Glutamate-GABA imbalance mediated by miR-8-5p and its STTM regulates phase-related behavior of locusts.

The aggregation of locusts from solitary to gregarious phases is crucial for the formation of devastating locust plagues. Locust management requires research on the prevention of aggregation or alternative and greener solutions to replace insecticide use, and insect-derived microRNAs (miRNAs) show the potential for application in pest control. Here, we performed a genome-wide screen of the differential expression of miRNAs between solitary and gregarious locusts and showed that miR-8-5p controls the γ-aminobutyric acid (GABA)/glutamate functional balance by directly targeting glutamate decarboxylase (Gad). Blocking glutamate-GABA neurotransmission by miR-8-5p overexpression or Gad RNAi in solitary locusts decreased GABA production, resulting in locust aggregation behavior. Conversely, activating this pathway by miR-8-5p knockdown in gregarious locusts induced GABA production to eliminate aggregation behavior. Further results demonstrated that ionotropic glutamate/GABA receptors tuned glutamate/GABA to trigger/hamper the aggregation behavior of locusts. Finally, we successfully established a transgenic rice line expressing the miR-8-5p inhibitor by short tandem target mimic (STTM). When locusts fed on transgenic rice plants, Gad transcript levels in the brain increased greatly, and aggregation behavior was lost. This study provided insights into different regulatory pathways in the phase change of locusts and a potential control approach through behavioral regulation in insect pests.

Non-canonical function of an Hif-1α splice variant contributes to the sustained flight of locusts.

The hypoxia inducible factor (Hif) pathway is functionally conserved across metazoans in modulating cellular adaptations to hypoxia. However, the functions of this pathway under aerobic physiological conditions are rarely investigated. Here, we show that Hif-1α2, a locust Hif-1α isoform, does not induce canonical hypoxic responses but functions as a specific regulator of locust flight, which is a completely aerobic physiological process. Two Hif-1α splice variants were identified in locusts, a ubiquitously expressed Hif-1α1 and a muscle-predominantly expressed Hif-1α2. Hif-1α1 that induces typical hypoxic responses upon hypoxia exposure remains inactive during flight. By contrast, the expression of Hif-1α2, which lacks C-terminal transactivation domain, is less sensitive to oxygen tension but induced extensively by flying. Hif-1α2 regulates physiological processes involved in glucose metabolism and antioxidation during flight and sustains flight endurance by maintaining redox homeostasis through upregulating the production of a reactive oxygen species (ROS) quencher, DJ-1. Overall, this study reveals a novel Hif-mediated mechanism underlying prolonged aerobic physiological activity.

Neuroendocrinal and molecular basis of flight performance in locusts.

Insect flight is a complex physiological process that involves sensory and neuroendocrinal control, efficient energy metabolism, rhythmic muscle contraction, and coordinated wing movement. As a classical study model for insect flight, locusts have attracted much attention from physiologists, behaviorists, and neuroendocrinologists over the past decades. In earlier research, scientists made extensive efforts to explore the hormone regulation of metabolism related to locust flight; however, this work was hindered by the absence of molecular and genetic tools. Recently, the rapid development of molecular and genetic tools as well as multi-omics has greatly advanced our understanding of the metabolic, molecular, and neuroendocrinal basis of long-term flight in locusts. Novel neural and molecular factors modulating locust flight and their regulatory mechanisms have been explored. Moreover, the molecular mechanisms underlying phase-dependent differences in locust flight have also been revealed. Here, we provide a systematic review of locust flight physiology, with emphasis on recent advances in the neuroendocrinal, genetic, and molecular basis. Future research directions and potential challenges are also addressed.

Locust density shapes energy metabolism and oxidative stress resulting in divergence of flight traits.

Flight ability is essential for the enormous diversity and evolutionary success of insects. The migratory locusts exhibit flight capacity plasticity in gregarious and solitary individuals closely linked with different density experiences. However, the differential mechanisms underlying flight traits of locusts are largely unexplored. Here, we investigated the variation of flight capacity by using behavioral, physiological, and multiomics approaches. Behavioral assays showed that solitary locusts possess high initial flight speeds and short-term flight, whereas gregarious locusts can fly for a longer distance at a relatively lower speed. Metabolome-transcriptome analysis revealed that solitary locusts have more active flight muscle energy metabolism than gregarious locusts, whereas gregarious locusts show less evidence of reactive oxygen species production during flight. The repression of metabolic activity by RNA interference markedly reduced the initial flight speed of solitary locusts. Elevating the oxidative stress by paraquat injection remarkably inhibited the long-distance flight of gregarious locusts. In respective crowding and isolation treatments, energy metabolic profiles and flight traits of solitary and gregarious locusts were reversed, indicating that the differentiation of flight capacity depended on density and can be reshaped rapidly. The density-dependent flight traits of locusts were attributed to the plasticity of energy metabolism and degree of oxidative stress production but not energy storage. The findings provided insights into the mechanism underlying the trade-off between velocity and sustainability in animal locomotion and movement.

Long Non-coding RNA Derived from lncRNA-mRNA Co-expression Networks Modulates the Locust Phase Change.

Long non-coding RNAs (lncRNAs) regulate various biological processes ranging from gene expression to animal behavior. Although protein-coding genes, microRNAs, and neuropeptides play important roles in the regulation of phenotypic plasticity in migratory locust, empirical studies on the function of lncRNAs in this process remain limited. Here, we applied high-throughput RNA-seq to compare the expression patterns of lncRNAs and mRNAs in the time course of locust phase change. We found that lncRNAs responded more rapidly at the early stages of phase transition. Functional annotations demonstrated that early changed lncRNAs employed different pathways in isolation and crowding phases to cope with changes in the population density. Two overlapping hub lncRNA loci in the crowding and isolation networks were screened for functional verification. One of them, LNC1010057, was validated as a potential regulator of locust phase change. This work offers insights into the molecular mechanism underlying locust phase change and expands the scope of lncRNA functions in animal behavior.

Dop1 enhances conspecific olfactory attraction by inhibiting miR-9a maturation in locusts.

Dopamine receptor 1 (Dop1) mediates locust attraction behaviors, however, the mechanism by which Dop1 modulates this process remains unknown to date. Here, we identify differentially expressed small RNAs associated with locust olfactory attraction after activating and inhibiting Dop1. Small RNA transcriptome analysis and qPCR validation reveal that Dop1 activation and inhibition downregulates and upregulates microRNA-9a (miR-9a) expression, respectively. miR-9a knockdown in solitarious locusts increases their attraction to gregarious volatiles, whereas miR-9a overexpression in gregarious locusts reduces olfactory attraction. Moreover, miR-9a directly targets adenylyl cyclase 2 (ac2), causing its downregulation at the mRNA and protein levels. ac2 responds to Dop1 and mediates locust olfactory attraction. Mechanistically, Dop1 inhibits miR-9a expression through inducing the dissociation of La protein from pre-miR-9a and resulting in miR-9a maturation inhibition. Our results reveal a Dop1-miR-9a-AC2 circuit that modulates locust olfactory attraction underlying aggregation. This study suggests that miRNAs act as key messengers in the GPCR signaling.

The complete mitochondrial genome of the predatory bug Orius sauteri (Poppius) (Hemiptera: Anthocoridae).

The complete mitochondrial genome of the predatory bug Orius sauteri (Poppius) (Hemiptera: Anthocoridae) was sequenced and analyzed (GenBank accession No. KJ671626). The length of this mitochondrial genome is 16,246 bp with 37 typical animal mitochondrial genes; i.e., 13 protein-coding, 2 rRNA and 22 tRNA genes, and an A+T-rich region. The gene arrangement is identical to that of the pupative ancestral arrangement of insects. All protein-coding genes start with ATN start codon, i.e. five ATAs, four ATTs, three ATGs and one ATC. Ten protein-coding genes stop with termination codon TAA. Three protein-coding genes use incomplete stop codon TA. The A+T-rich region are located between rrnS and trnM with a length of 1758 bp and an A+T content of 73.49%.

Rearrangement of trnQ-trnM in the mitochondrial genome of Allantus luctifer (Smith) (Hymenoptera: Tenthredinidae).

The complete mitochondrial genome of the Allantus luctifer (Smith) (Hymenoptera: Tenthredinidae: Allantinae) is reported in this study (GenBank accession No. KJ713152). This is the first mitochondrial genome from the subfamily Allantinae and the first completely sequenced mitochondrial genome from the Tenthredinoidea. The length of this mitochondrial genome is 15,418 bp with an A+T content of 81.13%, including 13 protein-coding, 2 rRNA and 22 tRNA gene, and an A+T-rich region (Table 1). Gene arrangement is identical to the other two mitochondrial genomes of tenthredinoid species in nearly all region as in the pupative ancestral arrangement of insects. The ancestral pattern of "A+T-rich region-trnI(+)-trnQ(-)-trnM(+)" was rearranged to "trnM(-)-trnQ(+)-A+T-rich region-trnI(+)", which is novel to the Hymenoptera. All protein-coding genes start with ATN start codon. Eleven protein-coding genes stop with termination codon TAA, whereas one protein-coding gene uses incomplete stop codon TA and one uses T. The A+T-region is 463 bp long with an A+T content of 86.6%.

The complete mitogenome of the turnip moth Agrotis segetum (Lepidoptera: Noctuidae).

Abstract The complete mitochondrial genome (mitogenome) of the turnip moth Agrotis segetum (Lepidoptera: Noctuidae) was determined (GenBank accession No. KC894725). This is the first sequenced mitogenome from the subfamily Noctuinae of Noctuidae. The length of this mitogenome is 15,378 bp with a A+T content of 80.7%. There are 37 typical animal mitochondrial genes and a A+T-rich region. The tRNA gene trnM was the only rearranged gene compared with the pupative ancestral arrangement of insects. All protein-coding genes start with ATN start codon except for the gene cox1, which uses CGA as in other lepidopteran species. Ten protein-coding genes stop with termination codon TAA, whereas three protein-coding gene use incomplete stop codon T. The A+T-region is located between rrnS and trnM with a length of 332 bp and A+T content of 93.5%.