Progress in the characterization of insulin-like peptides in aphids: Immunohistochemical mapping of ILP4

Isolation of Macrolactin A from a new Bacillus amyloliquefaciens and its aphicidal activity against Rhopalosiphum padi

BACKGROUND

Rhopalosiphum padi is a major infection affecting cereal crops in the boundary area. However, continuous use of chemical pesticides has increased cases of drug resistance in its field population. Therefore, we aimed to verify the insecticidal properties of Bacillus amyloliquefaciens YJNbs21.10 against aphids, isolated to determine the bioactivity of its metabolite Macrolactin A against aphids for the first time.

RESULTS

The results of activity tracking showed that the fermentation broth of YJNbs21.10 had the best inhibitory efficacy against R. padi, and the corrected efficiency reached 95.57% after 24 h. With the continuous separation and test, the efficiency of the active components decreased: Macrolactin A, as the most active substance, had a control activity against aphids under 500 mg L-1 of 74.64% at 72 h, (which was significantly lower than that of fermentation broth, indicating a synergistic effect between the active substances of each part of the strain. In addition, the result of the stereomicroscope showed that Macrolactin A damaged the body wall of aphids. The toxicity of Macrolactin A to R. padi was confirmed through the gradient test.

CONCLUSION

In this study, Bacillus amyloliquefaciens YJNbs21.10 exhibited comparable inhibitory ability to chemical pesticides suggesting its potential to provide effective biological control on aphids. The biological activity of Macrolactin A against aphids was also verified for the first time, in this experiment, the EC50 of this substance against aphids was 169.02 mg L-1 (24 h), which provided strong evidence that YJNbs21.10 may act as an effective agent for the prevention of aphid. © 2024 Society of Chemical Industry.

The circadian and photoperiodic clock of the pea aphid

The pea aphid, Acyrthosiphon pisum, is a paradigmatic photoperiodic species that exhibits a remarkable annual life cycle, which is tightly coupled to the seasonal changes in day length. During spring and summer, characterised by longer days, aphid populations consist exclusively of viviparous females that reproduce parthenogenetically. When autumn comes and the days shorten, aphids switch their reproductive mode and generate males and oviparous sexual females, which mate and produce cold-resistant eggs that overwinter and survive the unfavourable season. While the photoperiodic responses have been well described, the nature of the timing mechanisms which underlie day length discrimination are still not completely understood. Experiments from the 1960's suggested that aphids rely on an 'hourglass' clock measuring the elapsed time during the dark night by accumulating a biochemical factor, which reaches a critical threshold at a certain night length and triggers the switch in reproduction mode. However, the photoperiodic responses of aphids can also be attributed to a strongly dampened circadian clock. Recent studies have uncovered the molecular components and the location of the circadian clock in the brain of the pea aphid and revealed that it is well connected to the neurohormonal system controlling aphid reproduction. We provide an overview of the putative mechanisms of photoperiodic control in aphids, from the photoreceptors involved in this process to the circadian clock and the neuroendocrine system.

A clock for all seasons

Circadian clocks play an essential role in adapting locomotor activity as well as physiological, and metabolic rhythms of organisms to the day-night cycles on Earth during the four seasons. In addition, they can serve as a time reference for measuring day length and adapt organisms in advance to annual changes in the environment, which can be particularly pronounced at higher latitudes. The physiological responses of organisms to day length are also known as photoperiodism. This special issue of the Journal of Comparative Physiology A aims to account for diurnal and photoperiodic adaptations by presenting a collection of ten review articles, five original research articles, and three perspective pieces. The contributions include historical accounts, circadian and photoperiodic clock models, epigenetic, molecular, and neuronal mechanisms of seasonal adaptations, latitudinal differences in photoperiodic responses and studies in the wild that address the challenges of global change.

Two distinct aphid diapause strategies: slow development or development arrest

Aphids adapt to unfavourable environmental conditions, such as low temperatures in winter, by laying diapausing eggs that overwinter. Diapause is a stress-resistant and developmentally arrested stage that can be adopted in order to increase the chance of survival in adverse environmental conditions. The diapause process of aphids is still very poorly understood. We followed the development of two species of aphids, Brachycorynella asparagi and Appendiseta robiniae, using the immunostained embryos of the aphids to identify mitotic cell divisions. Two different models of aphid diapause were demonstrated for the first time. In the first strategy, the embryo developed continuously during winter diapause, while in the second case, there was an embryonic arrest. The possibility of slow development of the whole body during diapause is a characteristic feature of aphids. The link to the plant's phenology appears to be a key factor in determining the diapause strategy in aphids.

Variation of insulin-related peptides accompanying the differentiation of Aphis gossypii biotypes and their expression profiles

Insulin signaling plays a critical role in regulating various aspects of insect biology, including development, reproduction, and the formation of wing polyphenism. This leads to differentiation among insect populations at different levels. The insulin family exhibits functional variation, resulting in diverse functional pathways. Aphis gossypii Glover, commonly known as the cotton-melon aphid, is a highly adaptable aphid species that has evolved into multiple biotypes. To understand the genetic structure of the insulin family and its evolutionary diversification and expression patterns in A. gossypii, we conducted studies using genome annotation files and RNA-sequencing data. Consequently, we identified 11 insulin receptor protein (IRP) genes in the genomes of the examined biotypes. Among these, eight AgosIRPs were dispersed across the X chromosome, while two were found in tandem on the A1 chromosome. Notably, AgosIRP2 exhibited alternative splicing, resulting in the formation of two isoforms. The AgosIRP genes displayed a high degree of conservation between Hap1 and Hap3, although some variations were observed between their genomes. For instance, a transposon was present in the coding regions of AgosIRP3 and AgosIRP9 in the Hap3 genome but not in the Hap1 genome. RNA-sequencing data revealed that four AgosIRPs were expressed ubiquitously across different morphs of A. gossypii, while others showed specific expression patterns in adult gynopara and adult males. Furthermore, the expression levels of most AgosIRPs decreased upon treatment with the pesticide acetamiprid. These findings demonstrate the evolutionary diversification of AgosIRPs between the genomes of the two biotypes and provide insights into their expression profiles across different morphs, developmental stages, and biotypes. Overall, this study contributes valuable information for investigating aphid genome evolution and the functions of insulin receptor proteins.

Pigment-dispersing factor is present in circadian clock neurons of pea aphids and may mediate photoperiodic signalling to insulin-producing cells

The neuropeptide pigment-dispersing factor (PDF) plays a pivotal role in the circadian clock of most Ecdysozoa and is additionally involved in the timing of seasonal responses of several photoperiodic species. The pea aphid, Acyrthosiphon pisum, is a paradigmatic photoperiodic species with an annual life cycle tightly coupled to the seasonal changes in day length. Nevertheless, PDF could not be identified in A. pisum so far. In the present study, we identified a PDF-coding gene that has undergone significant changes in the otherwise highly conserved insect C-terminal amino acid sequence. A newly generated aphid-specific PDF antibody stained four neurons in each hemisphere of the aphid brain that co-express the clock protein Period and have projections to the pars lateralis that are highly plastic and change their appearance in a daily and seasonal manner, resembling those of the fruit fly PDF neurons. Most intriguingly, the PDF terminals overlap with dendrites of the insulin-like peptide (ILP) positive neurosecretory cells in the pars intercerebralis and with putative terminals of Cryptochrome (CRY) positive clock neurons. Since ILP has been previously shown to be crucial for seasonal adaptations and CRY might serve as a circadian photoreceptor vital for measuring day length, our results suggest that PDF plays a critical role in aphid seasonal timing.

Differential expression of some termite neuropeptides and insulin/IGF-related hormones and their plausible functions in growth, reproduction and caste determination

Background

Insulin-like growth factor (IGF) and other insulin-like peptides (ilps) are important hormones regulating growth and development in animals. Whereas most animals have a single female and male adult phenotype, in some insect species the same genome may lead to different final forms. Perhaps the best known example is the honeybee where females can either develop into queens or workers. More extreme forms of such polyphenism occur in termites, where queens, kings, workers and soldiers coexist. Both juvenile hormone and insulin-like peptides are known to regulate growth and reproduction as well as polyphenism. In termites the role of juvenile hormone in reproduction and the induction of the soldier caste is well known, but the role of IGF and other ilps in these processes remains largely unknown. Here the various termite ilps are identified and hypotheses regarding their functions suggested.

Methods

Genome assemblies and transcriptome short read archives (SRAs) were used to identify insulin-like peptides and neuropeptides in termites and to determine their expression in different species, tissues and castes.

Results and Discussion

Termites have seven different ilps, i.e. gonadulin, IGF and an ortholog of Drosophila insulin-like peptide 7 (dilp7), which are commonly present in insects, and four smaller peptides, that have collectively been called short IGF-related peptides (sirps) and individually atirpin, birpin, cirpin and brovirpin. Gonadulin is lost from the higher termites which have however amplified the brovirpin gene, of which they often have two or three paralogs. Based on differential expression of these genes it seems likely that IGF is a growth hormone and atirpin an autocrine tissue factor that is released when a tissue faces metabolic stress. Birpin seems to be responsible for growth and in the absence of juvenile hormone this may lead to reproductive adults or, when juvenile hormone is present, to soldiers. Brovirpin is expressed both by the brain and the ovary and likely stimulates vitellogenesis, while the function of cirpin is less clear.

Mapping and quantification of cryptochrome expression in the brain of the pea aphid Acyrthosiphon pisum

Aphids are paradigmatic photoperiodic animals often used to study the role of the circadian clock in the seasonal response. Previously, we described some elements of the circadian clock core (genes period and timeless) and output (melatonin, AANATs and PTTH) that could have a role in the regulation of the aphid seasonal response. More recently, we identified two opsins (C-ops and SWO4) as candidate input photoperiodic receptors. In the present report, we focus on the study of cryptochromes (cry) as photoreceptors of the circadian clock and discuss their involvement in the seasonal response. We analyse the expression of cry1 and cry2 genes in a circadian and seasonal context, and map their expression sites in the brain. We observe a robust rhythmic expression of cry2 peaking at dusk in phase with core clock genes period and timeless, while cry1 shows a weaker rhythm. Changes in cry1 and cry2 expression correlate with activation of the seasonal response, suggesting a possible link. Finally, we map the expression of cry1 and cry2 genes to clock neurons in the pars lateralis, a region essential for the photoperiodic response. Our results support a role for cry as elements of the aphid circadian clock and suggest a role in photoreception for cry1 and in clock repression for cry2.