Aphids

Enhancing protein signal detection in asexual and viviparous pea aphids: A guided protocol for tissue dissection and proteinase K treatment

Aphids, as hemipteran insects, reproduce via parthenogenesis and viviparity, resulting in rapid and exponential offspring production. To investigate the molecular mechanisms underlying parthenogenetic viviparity in asexual aphids, precise protein detection through immunostaining is essential. Our previous research demonstrated the need for proteinase K (PK) treatment to improve tissue permeability, enabling antibodies targeting the germ-cell marker Ap-Vas1 to access gastrulating and later-stage embryos. However, optimal PK digestion protocols have not been thoroughly explored. In this study, we propose strategies to optimize PK digestion conditions for early, middle, and late-stage pea aphid embryos, which have varying tissue thicknesses. Additionally, we extend the application of PK treatment to salivary glands, a representative somatic tissue, by optimizing conditions for antibody penetration against the salivary gland marker C002. To enhance spatial precision in signal detection, we provide a detailed protocol for tissue dissection specific to pea aphids, focusing on the preservation of tissue integrity. These comprehensive guidelines, covering tissue dissection and PK titration, are expected to improve the specificity and intensity of protein signals in pea aphids and other aphid species.•Provide aphid-specific dissection methods to obtain intact embryos and salivary glands.•Present strategies for optimizing PK treatment conditions across different tissue types.

Candidate genes potentially involved in molting and body size reduction in the male of the horned gall aphid, Schlechtendalia chinensis

In general, insects grow (increase in body size) through molting. To the opposite, the body size of the males of the horned gall aphid, Schlechtendalia chinensis, gets smaller after molting and as they age. To understand the molecular bases of this rare phenomenon, transcriptomes were generated from 1-5 days old male and the data were analyzed via a weighted gene co-expression network analysis (WGCNA). A total of 15 partitioned modules with different topological overlaps were obtained, and four modules were identified as highly significant for male body length (p < 0.05). Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis suggested that a portion of genes in the four modules are likely involved in autophagy and apoptosis. In addition, a total of 40 hub genes were obtained in the four modules, and among them eight genes were highly expressed in males compared to individuals of other generations of S. chinensis. These eight genes were associated with autophagy and apoptosis. Our results reveal the unique negative growth phenomenon in male S. chinensis after molting, and also suggest that the male S. chinensis with no ability to feed probably decompose their own substances via autophagy and apoptosis to provide energy for life activities such as germ cell development.

Spring phenology and pathogen infection affect multigenerational plant attackers throughout the growing season

Climate change has been shown to advance spring phenology, increase the number of insect generations per year (multivoltinism) and increase pathogen infection levels. However, we lack insights into the effects of plant spring phenology and the biotic environment on the preference and performance of multivoltine herbivores and whether such effects extend into the later part of the growing season. To this aim, we used a multifactorial growth chamber experiment to examine the influence of spring phenology on plant pathogen infection, and how the independent and interactive effects of spring phenology and plant pathogen infection affect the preference and performance of multigenerational attackers (the leaf miner Tischeria ekebladella and the aphid Tuberculatus annulatus) on the pedunculate oak in the early, mid and late parts of the plant growing season. Pathogen infection was highest on late phenology plants, irrespective of whether inoculations were conducted in the early, mid or late season. The leaf miner consistently preferred to oviposit on middle and late phenology plants, as well as healthy plants, during all parts of the growing season, whereas we detected an interactive effect between spring phenology and pathogen infection on the performance of the leaf miner. Aphids preferred healthy, late phenology plants during the early season, healthy plants during the mid season, and middle phenology plants during the late season, whereas aphid performance was consistently higher on healthy plants during all parts of the growing season. Our findings highlight that the impact of spring phenology on pathogen infection and the preference and performance of insect herbivores is not restricted to the early season, but that its imprint is still present - and sometimes equally strong - during the peak and end of the growing season. Plant pathogens generally negatively affected herbivore preference and performance, and modulated the effects of spring phenology. We conclude that spring phenology and pathogen infection are two important factors shaping the preference and performance of multigenerational plant attackers, which is particularly relevant given the current advance in spring phenology, pathogen outbreaks and increase in voltinism with climate change.

Germline specification and axis determination in viviparous and oviparous pea aphids: conserved and divergent features

Aphids are hemimetabolous insects that undergo incomplete metamorphosis without pupation. The annual life cycle of most aphids includes both an asexual (viviparous) and a sexual (oviparous) phase. Sexual reproduction only occurs once per year and is followed by many generations of asexual reproduction, during which aphids propagate exponentially with telescopic development. Here, we discuss the potential links between viviparous embryogenesis and derived developmental features in the pea aphid Acyrthosiphon pisum, particularly focusing on germline specification and axis determination, both of which are key events of early development in insects. We also discuss potential evolutionary paths through which both viviparous and oviparous females might have come to utilize maternal germ plasm to drive germline specification. This developmental strategy, as defined by germline markers, has not been reported in other hemimetabolous insects. In viviparous females, furthermore, we discuss whether molecules that in other insects characterize germ plasm, like Vasa, also participate in posterior determination and how the anterior localization of the hunchback orthologue Ap-hb establishes the anterior-posterior axis. We propose that the linked chain of developing oocytes and embryos within each ovariole and the special morphology of early embryos might have driven the formation of evolutionary novelties in germline specification and axis determination in the viviparous aphids. Moreover, based upon the finding that the endosymbiont Buchnera aphidicola is closely associated with germ cells throughout embryogenesis, we propose presumptive roles for B. aphidicola in aphid development, discussing how it might regulate germline migration in both reproductive modes of pea aphids. In summary, we expect that this review will shed light on viviparous as well as oviparous development in aphids.

Comparative Transcriptome Analysis Reveals Genetic Mechanisms of Sugarcane Aphid Resistance in Grain Sorghum

The sugarcane aphid, Melanaphis sacchari (Zehntner) (Hemiptera: Aphididae) (SCA), has become a major pest of grain sorghum since its appearance in the USA. Several grain sorghum parental lines are moderately resistant to the SCA. However, the molecular and genetic mechanisms underlying this resistance are poorly understood, which has constrained breeding for improved resistance. RNA-Seq was used to conduct transcriptomics analysis on a moderately resistant genotype (TAM428) and a susceptible genotype (Tx2737) to elucidate the molecular mechanisms underlying resistance. Differential expression analysis revealed differences in transcriptomic profile between the two genotypes at multiple time points after infestation by SCA. Six gene clusters had differential expression during SCA infestation. Gene ontology enrichment and cluster analysis of genes differentially expressed after SCA infestation revealed consistent upregulation of genes controlling protein and lipid binding, cellular catabolic processes, transcription initiation, and autophagy in the resistant genotype. Genes regulating responses to external stimuli and stress, cell communication, and transferase activities, were all upregulated in later stages of infestation. On the other hand, expression of genes controlling cell cycle and nuclear division were reduced after SCA infestation in the resistant genotype. These results indicate that different classes of genes, including stress response genes and transcription factors, are responsible for countering the physiological effects of SCA infestation in resistant sorghum plants.

Evolutionary conservation of the antimicrobial function of mucus: a first defence against infection

Mucus layers often provide a unique and multi-functional hydrogel interface between the epithelial cells of organisms and their external environment. Mucus has exceptional properties including elasticity, changeable rheology and an ability to self-repair by re-annealing, and is therefore an ideal medium for trapping and immobilising pathogens and serving as a barrier to microbial infection. The ability to produce a functional surface mucosa was an important evolutionary step, which evolved first in the Cnidaria, which includes corals, and the Ctenophora. This allowed the exclusion of non-commensal microbes and the subsequent development of the mucus-lined digestive cavity seen in higher metazoans. The fundamental architecture of the constituent glycoprotein mucins is also evolutionarily conserved. Although an understanding of the biochemical interactions between bacteria and the mucus layer are important to the goal of developing new antimicrobial strategies, they remain relatively poorly understood. This review summarises the physicochemical properties and evolutionary importance of mucus, which make it so successful in the prevention of bacterial infection. In addition, the strategies developed by bacteria to counteract the mucus layer are also explored.

Reliable protocols for whole-mount fluorescent in situ hybridization (FISH) in the pea aphid Acyrthosiphon pisum: a comprehensive survey and analysis

RNA in situ hybridization (ISH), including chromogenic ISH (CISH) and fluorescent ISH (FISH), has become a powerful tool for revealing the spatial distribution of gene transcripts in model organisms. Previously, we developed a robust protocol for whole-mount RNA CISH in the pea aphid Acyrthosiphon pisum, an emerging insect genomic model. In order to improve the resolving capacity of gene detection, we comprehensively surveyed current protocols of whole-mount RNA-FISH and developed protocols that allow, using confocal microscopy, clearer visualization of target messenger RNAs (mRNAs) - including those subcellularly localized and those with spatially overlapping expression. We find that Fast dye-based substrate fluorescence (SF), tyramide signal amplification (TSA), and TSA Plus all enable identifying gene expression thanks to multiplex amplification of fluorescent signals. By contrast, methods of direct fluorescence (DF) do not allow visualizing signals. Detection of a single gene target was achieved with SF and TSA Plus for most mRNAs, whereas TSA only allowed visualization of abundant transcripts such as Apvas1 and Appiwi2 in the germ cells. For detection of multiple gene targets using double FISH, we recommend: (i) TSA/TSA, rather than TSA Plus/TSA Plus for colocalized mRNAs abundantly expressed in germ cells, as proteinase K treatment can be omitted; and (ii) SF/TSA Plus for other gene targets such as Apen1 and Apen2 as inactivation of enzyme conjugates is not required. SF/SF is not ideal for double FISH experiments due to signal blurring. Based on these new conditions for RNA-FISH, we have obtained a better understanding of germline specification and embryonic segmentation in the pea aphid. We anticipate that the RNA-FISH protocols for the pea aphid may also be used for other aphids and possibly other insect species, thus expanding the range of species from which useful insights into development and evolution may be obtained.

Halloween genes and nuclear receptors in ecdysteroid biosynthesis and signalling in the pea aphid

The pea aphid (Acyrthosiphon pisum) is the first whole genome sequenced insect with a hemimetabolic development and an emerging model organism for studies in ecology, evolution and development. The insect steroid moulting hormone 20-hydroxyecdysone (20E) controls and coordinates development in insects, especially the moulting/metamorphosis process. We, therefore present here a comprehensive characterization of the Halloween genes phantom, disembodied, shadow, shade, spook and spookiest, coding for the P450 enzymes that control the biosynthesis of 20E. Regarding the presence of nuclear receptors in the pea aphid genome, we found 19 genes, representing all of the seven known subfamilies. The annotation and phylogenetic analysis revealed a strong conservation in the class of Insecta. But compared with other sequenced insect genomes, three orthologues are missing in the Acyrthosiphon genome, namely HR96, PNR-like and Knirps. We also cloned the EcR, Usp, E75 and HR3. Finally, 3D-modelling of the ligand-binding domain of Ap-EcR exhibited the typical canonical structural scaffold with 12 alpha-helices associated with a short hairpin of two antiparallel beta-strands. Upon docking, 20E was located in the hormone-binding groove, supporting the hypothesis that EcR has a role in 20E signalling.

Comprehensive survey of developmental genes in the pea aphid, Acyrthosiphon pisum: frequent lineage-specific duplications and losses of developmental genes

Aphids exhibit unique attributes, such as polyphenisms and specialized cells to house endosymbionts, that make them an interesting system for studies at the interface of ecology, evolution and development. Here we present a comprehensive characterization of the developmental genes in the pea aphid, Acyrthosiphon pisum, and compare our results to other sequenced insects. We investigated genes involved in fundamental developmental processes such as establishment of the body plan and organogenesis, focusing on transcription factors and components of signalling pathways. We found that most developmental genes were well conserved in the pea aphid, although many lineage-specific gene duplications and gene losses have occurred in several gene families. In particular, genetic components of transforming growth factor beta (TGFbeta) Wnt, JAK/STAT (Janus kinase/signal transducer and activator of transcription) and EGF (Epidermal Growth Factor) pathways appear to have been significantly modified in the pea aphid.