymers using hydrogen peroxide (H2O2) as the electron acceptor. The polymers, which are thought to prevent the planthopper's stylet from reaching the phloem, were broken down by WBPH nymphs. Meanwhile, 4-CPA increased the levels of flavonoids and phenolamines (PAs). The increased flavonoids and PAs, together with the degradation product of the polymers, avoided nymphal feeding and prolonged the nymphal period for 1 day. These results indicate that 4-CPA has the potential to be used as a chemical elicitor to protect rice from planthoppers. Moreover, these findings also open a pathway for molecule structure design of phenoxycarboxylic compounds as chemical elicitors.

Ethylicin Inhibition of Xanthomonas oryzae pv. oryzicola In Vitro and In Vivo

Infestation of rice with the bacterium Xanthomonas oryzae pv. oryzicola (Xoc) causes the serious disease bacterial leaf streak (BLS). We studied the effect of ethylicin, a broad-spectrum bactericide, on Xoc both in vivo and in vitro. Ethylicin increases the defensive enzyme activities and defensive genes expression of rice. Ethylicin also significantly inhibited Xoc activity in vitro compared with other commercial bactericides. The half-maximal effective concentration (EC₅₀) of ethylicin was 2.12 μg/mL. It has been shown that ethylicin can inhibit Xoc quorum sensing through the production of extracellular polysaccharides and enzymes, which disrupt the Xoc cell membrane. We used proteomic analysis to identify two oxidative phosphorylation pathway proteins (ACU12_RS13405 and ACU12_RS13355) which affected the virulence of Xoc and validated them using quantitative real-time polymerase chain reaction (qRT-PCR). The results indicate that ethylicin can increase the defense responses of rice and control Xoc proliferation.

Plant elicitor peptide signalling confers rice resistance to piercing-sucking insect herbivores and pathogens

Rice is a staple food crop worldwide, and its production is severely threatened by phloem-feeding insect herbivores, particularly the brown planthopper (BPH, Nilaparvata lugens), and destructive pathogens. Despite the identification of many BPH resistance genes, the molecular basis of rice resistance to BPH remains largely unclear. Here, we report that the plant elicitor peptide (Pep) signalling confers rice resistance to BPH. Both rice PEP RECEPTORs (PEPRs) and PRECURSORs of PEP (PROPEPs), particularly OsPROPEP3, were transcriptionally induced in leaf sheaths upon BPH infestation. Knockout of OsPEPRs impaired rice resistance to BPH, whereas exogenous application of OsPep3 improved the resistance. Hormone measurement and co-profiling of transcriptomics and metabolomics in OsPep3-treated rice leaf sheaths suggested potential contributions of jasmonic acid biosynthesis, lipid metabolism and phenylpropanoid metabolism to OsPep3-induced rice immunity. Moreover, OsPep3 elicitation also strengthened rice resistance to the fungal pathogen Magnaporthe oryzae and bacterial pathogen Xanthamonas oryzae pv. oryzae and provoked immune responses in wheat. Collectively, this work demonstrates a previously unappreciated importance of the Pep signalling in plants for combating piercing-sucking insect herbivores and promises exogenous application of OsPep3 as an eco-friendly immune stimulator in agriculture for crop protection against a broad spectrum of insect pests and pathogens.

Exogenous Application of Gallic Acid Induces the Direct Defense of Tea Plant Against Ectropis obliqua Caterpillars

Gallic acid (GA), an important polyphenolic compound in the plant, is a well-known antioxidant, antihyperglycemic, and anti-lipid peroxidative agent. Recently, GA treatment exhibited ameliorative effects on plants in response to some abiotic stresses. However, the elicitation effect of GA on plant defense against herbivorous insects has not yet been reported. In this study, we found that the exogenous application of GA induced the direct defense of tea plant (Camellia sinensis) against tea geometrid (Ectropis obliqua) larvae, through activating jasmonic acid (JA) signaling and phenylpropanoid pathways. These signaling cascades resulted in the efficient induction of several defensive compounds. Among them, astragalin, naringenin, and epigallocatechin-3-gallate were the three of the most active anti-feeding compounds. However, the exogenous GA treatment did not affect the preference of E. obliqua female moths and larval parasitoid Apanteles sp. Our study suggests that GA may serve as an elicitor that triggers a direct defense response against tea geometrid larvae in tea plants. This study will help to deepen the understanding of the interaction between plants and phytophagous insects and also provide theoretical and technical guidance for the development of plant defense elicitors.

Quantitative assessment of the nature of noncovalent interactions in N-substituted-5-(adamantan-1-yl)-1,3,4-thiadiazole-2-amines: insights from crystallographic and QTAIM analysis

Three adamantane-1,3,4-thiadiazole hybrid derivatives namely; N-ethyl-5-(adamantan-1-yl)-1,3,4-thiadiazole-2-amine I, N-(4-fluorophenyl)-5-(adamantan-1-yl)-1,3,4-thiadiazole-2-amine II and (4-bromophenyl)-5-(adamantan-1-yl)-N-1,3,4-thiadiazole-2-amine III, have been synthesized and crystal structures have been determined at low temperature. The structures revealed that the orientation of the amino group is different in non-halogenated structures. Intra- and intermolecular interactions were characterized on the basis of the quantum theory of atoms-in-molecules (QTAIM) approach. Intermolecular interaction energies for different molecular pairs have been obtained using the PIXEL method. Hirshfeld surface analysis and 2D-fingerprint plots revealed that the relative contributions of different non-covalent interactions are comparable in compounds with halogen (Br and F) substitutions. Crystal structures of II and III show isostructural behaviour with 1D supramolecular constructs. In all three structures, the N-H⋯N hydrogen bond was found to be stronger among other noncovalent interactions. The H-H bonding showed a closed shell in nature and played significant roles in the stabilization of these crystal structures.

Current understanding of the molecular players involved in resistance to rice planthoppers

Rice planthoppers are the most widespread and destructive pest of rice. Planthopper control depends greatly on the understanding of molecular players involved in resistance to planthoppers. This paper summarizes the recent progress in the understanding of some molecular players involved in resistance to planthoppers and the mechanisms involved. Recent researches showed that host-plant resistance is the most promising sustainable approach for controlling planthoppers. Planthopper-resistant varieties with a host-plant resistance gene have been released for rice products. Integrated planthopper management is a proposed strategy to prolong the durability of host-plant resistance. Bacillus spp. and their gene products or insect pathogenic fungi have great potential for application in the biological control of planthoppers. Enhancement of the activity of the natural enemies of planthoppers would be more cost-effective and environmentally friendly. Various molecular processes regulate rice-planthopper interactions. Rice encounters planthopper attacks via transcription factors, secondary metabolites, and signaling networks in which phytohormones have central roles. Maintenance of cell wall integrity and lignification act as physical barriers. Indirect defenses of rice are regulated via chemical elicitors, honeydew-associated elicitor, amendment with silicon and biochar, and salivary protein of BPH as elicitor or effector. Further research directions on planthopper control and rice defense against planthoppers are also put forward. © 2019 Society of Chemical Industry.

OsMKK3, a Stress-Responsive Protein Kinase, Positively Regulates Rice Resistance to Nilaparvata lugens via Phytohormone Dynamics

Plants undergo several but very precise molecular, physiological, and biochemical modulations in response to biotic stresses. Mitogen-activated protein kinase (MAPK) cascades orchestrate multiple cellular processes including plant growth and development as well as plant responses against abiotic and biotic stresses. However, the role of MAPK kinases (MAPKKs/MKKs/MEKs) in the regulation of plant resistance to herbivores has not been extensively investigated. Here, we cloned a rice MKK gene, OsMKK3, and investigated its function. It was observed that mechanical wounding, infestation of brown planthopper (BPH) Nilaparvata lugens, and treatment with methyl jasmonate (MeJA) or salicylic acid (SA) could induce the expression of OsMKK3. The over-expression of OsMKK3 (oe-MKK3) increased levels of jasmonic acid (JA), jasmonoyl-L-isoleucine (JA-Ile), and abscisic acid (ABA), and decreased SA levels in rice after BPH attack. Additionally, the preference for feeding and oviposition, the hatching rate of BPH eggs, and BPH nymph survival rate were significantly compromised due to over-expression of OsMKK3. Besides, oe-MKK3 also augmented chlorophyll content but impaired plant growth. We confirm that MKK3 plays a pivotal role in the signaling pathway. It is proposed that OsMKK3 mediated positive regulation of rice resistance to BPH by means of herbivory-induced phytohormone dynamics.