A paratransgenic strategy to block transmission of Xylella fastidiosa from the glassy-winged sharpshooter Homalodisca vitripennis

Horizon scanning of potential environmental applications of terrestrial animals, fish, algae and microorganisms produced by genetic modification, including the use of new genomic techniques

With scientific progress and the development of new genomic techniques (NGTs), the spectrum of organisms modified for various purposes is rapidly expanding and includes a wide range of taxonomic groups. An improved understanding of which newly developed products may be introduced into the market and released into the environment in the near and more distant future is of particular interest for policymakers, regulatory authorities, and risk assessors. To address this information need, we conducted a horizon scanning (HS) of potential environmental applications in four groups of organisms: terrestrial animals (excluding insects and applications with gene drives), fish, algae and microorganisms. We applied a formal scoping review methodology comprising a structured search of the scientific literature followed by eligibility screening, complemented by a survey of grey literature, and regulatory websites and databases. In all four groups of organisms we identified a broad range of potential applications in stages of basic as well as advanced research, and a limited number of applications which are on, or ready to be placed on, the market. Research on GM animals including fish is focused on farmed animals and primarily targets traits which increase performance, influence reproduction, or convey resistance against diseases. GM algae identified in the HS were all unicellular, with more than half of the articles concerning biofuel production. GM algae applications for use in the environment include biocontrol and bioremediation, which are also the main applications identified for GM microorganisms. From a risk assessor's perspective these potential applications entail a multitude of possible pathways to harm. The current limited level of experience and limited amount of available scientific information could constitute a significant challenge in the near future, for which risk assessors and competent authorities urgently need to prepare.

Functional Peptides for Plant Disease Control

Plant disease control requires novel approaches to mitigate the spread of and losses caused by current, emerging, and re-emerging diseases and to adapt plant protection to global climate change and the restrictions on the use of conventional pesticides. Currently, disease management relies mainly on biopesticides, which are required for the sustainable use of plant-protection products. Functional peptides are candidate biopesticides because they originate from living organisms or are synthetic analogs and provide novel mechanisms of action against plant pathogens. Hundreds of compounds exist that cover an extensive range of activities against viruses, bacteria and phytoplasmas, fungi and oomycetes, and nematodes. Natural sources, chemical synthesis, and biotechnological platforms may provide peptides at large scale for the industry and growers. The main challenges for their use in plant disease protection are (a) the requirement of stability in the plant environment and counteracting resistance in pathogen populations, (b) the need to develop suitable formulations to increase their shelf life and methods of application, (c) the selection of compounds with acceptable toxicological profiles, and (d) the high cost of production for agricultural purposes. In the near future, it is expected that several functional peptides will be commercially available for plant disease control, but more effort is needed to validate their efficacy at the field level and fulfill the requirements of the regulatory framework.

Facultative symbionts are potential agents of symbiont-mediated RNAi in aphids

Aphids are major crop pests, and they can be controlled through the application of the promising RNA interference (RNAi) techniques. However, chemical synthesis yield of dsRNA for RNAi is low and costly. Another sustainable aphid pest control strategy takes advantage of symbiont-mediated RNAi (SMR), which can generate dsRNA by engineered microbes. Aphid host the obligate endosymbiont Buchnera aphidicola and various facultative symbionts that not only have a wide host range but are also vertically and horizontally transmitted. Thus, we described the potential of facultative symbionts in aphid pest control by SMR. We summarized the community and host range of these facultative symbionts, and then reviewed their probable horizontal transmitted routes and ecological functions. Moreover, recent advances in the cultivation and genetic engineering of aphid facultative symbionts were discussed. In addition, current legislation of dsRNA-based pest control strategies and their safety assessments were reviewed.

Effects of feeding on different parts of Ailanthus altissima on the intestinal microbiota of Eucryptorrhynchus scrobiculatus and Eucryptorrhynchus brandti (Coleoptera: Curculionidae)

Eucryptorrhynchus brandti and Eucryptorrhynchus scrobiculatus (Coleoptera: Curculionidae) are two monophagous weevil pests that feed on Ailanthus altissima (Mill.) Swingle but differ in their diet niche. In the field, adults of E. brandti prefer to feed on the trunk of A. altissima, whereas adults of E. scrobiculatus prefer to feed on the tender parts. We conducted Illumina sequencing of 16S rRNA to examine changes in bacterial diversity in the adults of these two weevil species after they fed on different parts of A. altissima (trunk, 2–3-year-old branches, annual branches, and petioles). Proteobacteria, Tenericutes, and Firmicutes were the dominant phyla in E. brandti (relative abundance was 50.64, 41.56, and 5.63%, respectively) and E. scrobiculatus (relative abundance was 78.63, 11.91, and 7.41%, respectively). At the genus level, Spiroplasma, endosymbionts2, Unclassified Enterobacteriaceae, and Lactococcus were dominant in E. brandti, and Unclassified Enterobacteriaceae, Wolbachia and Spiroplasma, and endosymbionts2 were dominant in E. scrobiculatus. Linear discriminant analysis effect size analysis revealed microbial biomarkers in the different treatment group of adults of both weevil species. Adults of E. brandti may require the trunk, and adults of E. scrobiculatus may require the petioles and annual branches to maintain the high diversity of their gut microbes. The results of this study indicate that feeding on different parts of A. altissima affects the composition and function of the microbes of E. brandti and the microbial composition of E. scrobiculatus. Variation in the abundance of Wolbachia and Spiroplasma in E. brandti and E. scrobiculatus is associated with dietary niche changes, and this might explain the evolution of reproductive isolation between these two sibling weevil species.

Thidiazuron: New Trends and Future Perspectives to Fight Xylella fastidiosa in Olive Trees

These days, most of our attention has been focused on the COVID-19 pandemic, and we have often neglected what is happening in the environment. For instance, the bacterium Xylella fastidiosa re-emerged as a plant pathogen of global importance in 2013 when it was first associated with an olive tree disease epidemic in Italy, called Olive Quick Decline Syndrome (OQDS), specifically caused by X. fastidiosa subspecies pauca ST53, which affects the Salento olive trees (Apulia, South-East Italy). This bacterium, transmitted by the insect Philaenus spumarius, is negatively reshaping the Salento landscape and has had a very high impact in the production of olives, leading to an increase of olive oil prices, thus new studies to curb this bacterium are urgently needed. Thidiazuron (TDZ), a diphenylurea (N-phenyl-1,2,3-thiadiazol-5-yl urea), has gained considerable attention in recent decades due to its efficient role in plant cell and tissue culture, being the most suitable growth regulator for rapid and effective plant production in vitro. Its biological activity against bacteria, fungi and biofilms has also been described, and the use of this low-cost compound to fight OQDS may be an intriguing idea.

Metatranscriptomic Assessment of the Microbial Community Associated With the Flavescence dorée Phytoplasma Insect Vector Scaphoideus titanus

Phytoplasmas are insect-borne pathogenic bacteria that cause major economic losses to several crops worldwide. The dynamic microbial community associated with insect vectors influences several aspects of their biology, including their vector competence for pathogens. Unraveling the diversity of the microbiome of phytoplasma insect vectors is gaining increasing importance in the quest to develop novel microbe-based pest control strategies that can minimize the use of insecticides for better environmental quality. The leafhopper Scaphoideus titanus is the primary vector of the Flavescence dorée phytoplasma, a quarantine pest which is dramatically affecting the main grape-growing European countries. In this study, the RNA-Seq data, which were previously used for insect virus discovery, were further explored to assess the composition of the whole microbial community associated with insects caught in the wild in both its native (the United States) and invasive (Europe) areas. The first de novo assembly of the insect transcriptome was used to filter the host sequencing reads. The remaining ones were assembled into contigs and analyzed by blastx to provide the taxonomic identification of the microorganisms associated with S. titanus, including the non-bacterial components. By comparing the transcriptomic libraries, we could differentiate the stable and consistent associations from the more ephemeral and flexible ones. Two species appeared to be universal to the core microbiome of S. titanus: the obligate bacterial symbiont Candidatus Sulcia muelleri and an Ophiocordyceps-allied fungus distantly related to yeast-like symbionts described from other hemipterans. Bacteria of the genus Cardinium have been identified as another dominant member of the microbiome, but only in the European specimens. Although we are yet to witness how the interplay among the microorganisms influences the vector competence of S. titanus, this unbiased in silico characterization of its microbiome is paramount for identifying the naturally occurring targets for new biocontrol strategies to counteract Flavescence dorée spread in Europe.

Applications and evolution of melittin, the quintessential membrane active peptide

Melittin, the main venom component of the European Honeybee, is a cationic linear peptide-amide of 26 amino acid residues with the sequence: GIGAVLKVLTTGLPALISWIKRKRQQ-NH₂. Melittin binds to lipid bilayer membranes, folds into amphipathic α-helical secondary structure and disrupts the permeability barrier. Since melittin was first described, a remarkable array of activities and potential applications in biology and medicine have been described. Melittin is also a favorite model system for biophysicists to study the structure, folding and function of peptides and proteins in membranes. Melittin has also been used as a template for the evolution of new activities in membranes. Here we overview the rich history of scientific research into the many activities of melittin and outline exciting future applications.

Engineering insects from the endosymbiont out

Insects are an incredibly diverse group of animals with species that benefit and harm natural ecosystems, agriculture, and human health. Many insects have consequential associations with microbes: bacterial symbionts may be embedded in different insect tissues and cell types, inherited across insect generations, and required for insect survival and reproduction. Genetically engineering insect symbionts is key to understanding and harnessing these associations. We summarize different types of insect-bacteria relationships and review methods used to genetically modify endosymbiont and gut symbiont species. Finally, we discuss recent studies that use this approach to study symbioses, manipulate insect-microbe interactions, and influence insect biology. Further progress in insect symbiont engineering promises to solve societal challenges, ranging from controlling pests to protecting pollinator health.

Engineering a Culturable Serratia symbiotica Strain for Aphid Paratransgenesis

Aphids are global agricultural pests and important models for bacterial symbiosis. To date, none of the native symbionts of aphids have been genetically manipulated, which limits our understanding of how they interact with their hosts. Serratia symbiotica CWBI-2.3T is a culturable, gut-associated bacterium isolated from the black bean aphid. Closely related Serratia symbiotica strains are facultative aphid endosymbionts that are vertically transmitted from mother to offspring during embryogenesis. We demonstrate that CWBI-2.3T can be genetically engineered using a variety of techniques, plasmids, and gene expression parts. Then, we use fluorescent protein expression to track the dynamics with which CWBI-2.3T colonizes the guts of multiple aphid species, and we measure how this bacterium affects aphid fitness. Finally, we show that we can induce heterologous gene expression from engineered CWBI-2.3T in living aphids. These results inform the development of CWBI-2.3T for aphid paratransgenesis, which could be used to study aphid biology and enable future agricultural technologies.IMPORTANCE Insects have remarkably diverse and integral roles in global ecosystems. Many harbor symbiotic bacteria, but very few of these bacteria have been genetically engineered. Aphids are major agricultural pests and an important model system for the study of symbiosis. This work describes methods for engineering a culturable aphid symbiont, Serratia symbiotica CWBI-2.3T These approaches and genetic tools could be used in the future to implement new paradigms for the biological study and control of aphids.

Nutritional Relationship between Bemisia tabaci and Its Primary Endosymbiont, Portiera aleyrodidarum, during Host Plant Acclimation

Simple Summary

Plant sap-sucking insects commonly have established mutualistic relationships with bacteria that live within their bodies and often provide nutrients that are lacking in the insect’s diet. The sweet potato whitefly (Bemisia tabaci) harbors one primary and up to seven secondary endosymbiotic bacteria. The primary endosymbiont of B. tabaci is already known to play a critical role in providing necessary nutrients for B. tabaci. Our objective was to study the relationship among B. tabaci, its primary endosymbiont, and the host plant through the effects of host plant shifting and acclimation, that is, physiological adjustments as an insect becomes accustomed to a new host plant over several generations. The results showed that host shifting from Chinese kale to cotton plants led to a decrease in the fecundity of B. tabaci in the first generation, which was restored after 10 generations of acclimation, and that its developmental time was also decreased by the tenth generation. Furthermore, essential amino acid biosynthesis genes of its primary endosymbiont were differentially regulated after B. tabaci had become acclimated to cotton plants. We speculate that the primary endosymbiont has a close nutritional relationship with B. tabaci during host plant acclimation.

Abstract

Plant sap-sucking insects commonly have established mutualistic relationships with endosymbiotic bacteria that can provide nutrients lacking in their diet. Bemisia tabaci harbors one primary endosymbiont, Portiera aleyrodidarum, and up to seven secondary endosymbionts, including Hamiltonella defensa and Rickettsia sp. Portiera aleyrodidarum is already known to play a critical role in providing necessary nutrients for B. tabaci. In the present study, the relationship among B. tabaci, its primary endosymbiont, and the host plant were examined through the effects of host plant shifting and acclimation. Bemisia tabaci was transferred from Chinese kale to four different host plants, and the effects on both its performance and the expression levels of nutrient-related genes of P. aleyrodidarum were analyzed. The results showed that host shifting from Chinese kale to cotton plants led to a decrease in the performance of B. tabaci in the first generation, which was restored after 10 generations of acclimation. Furthermore, the expression levels of essential amino acid biosynthesis genes of P. aleyrodidarum were found to be differentially regulated after B. tabaci had acclimated to the cotton plants. Host plant shifting and acclimation to cucumber, poinsettia, and tomato plants did not affect the fecundity of B. tabaci and the expression levels of most examined genes. We speculate that P. aleyrodidarum may help B. tabaci improve its performance and acclimate to new hosts and that P. aleyrodidarum has a close nutritional relationship with its host during host plant acclimation.

From Nucleotides to Satellite Imagery: Approaches to Identify and Manage the Invasive Pathogen Xylella fastidiosa and Its Insect Vectors in Europe

Biological invasions represent some of the most severe threats to local communities and ecosystems. Among invasive species, the vector-borne pathogen Xylella fastidiosa is responsible for a wide variety of plant diseases and has profound environmental, social and economic impacts. Once restricted to the Americas, it has recently invaded Europe, where multiple dramatic outbreaks have highlighted critical challenges for its management. Here, we review the most recent advances on the identification, distribution and management of X. fastidiosa and its insect vectors in Europe through genetic and spatial ecology methodologies. We underline the most important theoretical and technological gaps that remain to be bridged. Challenges and future research directions are discussed in the light of improving our understanding of this invasive species, its vectors and host–pathogen interactions. We highlight the need of including different, complimentary outlooks in integrated frameworks to substantially improve our knowledge on invasive processes and optimize resources allocation. We provide an overview of genetic, spatial ecology and integrated approaches that will aid successful and sustainable management of one of the most dangerous threats to European agriculture and ecosystems.

An integrative approach to symbiont-mediated vector control for agricultural pathogens

Vector-borne pathogens pose significant threats to agricultural productivity. Methods that exploit associations between insects and their symbiotic microbes, dubbed symbiont-mediated vector control, are emerging as viable alternatives to insecticides for the control of vector-borne agricultural plant pathogens. The development of methods for effective microbial manipulation, such as RNA interference and paratransgenesis, may facilitate symbiont-mediated vector control tactics aimed at either suppressing insect populations or at manipulating vector competence, an insect vector's ability to acquire, harbor, and transmit pathogens. As suppression strategies transition from the laboratory to the field, the need for methods to evaluate their viability and predict their outcomes is apparent. Mathematical models of symbiont impact on agricultural disease can inform the development of symbiont-mediated vector control. We propose an integrative approach, combining theoretical and empirical experiments to identify the best practices for achieving meaningful improvements to crop health and productivity.