Cross-kingdom RNA interference mediated by insect salivary microRNAs may suppress plant immunity.

Communication between insects and plants relies on the exchange of bioactive molecules that traverse the species interface. Although proteinic effectors have been extensively studied, our knowledge of other molecules involved in this process remains limited. In this study, we investigate the role of salivary microRNAs (miRNAs) from the rice planthopper Nilaparvata lugens in suppressing plant immunity. A total of three miRNAs were confirmed to be secreted into host plants during insect feeding. Notably, the sequence-conserved miR-7-5P is specifically expressed in the salivary glands of N. lugens and is secreted into saliva, distinguishing it significantly from homologues found in other insects. Silencing miR-7-5P negatively affects N. lugens feeding on rice plants, but not on artificial diets. The impaired feeding performance of miR-7-5P-silenced insects can be rescued by transgenic plants overexpressing miR-7-5P. Through target prediction and experimental testing, we demonstrate that miR-7-5P targets multiple plant genes, including the immune-associated bZIP transcription factor 43 (OsbZIP43). Infestation of rice plants by miR-7-5P-silenced insects leads to the increased expression of OsbZIP43, while the presence of miR-7-5P counteracts this upregulation effect. Furthermore, overexpressing OsbZIP43 confers plant resistance against insects which can be subverted by miR-7-5P. Our findings suggest a mechanism by which herbivorous insects have evolved salivary miRNAs to suppress plant immunity, expanding our understanding of cross-kingdom RNA interference between interacting organisms.

The genomic history and global migration of a windborne pest.

Many insect pests, including the brown planthopper (BPH), undergo windborne migration that is challenging to observe and track. It remains controversial about their migration patterns and largely unknown regarding the underlying genetic basis. By analyzing 360 whole genomes from around the globe, we clarify the genetic sources of worldwide BPHs and illuminate a landscape of BPH migration showing that East Asian populations perform closed-circuit journeys between Indochina and the Far East, while populations of Malay Archipelago and South Asia undergo one-way migration to Indochina. We further find round-trip migration accelerates population differentiation, with highly diverged regions enriching in a gene desert chromosome that is simultaneously the speciation hotspot between BPH and related species. This study not only shows the power of applying genomic approaches to demystify the migration in windborne migrants but also enhances our understanding of how seasonal movements affect speciation and evolution in insects.

A pipeline contributes to efficient identification of salivary proteins in short-headed planthopper, Epeurysa nawaii.

Saliva, an oral secretion primarily originating from salivary glands (SGs), exert critical roles in the ongoing evolutionary interaction between insects and plants. However, identifying insect salivary components poses challenges due to the tiny size of insects, low secretion amounts, and the propensity for degradation after secretion. In this study, we developed a transcriptome-based approach to comprehensively analyze the salivary proteins of the short-headed planthopper, Epeurysa nawaii, a species with unique feeding habits on bamboo. A total of 165 salivary proteins were identified, with 114 secretory genes highly and specifically expressed in SGs. Consistent with most phloem-feeding insects, digestive enzymes, calcium-binding proteins, oxidoreductases, and a few previously reported salivary effectors were ubiquitously distributed in E. nawaii saliva. However, we also identified a substantial portion of salivary proteins exhibiting taxonomy specificity, including 60 E. nawaii-specific and 62 Delphacidae-specific proteins. These taxonomy-restricted proteins potentially play a role in insect adaptation to specific host plants. Our study provides an efficient pipeline for salivary protein identification and serves as a valuable resource for the functional characterization of effectors.

Salivary proteins potentially derived from horizontal gene transfer are critical for salivary sheath formation and other feeding processes.

Herbivorous insects employ an array of salivary proteins to aid feeding. However, the mechanisms behind the recruitment and evolution of these genes to mediate plant-insect interactions remain poorly understood. Here, we report a potential horizontal gene transfer (HGT) event from bacteria to an ancestral bug of Eutrichophora. The acquired genes subsequently underwent duplications and evolved through co-option. We annotated them as horizontal-transferred, Eutrichophora-specific salivary protein (HESPs) according to their origin and function. In Riptortus pedestris (Coreoidea), all nine HESPs are secreted into plants during feeding. The RpHESP4 to RpHESP8 are recently duplicated and found to be indispensable for salivary sheath formation. Silencing of RpHESP4-8 increases the difficulty of R. pedestris in probing the soybean, and the treated insects display a decreased survivability. Although silencing the other RpHESPs does not affect the salivary sheath formation, negative effects are also observed. In Pyrrhocoris apterus (Pyrrhocoroidea), five out of six PaHESPs are secretory salivary proteins, with PaHESP3 being critical for insect survival. The PaHESP5, while important for insects, no longer functions as a salivary protein. Our results provide insight into the potential origin of insect saliva and shed light on the evolution of salivary proteins.

Maintenance of persistent transmission of a plant arbovirus in its insect vector mediated by the Toll-Dorsal immune pathway.

Throughout evolution, arboviruses have developed various strategies to counteract the host's innate immune defenses to maintain persistent transmission. Recent studies have shown that, in addition to bacteria and fungi, the innate Toll-Dorsal immune system also plays an essential role in preventing viral infections in invertebrates. However, whether the classical Toll immune pathway is involved in maintaining the homeostatic process to ensure the persistent and propagative transmission of arboviruses in insect vectors remain unclear. In this study, we revealed that the transcription factor Dorsal is actively involved in the antiviral defense of an insect vector (Laodelphax striatellus) by regulating the target gene, zinc finger protein 708 (LsZN708), which mediates downstream immune-related effectors against infection with the plant virus (Rice stripe virus, RSV). In contrast, an antidefense strategy involving the use of the nonstructural-protein (NS4) to antagonize host antiviral defense through competitive binding to Dorsal from the MSK2 kinase was employed by RSV; this competitive binding inhibited Dorsal phosphorylation and reduced the antiviral response of the host insect. Our study revealed the molecular mechanism through which Toll-Dorsal-ZN708 mediates the maintenance of an arbovirus homeostasis in insect vectors. Specifically, ZN708 is a newly documented zinc finger protein targeted by Dorsal that mediates the downstream antiviral response. This study will contribute to our understanding of the successful transmission and spread of arboviruses in plant or invertebrate hosts.

Comparative transcriptomic analysis of salivary glands between the zoophytophagous Cyrtorhinus lividipennis and the phytozoophagous Apolygus lucorum.

BACKGROUND: Saliva plays a crucial role in shaping the feeding behavior of insects, involving processes such as food digestion and the regulation of interactions between insects and their hosts. Cyrtorhinus lividipennis serves as a predominant natural enemy of rice pests, while Apolygus lucorum, exhibiting phytozoophagous feeding behavior, is a destructive agricultural pest. In this study, a comparative transcriptome analysis, incorporating the published genomes of C.lividipennis and A.lucorum, was conducted to reveal the role of salivary secretion in host adaptation. RESULTS: In contrast to A.lucorum, C.lividipennis is a zoophytophagous insect. A de novo genome analysis of C.lividipennis yielded 19,706 unigenes, including 16,217 annotated ones. On the other hand, A.lucorum had altogether 20,111 annotated genes, as obtained from the published official gene set (20,353 unigenes). Functional analysis of the top 1,000 salivary gland (SG)-abundant genes in both insects revealed that the SG was a dynamically active tissue engaged in protein synthesis and secretion. Predictions of other tissues and signal peptides were compared. As a result, 94 and 157 salivary proteins were identified in C.lividipennis and A.lucorum, respectively, and were categorized into 68 and 81 orthogroups. Among them, 26 orthogroups were shared, potentially playing common roles in digestion and detoxification, including several venom serine proteases. Furthermore, 42 and 55 orthogroups were exclusive in C.lividipennis and A.lucorum, respectively, which were exemplified by a hyaluronidase in C.lividipennis that was associated with predation, while polygalacturonases in A.lucorum were involved in mesophyll-feeding patterns. CONCLUSIONS: Findings in this study provide a comprehensive insight into saliva secretions in C.lividipennis and A.lucorum via a transcriptome approach, reflecting the intricate connections between saliva secretions and feeding behaviors. It is found that conserved salivary secretions are involved in shaping the overlapping feeding patterns, while a plethora of unique salivary secretions may drive the evolution of specific feeding behaviors crucial for their survival. These results enhance our understanding of the feeding mechanisms in different insects from the perspective of saliva and contribute to future environmentally friendly pest control by utilizing predatory insects.

Co-option of a non-retroviral endogenous viral element in planthoppers.

Non-retroviral endogenous viral elements (nrEVEs) are widely dispersed throughout the genomes of eukaryotes. Although nrEVEs are known to be involved in host antiviral immunity, it remains an open question whether they can be domesticated as functional proteins to serve cellular innovations in arthropods. In this study, we found that endogenous toti-like viral elements (ToEVEs) are ubiquitously integrated into the genomes of three planthopper species, with highly variable distributions and polymorphism levels in planthopper populations. Three ToEVEs display exon‒intron structures and active transcription, suggesting that they might have been domesticated by planthoppers. CRISPR/Cas9 experiments revealed that one ToEVE in Nilaparvata lugens, NlToEVE14, has been co-opted by its host and plays essential roles in planthopper development and fecundity. Large-scale analysis of ToEVEs in arthropod genomes indicated that the number of arthropod nrEVEs is currently underestimated and that they may contribute to the functional diversity of arthropod genes.

Horizontally Transferred Salivary Protein Promotes Insect Feeding by Suppressing Ferredoxin-Mediated Plant Defenses.

Herbivorous insects such as whiteflies, planthoppers, and aphids secrete abundant orphan proteins to facilitate feeding. Yet, how these genes are recruited and evolve to mediate plant-insect interaction remains unknown. In this study, we report a horizontal gene transfer (HGT) event from fungi to an ancestor of Aleyrodidae insects approximately 42 to 190 million years ago. BtFTSP1 is a salivary protein that is secreted into host plants during Bemisia tabaci feeding. It targets a defensive ferredoxin 1 in Nicotiana tabacum (NtFD1) and disrupts the NtFD1-NtFD1 interaction in plant cytosol, leading to the degradation of NtFD1 in a ubiquitin-dependent manner. Silencing BtFTSP1 has negative effects on B. tabaci feeding while overexpressing BtFTSP1 in N. tabacum benefits insects and rescues the adverse effect caused by NtFD1 overexpression. The association between BtFTSP1 and NtFD1 is newly evolved after HGT, with the homologous FTSP in its fungal donor failing to interact and destabilize NtFD1. Our study illustrates the important roles of horizontally transferred genes in plant-insect interactions and suggests the potential origin of orphan salivary genes.

Comparative Transcriptomic Analysis Reveals Adaptation Mechanisms of Bean Bug Riptortus pedestris to Different Food Resources.

The bean bug, Riptortus pedestris (Hemiptera: Heteroptera), poses a significant threat to soybean production, resulting in substantial crop losses. Throughout the soybean cultivation period, these insects probe and suck on various parts of plants, including leaves, pods, and beans. However, the specific mechanisms by which they adapt to different food resources remain unknown. In this study, we conducted gut transcriptomic analyses of R. pedestris fed with soybean leaves, pods, and beans. A total of 798, 690, and 548 differently expressed genes (DEGs) were monitored in G-pod vs. G-leaf (comparison of insect feeding on pods and leaves), G-bean vs. G-leaf (comparison of insect feeding on beans and leaves), and G-pod vs. G-bean (comparison of insect feeding on pods and beans), respectively. When fed on pods and beans, there was a significant increase in the expression of digestive enzymes, particularly cathepsins, serine proteases, and lipases. Conversely, when soybean leaves were consumed, detoxification enzymes, such as ABC transporters and 4-coumarate-CoA ligase, exhibited higher expression. Our findings indicate that R. pedestris dynamically regulates different metabolic pathways to cope with varying food resources, which may contribute to the development of effective strategies for managing this pest.

Transcriptomic Analysis of Tobacco Plants in Response to Whitefly Infection.

The whitefly Bemisia tabaci is one of the most destructive pests worldwide, and causes tremendous economic losses. Tobacco Nicotiana tabacum serves as a model organism for studying fundamental biological processes and is severely damaged by whiteflies. Hitherto, our knowledge of how tobacco perceives and defends itself against whiteflies has been scare. In this study, we analyze the gene expression patterns of tobacco in response to whitefly infestation. A total of 244 and 2417 differentially expressed genes (DEGs) were identified at 12 h and 24 h post whitefly infestation, respectively. Enrichment analysis demonstrates that whitefly infestation activates plant defense at both time points, with genes involved in plant pattern recognition, transcription factors, and hormonal regulation significantly upregulated. Notably, defense genes are more intensely upregulated at 24 h post infestation than at 12 h, indicating an increased immunity induced by whitefly infestation. In contrast, genes associated with energy metabolism, carbohydrate metabolism, ribosomes, and photosynthesis are suppressed, suggesting impaired plant development. Taken together, our study provides comprehensive insights into how plants respond to phloem-feeding insects, and offers a theoretical basis for better research on plant-insect interactions.

Insight into phenotypic plasticity in planthoppers.

Planthoppers possess an impressive ability to exhibit phenotypic plasticity, which allows them to adjust their morphology for migration, overwintering, and adaptation to different environmental conditions. The wing and color polyphenism are the two most outward morphologies. Wing polyphenism serves as a classic illustration of a life history trade-off between reproduction and migration, while color polyphenism is potentially correlated with the insect development and immunity. In this review, we present the important contributions that link environment cues to wing and color polyphenism, and highlight recent advances in insulin/insulin-like growth factor signaling-forkhead transcription factor subgroup O (FoxO) pathway-mediated wing development and tyrosine-melanin pathway-mediated coloration. Further work, particularly in the identification of the genes that FoxO regulates and in the elucidation of the intracellular signals that link the stimuli to the tyrosine-melanin pathway, is required.

Functional analysis of neutral lipases in bug feeding and reproduction.

BACKGROUND: The bean bug, Riptortus pedestris, is known to cause significant economic losses in soybean crops due to its seed-sucking behavior, but the mechanism of its adaptation to lipid-rich seeds remains poorly understood. To exploit potential target genes for controlling this pest, neutral lipases are functionally characterized in this study. RESULTS: In this study, a total of 69 lipases were identified in R. pedestris, including 35 neutral lipases that underwent significant expansion. The phylogeny, expression patterns, and catalytic capacity of neutral lipases were investigated and we selected six salivary gland-specific, eight gut-specific, and three ovary-specific genes for functional analysis. All three ovary-specific neutral lipases (Chr1.3195, Chr1.0994, and Chr5.0087) are critical for insect reproduction, while a few gut-specific neutral lipases (Chr4.0221 and Chr1.3207) influence insect survivorship or weight gain. In contrast, no significant phenotype change is observed when silencing salivary gland-specific neutral lipases. CONCLUSION: The lipases Chr1.3195, Chr1.0994, Chr5.0087, Chr4.0221, and Chr1.3207 are essential for R. pedestris feeding and reproduction, and the insect is highly sensitive to their deficiency, suggesting that neutral lipases are promising candidates for application in RNAi-based control of this destructive pest. © 2023 Society of Chemical Industry.

Case Report: A tortuous diagnosis and successful multimodal treatment of thyroid follicular carcinoma with pelvic metastasis.

Purpose: To provide reference method for the treatment of thyroid follicular carcinoma by studing the clinical imaging, pathological features and multimodal treatment of a case of thyroid follicular carcinoma with bone metastasis. Methods: By identifying the case's clinical, imaging, pathological features of a case of thyroid follicular carcinoma with bone metastasis, reflecting on the case's diagnosis and treatment process, and referring to literature about the characteristics of thyroid follicular carcinoma, the study aims to provide reference for the treatment of this kind of disease. Result: A 67-year-old male patient was admitted to the hospital with clinical symptoms of left pelvic pain. The biopsy pathology showed well-differentiated thyroid tissue. Considering his medical history, conclusion of thyroid follicular carcinoma metastasis could be made.The patient was stable and no tumor progression was observed after a combination of therapies including 131I and topical and targeted agents. Conclusions: Thyroid follicular carcinoma are prone to bone metastasis, and bone metastasis is the first symptom in some cases. Clinical imaging and pathology are needed for correct diagnosis, and a successful treatment requires a combination of multiple approaches including 131I, which is a Radioactive Iodine Therapy(RAI), local therapy and targeted drug therapy.

Long-wave opsin involved in body color plastic development in Nilaparvata lugens.

BACKGROUND: As one of the components of visual photopigments in photoreceptor cells, opsin exhibits different spectral peaks and plays crucial roles in visual function. Besides, it is discovered to evolve other functions despite color vision. However, research on its unconventional function is limited nowadays. With the increase in genome database numbers, various numbers and types of opsins have been identified in insects due to gene duplications or losses. The Nilaparvata lugens (Hemiptera) is a rice pest known for its long-distance migration capability. In this study, opsins were identified in N. lugens and characterized by genome and transcriptome analyses. Meanwhile, RNA interference (RNAi) was carried out to investigate the functions of opsins, and then the Illumina Novaseq 6000 platform-based transcriptome sequencing was performed to reveal gene expression patterns. RESULTS: Four opsins belonging to G protein-coupled receptors were identified in the N. lugens genome, including one long-sensitive opsin (Nllw) together with two ultraviolet-sensitive opsins (NlUV1/2) and an additional new opsin with hypothesized UV peak sensitivity (NlUV3-like). A tandem array of NlUV1/2 on the chromosome suggested the presence of a gene duplication event, with similar exons distribution. Moreover, as revealed by spatiotemporal expression, the four opsins were highly expressed in eyes with age-different expression levels. Besides, RNAi targeting each of the four opsins did not significantly affect the survival of N. lugens in phytotron, but the silencing of Nllw resulted in the melanization of body color. Further transcriptome analysis revealed that silencing of Nllw resulted in up-regulation of a tyrosine hydroxylase gene (NlTH) and down-regulation of an arylalkylamine-N-acetyltransferases gene (NlaaNAT) in N. lugens, demonstrating that Nllw is involved in body color plastic development via the tyrosine-mediated melanism pathway. CONCLUSIONS: This study provides the first evidence in a Hemipteran insect that an opsin (Nllw) takes part in the regulation of cuticle melanization, confirming a cross-talk between the gene pathways underlying the visual system and the morphological differentiation in insects.

The JAK-STAT pathway promotes persistent viral infection by activating apoptosis in insect vectors.

The Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway is an evolutionarily conserved signaling pathway that can regulate various biological processes. However, the role of JAK-STAT pathway in the persistent viral infection in insect vectors has rarely been investigated. Here, using a system that comprised two different plant viruses, Rice stripe virus (RSV) and Rice black-streaked dwarf virus (RBSDV), as well as their insect vector small brown planthopper, we elucidated the regulatory mechanism of JAK-STAT pathway in persistent viral infection. Both RSV and RBSDV infection activated the JAK-STAT pathway and promoted the accumulation of suppressor of cytokine signaling 5 (SOCS5), an E3 ubiquitin ligase regulated by the transcription factor STAT5B. Interestingly, the virus-induced SOCS5 directly interacted with the anti-apoptotic B-cell lymphoma-2 (BCL2) to accelerate the BCL2 degradation through the 26S proteasome pathway. As a result, the activation of apoptosis facilitated persistent viral infection in their vector. Furthermore, STAT5B activation promoted virus amplification, whereas STAT5B suppression inhibited apoptosis and reduced virus accumulation. In summary, our results reveal that virus-induced JAK-STAT pathway regulates apoptosis to promote viral infection, and uncover a new regulatory mechanism of the JAK-STAT pathway in the persistent plant virus transmission by arthropod vectors.

Planthopper salivary sheath protein LsSP1 contributes to manipulation of rice plant defenses.

Salivary elicitors secreted by herbivorous insects can be perceived by host plants to trigger plant immunity. However, how insects secrete other salivary components to subsequently attenuate the elicitor-induced plant immunity remains poorly understood. Here, we study the small brown planthopper, Laodelphax striatellus salivary sheath protein LsSP1. Using Y2H, BiFC and LUC assays, we show that LsSP1 is secreted into host plants and binds to salivary sheath via mucin-like protein (LsMLP). Rice plants pre-infested with dsLsSP1-treated L. striatellus are less attractive to L. striatellus nymphs than those pre-infected with dsGFP-treated controls. Transgenic rice plants with LsSP1 overexpression rescue the insect feeding defects caused by a deficiency of LsSP1 secretion, consistent with the potential role of LsSP1 in manipulating plant defenses. Our results illustrate the importance of salivary sheath proteins in mediating the interactions between plants and herbivorous insects.

Chromosome-level Assembly, Dosage Compensation and Sex-biased Gene Expression in the Small Brown Planthopper, Laodelphax striatellus.

In insects, sex chromosome differentiation often results in unequal gene dosages between sexes. Dosage compensation mechanisms evolve to balance gene expression, but the degree and mechanism of regulation often vary by insect species. In hemipteran species, the small brown planthopper (SBPH), Laodelphax striatellus, is an injurious crop pest, with a sex chromosome type XX in females and XO in males. This species offers the opportunity to study dosage compensation and sex-biased gene expression. In this study, we generated a chromosome-level genome of SBPH using Oxford Nanopore Technologies and high-throughput chromatin conformation capture (Hi-C) technology. We also sequenced RNA-seq data from 16 tissue samples to annotate the genome and analyze gene dosage compensation. We finally obtained a 510.2 megabases (Mb) genome with 99.12% of the scaffolds anchored on 15 chromosomes (14 autosomes and 1 X chromosome) and annotated 16,160 protein-coding genes based on full-length cDNA sequencing data. Furthermore, we found complete dosage compensation in all L. striatellus somatic tissues, but lack of dosage compensation in gonad tissue testis. We also found that female-biased genes were significantly enriched on the X chromosome in all tissues, whereas male-biased genes in gonad tissues were enriched on autosomes. This study not only provides a high-quality genome assembly but also lays a foundation for a better understanding of the sexual regulatory network in hemipteran insects.

Complete genome analysis of a novel iflavirus from the spotted lanternfly Lycorma delicatula.

The spotted lanternfly (Lycorma delicatula) is an invasive pest that causes serious economic losses in fruit and wood production. Here, we identified a novel iflavirus named "Lycorma delicatula iflavirus 1" (LDIV1), in a spotted lanternfly. The full genome sequence of LDIV1 is 10,222 nt in length and encodes a polyprotein containing a picornavirus capsid-protein-domain-like domain, a cricket paralysis virus capsid superfamily domain, an RNA helicase domain, a peptidase C3 superfamily domain, and an RNA-dependent RNA polymerase (RdRp) domain. LDIV1 replicates in the host insect and activates small interfering RNA (siRNA)-based host antiviral immunity. Phylogenetic analysis demonstrated that LDIV1 is most closely related to an unspecified member of the order Picornavirales, with 61.7% sequence identity in the RdRp region and 57.6% sequence identity in the coat protein region, and thus meets the demarcation criteria for new species in the genus Iflavirus. To the best of our knowledge, LDIV1 is the first virus discovered in L. delicatula.

Characterization of Two Novel Insect-Specific Viruses Discovered in the Green Leafhopper, Cicadella viridis.

Insect-specific viruses (ISV) are one of the most promising agents for the biological control of insects. The green leafhopper, Cicadella viridis (Linnaeus), is an significant pest in agriculture, and causes economic losses to fruit trees, willows, and field crops. As a representative species of the large family Cicadellidae, ISVs in C. viridis have never been studied, to date. In this study, the full genome sequences of two ISVs, named Cicadella viridis iflavirus1 (CvIfV1), and Cicadella viridis nido-like virus 1 (CvNiLV1), were revealed using a metatranscriptomic approach. A homology search and phylogenetic analysis indicated that CvIfV1 is a new member in the family Iflaviridae (genus Iflavirus) with a typical iflavirus genome organization, whereas CvNiLV1 belongs to the unclassified clade/family of the order Nidovirales. In addition, analysis of virus-derived small interfering RNAs (vsiRNAs) was performed to investigate the antiviral RNA interference (RNAi) response of C. viridis. The vsiRNAs exhibit typical patterns produced by host siRNA-mediated antiviral immunity, including a preference of 21-nt vsiRNAs derived equally from the sense and antisense genomic strands, and a strong A/U bias in the 5'-terminus of the viral genomes. Our study provides valuable information for ISVs in leafhoppers for the first time, which might prove useful in the control of C. viridis in future.