Constructing the major biosynthesis pathways for amino acids in the brown planthopper, Nilaparvata lugens Stål (Hemiptera: Delphacidae), based on the transcriptome data

Establishment of a Rapid Detection Method for Yeast-like Symbionts in Brown Planthopper Based on Droplet Digital PCR Technology

The brown planthopper Nilaparvata lugens (Stål) (BPH) is a typical monophagous sucking rice pest. Over the course of their evolution, BPH and its symbionts have established an interdependent and mutually beneficial relationship, with the symbionts being important to the growth, development, reproduction, and variation in virulence of BPH. Yeast-like symbionts (YLS), harbored in the abdomen fat body cells of BPH, are vital to the growth and reproduction of the host. In recent research, the symbionts in BPH have mainly been detected using blood cell counting, PCR, real-time quantitative PCR, and other methods. These methods are vulnerable to external interference, cumbersome, time consuming and laborious. Droplet digital PCR (ddPCR) does not need a standard curve, can achieve absolute quantification, does not rely on Cq values, and is more useful for analyzing copy number variation, gene mutations, and relative gene expression. A rapid detection method for the YLS of BPH based on ddPCR was established and optimized in this study. The results showed that the method's limits of detection for the two species of YLS (Ascomycetes symbionts and Pichia guilliermondii) were 1.3 copies/μL and 1.2 copies/μL, respectively. The coefficient of variation of the sample repetition was less than 5%; therefore, the ddPCR method established in this study had good sensitivity, specificity, and repeatability. It can be used to detect the YLS of BPH rapidly and accurately.

TM7 (Saccharibacteria) regulates the synthesis of linolelaidic acid and tricosanoic acid, and alters the key metabolites in diapause Clanis bilineata tsingtauica

Good exploitation and utilization of edible insects can effectively alleviate global food security crisis in years. The study on diapause larvae of Clanis bilineata tsingtauica (DLC) was conducted to explore how gut microbiota regulate the nutrients synthesis and metabolism of edible insects. The results showed that C. bilineata tsingtauica maintained a total and stable nutrition levels at early phase of diapause. The activity of instetinal enzymes in DLC fluctuated markedly with diapause time. Additionally, Proteobacteria and Firmicutes were the predominant taxa, and TM7 (Saccharibacteria) was the marker species of gut microbiota in DLC. Combined the gene function prediction analysis with Pearson correlation analysis, TM7 in DLC was mainly involved in the biosynthesis of diapause-induced differential fatty acids, i.e., linolelaidic acid (LA) and tricosanoic acid (TA), which was probably regulated by changing the activity of protease and trehalase, respectively. Moreover, according to the non-target metabolomics, TM7 might regulate the significant differential metabolites, i.e., D-glutamine, N-acetyl-d-glucosamine and trehalose, via the metabolism of amino acid and carbohydrate pathways. These results suggest that TM7 increased LA and decreased TA via the intestinal enzymes, and altered intestinal metabolites via the metabolism pathways, maybe a key mechanism for regulating the nutrients synthesis and metabolisms in DLC.

Community Dynamics in Structure and Function of Honey Bee Gut Bacteria in Response to Winter Dietary Shift

Temperate honey bees (Apis mellifera) are challenged by low temperatures and abrupt dietary shifts associated with behavioral changes during winter. Case studies have revealed drastic turnover in the gut microbiota of winter bees, highlighted by the seasonal dominance of a non-core bacterium Bartonella. However, neither biological consequence nor underlying mechanism of this microbial turnover is clear. In particular, we ask whether such changes in gut profile are related to winter dietary shift and possibly beneficial to host and associated gut microbiome? Here, we integrated evidences from genomics, metagenomics, and metabolomics in three honey bee subspecies maintained at the same locality of northern China to profile both diversity and functional variations in gut bacteria across seasons. Our results showed that winter dominance of Bartonella was shared in all tested honey bee lineages. This seasonal change was likely a consequence of winter dietary shifts characterized by greatly reduced pollen consumption and accumulation of metabolic waste due to restricted excretion. Bartonella showed expanded genomic capacity in utilizing more diverse energy substrates, such as converting metabolic wastes lactate and ethanol into pyruvate, an energy source for self-utilization and possibly also for host and other symbionts. Furthermore, Bartonella was the only bacterium capable of both producing and secreting tryptophan and phenylalanine, whose metabolic products were detected in bee guts, even though all gut bacteria lacked relevant digestion enzymes. These results thus suggested a possible mechanism where the gut bacteria might benefit the host by supplementing them with essential amino acids lacking in a protein shortage diet.

Prevalence of an Insect-Associated Genomic Region in Environmentally Acquired Burkholderiaceae Symbionts

Microbial symbionts are critical for the development and survival of many eukaryotes. Recent research suggests that the genes enabling these relationships can be localized in horizontally transferred regions of microbial genomes termed "symbiotic islands." Recently, a putative symbiotic island was found that may facilitate symbioses between true bugs and numerous Burkholderia species, based on analysis of five Burkholderia symbionts. We expanded on this work by exploring the putative island's prevalence, origin, and association with colonization across the bacterial family Burkholderiaceae. We performed a broad comparative analysis of 229 Burkholderiaceae genomes, including 8 new genomes of insect- or soil-associated Burkholderia sequenced for this study. We detected the region in 23% of the genomes; these were located solely within two Burkholderia clades. Our analyses suggested that the contiguous region arose at the common ancestor of plant- and insect-associated Burkholderia clades, but the genes themselves are ancestral. Although the region was initially discovered on plasmids and we did detect two likely instances of horizontal transfer within Burkholderia, we found that the region is almost always localized to a chromosome and does not possess any of the mobility elements that typify genomic islands. Finally, to attempt to deduce the region's function, we combined our data with information on several strains' abilities to colonize the insect's symbiotic organ. Although the region was associated with improved colonization of the host, this relationship was confounded with, and likely driven by, Burkholderia clade membership. These findings advance our understanding of the genomic underpinnings of a widespread insect-microbe symbiosis. IMPORTANCE Many plants and animals form intricate associations with bacteria. These pairings can be mediated by genomic islands, contiguous regions containing numerous genes with cohesive functionality. Pathogen-associated islands are well described, but recent evidence suggests that mutualistic islands, which benefit both host and symbiont, may also be common. Recently, a putative symbiosis island was found in Burkholderia symbionts of insects. We determined that this genomic region is located in only two clades of Burkholderia (the plant- and insect-associated species) and that although it has undergone horizontal transfer, it is most likely a symbiosis-associated region rather than a true island. This region is associated with improved host colonization, although this is may be due to specific Burkholderia clades' abilities to colonize rather than presence of the region. By studying the genomic basis of the insect-Burkholderia symbiosis, we can better understand how mutualisms evolve in animals.

Dynamics of Microbial Communities across the Life Stages of Nilaparvata lugens (Stål)

Understanding the composition of microorganismal communities hosted by insect pests is an important prerequisite for revealing their functions and developing new pest control strategies. Although studies of the structure of the microbiome of Nilaparvata lugens have been published, little is known about the dynamic changes in this microbiome across different developmental stages, and an understanding of the core microbiota is still lacking. In this study, we investigated the dynamic changes in bacteria and fungi in different developmental stages of N. lugens using high-throughput sequencing technology. We observed that the microbial diversity in eggs and mated adults was higher than that in nymphs and unmated adults. We also observed a notable strong correlation between fungal and bacterial α-diversity, which suggests that fungi and bacteria are closely linked and may perform functions collaboratively during the whole developmental period. Arsenophonus and Hirsutella were the predominant bacterial and fungal taxa, respectively. Bacteria were more conserved than fungi during the transmission of the microbiota between developmental stages. Compared with that in the nymph and unmated adult stages of N. lugens, the correlation between bacterial and fungal communities in the mated adult and egg stages was stronger. Moreover, the core microbiota across all developmental stages in N. lugens was identified, and there were more bacterial genera than fungal genera; notably, the core microbiota of eggs, nymphs, and mated and unmated adults showed distinctive functional enrichment. These findings highlight the potential value of further exploring microbial functions during different developmental stages and developing new pest management strategies.

Genome-Wide Identification and Characterization of Amino Acid Polyamine Organocation Transporter Family Genes Reveal Their Role in Fecundity Regulation in a Brown Planthopper Species (Nilaparvata lugens)

The brown planthopper (BPH), Nilaparvata lugens Stål (Hemiptera:Delphacidae), is one of the most destructive pests of rice worldwide. As a sap-feeding insect, the BPH is incapable of synthesizing several amino acids which are essential for normal growth and development. Therefore, the insects have to acquire these amino acids from dietary sources or their endosymbionts, in which amino acid transporters (AATs) play a crucial role by enabling the movement of amino acids into and out of insect cells. In this study, a common amino acid transporter gene family of amino acid/polyamine/organocation (APC) was identified in BPHs and analyzed. Based on a homology search and conserved functional domain recognition, 20 putative APC transporters were identified in the BPH genome. Molecular trait analysis showed that the verified BPH APC family members were highly variable in protein features, conserved motif distribution patterns, and exon/intron organization. Phylogenetic analysis of five hemipteran species revealed an evolutionary pattern of interfamily conservation and lineage-specific expansion of this gene family. Moreover, stage- and tissue-specific expression analysis revealed diverse expression patterns in the 20 BPH APC transporter genes. Lastly, a potential BPH fecundity regulatory gene of NlAPC09 was identified and shown to participate in the fecundity regulation through the use of quantitative polymerase chain reaction (qPCR) and RNA inference experiments. Our results provide a basis for further functional investigations of APC transporters in BPH.

Diversity and dynamics of microbial communities in brown planthopper at different developmental stages revealed by high-throughput amplicon sequencing

The microbiome associated with brown planthopper (BPH) plays an important role in mediating host health and fitness. Characterization of the microbial community and its structure is prerequisite for understanding the intricate symbiotic relationships between microbes and host insect. Here, we investigated the bacterial and fungal communities of BPH at different developmental stages using high-throughput amplicon sequencing. Our results revealed that both the bacterial and fungal communities were diverse and dynamic during BPH development. The bacterial communities were generally richer than fungi in each developmental stage. At 97% similarly, 19 phyla and 278 genera of bacteria were annotated, while five fungal phyla comprising 80 genera were assigned. The highest species richness for the bacterial communities was detected in the nymphal stage. The taxonomic diversity of the fungal communities in female adults was generally at a relatively higher level when compared to other developmental stages. The most dominant phylum of bacteria and fungi at each developmental stage all belonged to Proteobacteria and Ascomycota, respectively. A significantly lower abundance of bacterial genus Acinetobacter was recorded in the egg stage when compared to other developmental stages, while the dominant fungal genus Wallemia was more abundant in the nymph and adult stages than in the egg stage. Additionally, the microbial composition differed between male and female adults, suggesting that the microbial communities in BPH were gender-dependent. Overall, our study enriches our knowledge on the microbial communities associated with BPH and will provide clues to develop potential biocontrol techniques against this rice pest.

Microbiome responses during virulence adaptation by a phloem-feeding insect to resistant near-isogenic rice lines

The microbiomes of phloem-feeding insects include functional bacteria and yeasts essential for herbivore survival and development. Changes in microbiome composition are implicated in virulence adaptation by herbivores to host plant species or host populations (including crop varieties). We examined patterns in adaptation by the green leafhopper, Nephotettix virescens, to near-isogenic rice lines (NILs) with one or two resistance genes and the recurrent parent T65, without resistance genes. Only the line with two resistance genes was effective in reducing leafhopper fitness. After 20 generations on the resistant line, selected leafhoppers attained similar survival, weight gain, and egg laying to leafhoppers that were continually reared on the susceptible recurrent parent, indicating that they had adapted to the resistant host. By sequencing the 16s rRNA gene, we described the microbiome of leafhoppers from colonies associated with five collection sites, and continually reared or switched between NILs. The microbiomes included 69-119 OTUs of which 44 occurred in ≥90% of samples. Of these, 14 OTUs were assigned to the obligate symbiont Candidatus sulcia clade. After 20 generations of selection, collection site had a greater effect than host plant on microbiome composition. Six bacteria genera, including C. sulcia, were associated with leafhopper virulence. However, there was significant within-treatment, site-related variability in the prevalence of these taxa such that the mechanisms underlying their association with virulence remain to be determined. Our results imply that these taxa are associated with leafhopper nutrition. Ours is the first study to describe microbiome diversity and composition in rice leafhoppers. We discuss our results in light of the multiple functions of herbivore microbiomes during virulence adaptation in insect herbivores.

Community structure, dispersal ability and functional profiling of microbiome existing in fat body and ovary of the brown planthopper, Nilaparvata lugens

The endosymbionts play vital roles in growth, development and reproduction in insects. Yeast-like endosymbionts (YLSs) have been well studied in Nilaparvata lugens (N. lugens), but little is known about the tissue-specific bacterial microbiomes, especially on the microbial intersection among internal tissues. Here, the correlation of microbial composition, structure, dispersal ability and functional profiling were illuminated in two tissues, the fat body and ovary in N. lugens. A total of 11 phyla and 105 genera were captured from all samples; Firmicutes and Proteobacteria were the most predominant and accounted for more than 99% in all samples. However, the relative abundance of Firmicutes and Proteobacteria was significantly different in ovary and fat body through Fisher's Least Significant Difference test. Microbial diversity but not the richness index in the two tissues exhibited significant difference. Furthermore, the microbial community structure of the ovary and fat body were primarily determined by tissue quality. Firmicutes showed strong dispersal ability between ovary and fat body based on the quantitative null model assessing, indicating the frequent interaction of these microbiomes in the two tissues. In addition, the Kyoto Encyclopedia of Genes and Genomes pathways of microbial participation were delineated. The ten most abundant pathways counted for over 46% of the annotation and were shared between the two tissues, mainly containing Energy Metabolism and Amino Acid Metabolism/Biosynthesis. The results will provide insights into the correlation of microbial community structure between ovary and fat body of N. lugens.

Metabolic responses of brown planthoppers to IR56 resistant rice cultivar containing multiple resistance genes

The brown planthopper (Nilaparvata lugens Stål, BPH) is one of the most destructive pests in rice production, and rice resistance is thought to be an economical and environmentally friendly strategy against BPH. Although resistant rice cultivars have been widely applied to control BPH, little is known regarding the impact of the ingestion of resistant plant phloem on the BPH physiological metabolism. In this study, the differences in the metabolic responses of BPH nymphs during the first 72 h after ingesting susceptible TN1 and resistant IR56 plant phloem were compared. The results showed that BPH nymphs feeding on IR56 plants exhibited significant decreases in honeydew excretion and body weight, and significantly lower concentrations of most of the detected sugars, vitamins and some essential amino acids but higher levels of most amides, free fatty acids and some non-essential amino acids. These findings indicate that the energy metabolism and nutrition supply of these nymphs were disturbed by the resistant rice plants. The qPCR results revealed that BPH could actively adapt to IR56 plants by upregulating the gene expression levels of some detoxification enzymes, including GST, CarE and POD, to some extent. These results provide additional information to improve our understanding of physiological mechanism underlying the loss of BPH fitness caused by resistant rice varieties.

Dual "Bacterial-Fungal" Symbiosis in Deltocephalinae Leafhoppers (Insecta, Hemiptera, Cicadomorpha: Cicadellidae)

The symbiotic systems (types of symbionts, their distribution in the host insect body, and their transovarial transmission between generations) of four Deltocephalinae leafhoppers: Fieberiella septentrionalis, Graphocraerus ventralis, Orientus ishidae, and Cicadula quadrinotata have been examined by means of histological, ultrastructural, and molecular techniques. In all four species, two types of symbionts are present: bacterium Sulcia (phylum Bacteroidetes) and yeast-like symbionts closely related to the entomopathogenic fungi (phylum Ascomycota, class Sordariomycetes). Sulcia bacteria are always harbored in giant bacteriocytes, which are grouped into large organs termed "bacteriomes." In F. septentrionalis, G. ventralis, and O. ishidae, numerous yeast-like microorganisms are localized in cells of the fat body, whereas in C. quadrinotata, they occupy the cells of midgut epithelium in large number. Additionally, in C. quadrinotata, a small amount of yeast-like microorganisms occurs intracellularly in the fat body cells and, extracellularly, in the hemolymph. Sulcia bacteria in F. septentrionalis, G. ventralis, O. ishidae, and C. quadrinotata, and the yeast-like symbionts residing in the fat body of F. septentrionalis, G. ventralis, and O. ishidae are transovarially transmitted; i.e., they infect the ovarioles which constitute the ovaries.

Knockdown of a putative argininosuccinate lyase gene reduces arginine content and impairs nymphal development in Nilaparvata lugens

Nilaparvata lugens is a typical phloem feeder. Rice phloem is high in simple sugars and very low in essential amino acids. Nilaparvata lugens harbors an ascomycete Entomomyces delphacidicola that hypothetically biosynthesizes several amino acids to meet the nutrition requirement of the planthopper. Among these amino acids, here, we focused on arginine biosynthesis. A complete cDNA of an E. delphacidicola gene, arginine-succinate lyase, EdArg4, the last step in arginine biosynthesis, was obtained. RNAi-mediated suppression of EdArg4 reduced arginine content in the hemolymph, and decreased the expression of several arginine biosynthesis genes. Silencing of EdArg4 delayed nymphal development and led to nymphal lethality. About 20% of the EdArg4 RNAi surviving adults were deformed. The most obvious defect was wider and larger abdomen. The EdArg4 RNAi-treated planthoppers had thickened wings and enlarged antennae, legs, and anal tubes and a few adults did not normally emerge. Arginine deficiency in the EdArg4 RNAi planthoppers repressed nitric oxide signaling, determined at the transcriptional level. We infer that E. delphacidicola biosynthesizes essential arginine to compensate for nutrition deficiency in N. lugens.

Reference genes for quantitative real-time PCR analysis in symbiont Entomomyces delphacidicola of Nilaparvata lugens (Stål)

Nilaparvata lugens (Stål) (Hemiptera: Delphacidae) is a major rice pest that harbors an endosymbiont ascomycete fungus, Entomomyces delphacidicola str. NLU (also known as yeast-like symbiont, YLS). Driving by demand of novel population management tactics (e.g. RNAi), the importance of YLS has been studied and revealed, which greatly boosts the interest of molecular level studies related to YLS. The current study focuses on reference genes for RT-qPCR studies related to YLS. Eight previously unreported YLS genes were cloned, and their expressions were evaluated for N. lugens samples of different developmental stages and sexes, and under different nutritional conditions and temperatures. Expression stabilities were analyzed by BestKeeper, geNorm, NormFinder, ΔCt method and RefFinder. Furthermore, the selected reference genes for RT-qPCR of YLS genes were validated using targeted YLS genes that respond to different nutritional conditions (amino acid deprivation) and RNAi. The results suggest that ylsRPS15p/ylsACT are the most suitable reference genes for temporal gene expression profiling, while ylsTUB/ylsACT and ylsRPS15e/ylsGADPH are the most suitable reference gene choices for evaluating nutrition and temperature effects. Validation studies demonstrated the advantage of using endogenous YLS reference genes for YLS studies.

A Genome-Wide Identification and Analysis of the Basic Helix-Loop-Helix Transcription Factors in Brown Planthopper, Nilaparvata lugens

The basic helix-loop-helix (bHLH) transcription factors in insects play essential roles in multiple developmental processes including neurogenesis, sterol metabolism, circadian rhythms, organogenesis and formation of olfactory sensory neurons. The identification and function analysis of bHLH family members of the most destructive insect pest of rice, Nilaparvata lugens, may provide novel tools for pest management. Here, a genome-wide survey for bHLH sequences identified 60 bHLH sequences (NlbHLHs) encoded in the draft genome of N. lugens. Phylogenetic analysis of the bHLH domains successfully classified these genes into 40 bHLH families in group A (25), B (14), C (10), D (1), E (8) and F (2). The number of NlbHLHs with introns is higher than many other insect species, and the average intron length is shorter than those of Acyrthosiphon pisum. High number of ortholog families of NlbHLHs was found suggesting functional conversation for these proteins. Compared to other insect species studied, N. lugens has the highest number of bHLH members. Furthermore, gene duplication events of SREBP, Kn(col), Tap, Delilah, Sim, Ato and Crp were found in N. lugens. In addition, a putative full set of NlbHLH genes is defined and compared with another insect species. Thus, our classification of these NlbHLH members provides a platform for further investigations of bHLH protein functions in the regulation of N. lugens, and of insects in general.

ATP phosphoribosyltransferase from symbiont Entomomyces delphacidicola invovled in histidine biosynthesis of Nilaparvata lugens (Stål)

Histidine is an essential amino acid assumed to be synthesized by an obligatory yeast-like symbiont (Entomomyces delphacidicola str. NLU) in Nilaparvata lugens, an important rice pest. The adenosine-triphosphate phosphoribosyltransferase (ATP-PRTase) facilities the committed first step of the histidine biosynthesis pathway. In the current study, a putative ATP-PRTase was cloned and verified to be of E. delphacidicola origin (EdePRTase). The expression of the gene was spatial and temporal universal with a profile that matched the distribution of the fungal symbiont. RNA interference aided the knockdown of the EdePRTase-suppressed EdePRTase expression by 32-48 %. Hemolymph histidine level was also reduced followed by significant reduction of adult body weight. However, other performance characters including nymph development, survival, and adult sex ratio were not adversely affected by the knockdown. Furthermore, forced histidine exposure (through injection or feeding) significantly inhibited the EdePRTase mRNA levels at higher concentrations, but significantly increased EdePRTase expression levels at lower concentrations (feeding only). The significance of these findings support that the EdePRTase is from symbiont E. delphacidicola, and its involvement in histidine biosynthesis of N. lugens was discussed. The results provide a better understanding of EdePRTase and the encoded functional ATP-PRTase enzyme regulation in N. lugens and insects in general.

Knocking down a putative Δ(1) -pyrroline-5-carboxylate dehydrogenase gene by RNA interference inhibits flight and causes adult lethality in the Colorado potato beetle Leptinotarsa decemlineata (Say)

BACKGROUND

Leptinotarsa decemlineata is an able disperser by flight. Novel control strategies must be explored to control the damage and inhibit the dispersal efficiently. Proline is a major energy substrate during flight. Δ-Pyrroline-5-carboxylate dehydrogenase (P5CDh) catalyses the second step of proline degradation for the production of ATP.

RESULTS

A full-length Ldp5cdh cDNA was cloned. Ldp5cdh was ubiquitously expressed in the eggs, the first through fourth larval instars, wandering larvae, pupae and adults. In the adults, Ldp5cdh mRNA was widely distributed in thorax muscles, midgut, foregut, hindgut, Malpighian tubules, ventral ganglion, fat body and epidermis, with the expression levels from the highest to the lowest. Two double-stranded RNAs (dsRNAs) (dsLdp5cdh1 and dsLdp5cdh2) targeting Ldp5cdh were constructed and bacterially expressed. Ingestion of dsLdp5cdh1 and dsLdp5cdh2 successfully silenced Ldp5cdh, significantly increased the contents of proline, arginine and alanine, but strongly decreased the contents of asparate, asparagine, glutamate and glutamine in the haemolymph. Moreover, knocking down Ldp5cdh significantly reduced ATP content, decreased flight speed, shortened flight distance and increased adult mortality.

CONCLUSIONS

It seems that identified Ldp5cdh encodes a functional P5CDh enzyme, and Ldp5cdh may serve as a potential target for dsRNA-based pesticide for controlling the damage and dispersal of L. decemlineata adults. © 2014 Society of Chemical Industry.

RNA interference-aided knockdown of a putative saccharopine dehydrogenase leads to abnormal ecdysis in the brown planthopper, Nilaparvata lugens (Stål) (Hemiptera: Delphacidae)

The brown planthopper Nilaparvata lugens is a serious phloem-feeding pest of rice in China. The current study focuses on a saccharopine dehydrogenase (SDH) that catalyzes the penultimate reaction in biosynthesis of the amino acid lysine (Lys), which plays a role in insect growth and carnitine production (as a substrate). The protein, provisionally designated as NlylsSDH [a SDH derived from yeast-like symbiont (YLS) in N. lugens], had a higher transcript level in abdomens, compared with heads, wings, legs and thoraces, which agrees with YLS distribution in N. lugens. Ingestion of Nlylssdh targeted double-stranded RNA (dsNlylssdh) for 5, 10 and 15 days decreased the mRNA abundance in the hoppers by 47, 70 and 31%, respectively, comparing with those ingesting normal or dsegfp diets. Nlylssdh knockdown slightly decreased the body weights, significantly delayed the development of females, and killed approximately 30% of the nymphs. Moreover, some surviving adults showed two apparent phenotypic defects: wing deformation and nymphal cuticles remained on tips of the legs and abdomens. The brachypterours/macropterours and sex ratios (female/male) of the adults on the dsRNA diet were lowered compared with the adults on diets without dsRNA. These results suggest that Nlylssdh encodes a functional SDH protein. The adverse effect of Nlylssdh knockdown on N. lugens implies the importance of Lys in hopper development. This study provides a proof of concept example that Nlylssdh could serve as a possible dsRNA-based pesticide for planthopper control.

Rice stripe virus counters reduced fecundity in its insect vector by modifying insect physiology, primary endosymbionts and feeding behavior

Virus-vector relationships can be complex and diverse as a result of long-term coevolution. Understanding these interactions is crucial for disease and vector management. Rice stripe virus (RSV) is known to be transovarially transmitted within its vector, Laodelphax striatellus, and causes serious rice stripe disease. In RSV-infected L. striatellus, we found contrasting changes in vector fecundity, physiology, primary endosymbionts (i.e. yeast-like symbionts, YLS) and feeding behavior that can interact to affect the spread of RSV. RSV-infected L. striatellus exhibited a significant decrease in fecundity that could lead a reduction of viruliferous individuals in populations. As a potential response to this loss, RSV infection also significantly shortened nymphal stage duration, which can strengthen RSV vertical circulation in L. striatellus populations and promote RSV spreading by adult migration and dispersal. Down-regulated JHAMT and up-regulated CYP307A1 in the juvenile hormone and ecdysteroid pathways, respectively, were linked to accelerated development. RSV-infected adults were also found to have higher body weight in conjunction with increased YLS abundance. Furthermore, prolonged host plant phloem exposure to salivation by RSV-infected adults should further enhance RSV horizontal transmission. Our study highlights potential strategies of RSV in enhancing its transmission, and provides new insights into the complexity of virus-vector interactions.

Pathways of Amino Acid Degradation in Nilaparvata lugens (Stål) with Special Reference to Lysine-Ketoglutarate Reductase/Saccharopine Dehydrogenase (LKR/SDH)

Nilaparvata lugens harbors yeast-like symbionts (YLSs). In present paper, a genome-wide analysis found 115 genes from Ni. lugens and 90 genes from YLSs that were involved in the metabolic degradation of 20 proteinogenic amino acids. These 205 genes encoded for 77 enzymes. Accordingly, the degradation pathways for the 20 amino acids were manually constructed. It is postulated that Ni. lugens can independently degrade fourteen amino acids (threonine, alanine, glycine, serine, aspartate, asparagine, phenylalanine, tyrosine, glutamate, glutamine, proline, histidine, leucine and lysine). Ni. lugens and YLSs enzymes may work collaboratively to break down tryptophan, cysteine, arginine, isoleucine, methionine and valine. We cloned a lysine-ketoglutarate reductase/saccharopine dehydrogenase gene (Nllkr/sdh) that encoded a bifunctional enzyme catalyzing the first two steps of lysine catabolism. Nllkr/sdh is widely expressed in the first through fifth instar nymphs and adults, and is highly expressed in the fat body, ovary and gut in adults. Ingestion of dsNllkr/sdh by nymphs successfully knocked down the target gene, and caused nymphal/adult mortality, shortened nymphal development stage and reduced adult fresh weight. Moreover, Nllkr/sdh knockdown resulted in three defects: wings were shortened and thickened; cuticles were stretched and thinned; and old nymphal cuticles remained on the tips of legs and abdomen and were not completely shed. These data indicate that impaired lysine degradation negatively affects the survival and development of Ni. lugens.

Genomes of the rice pest brown planthopper and its endosymbionts reveal complex complementary contributions for host adaptation

Background

The brown planthopper, Nilaparvata lugens, the most destructive pest of rice, is a typical monophagous herbivore that feeds exclusively on rice sap, which migrates over long distances. Outbreaks of it have re-occurred approximately every three years in Asia. It has also been used as a model system for ecological studies and for developing effective pest management. To better understand how a monophagous sap-sucking arthropod herbivore has adapted to its exclusive host selection and to provide insights to improve pest control, we analyzed the genomes of the brown planthopper and its two endosymbionts.

Results

We describe the 1.14 gigabase planthopper draft genome and the genomes of two microbial endosymbionts that permit the planthopper to forage exclusively on rice fields. Only 40.8% of the 27,571 identified Nilaparvata protein coding genes have detectable shared homology with the proteomes of the other 14 arthropods included in this study, reflecting large-scale gene losses including in evolutionarily conserved gene families and biochemical pathways. These unique genomic features are functionally associated with the animal’s exclusive plant host selection. Genes missing from the insect in conserved biochemical pathways that are essential for its survival on the nutritionally imbalanced sap diet are present in the genomes of its microbial endosymbionts, which have evolved to complement the mutualistic nutritional needs of the host.

Conclusions

Our study reveals a series of complex adaptations of the brown planthopper involving a variety of biological processes, that result in its highly destructive impact on the exclusive host rice. All these findings highlight potential directions for effective pest control of the planthopper.

Electronic supplementary material

The online version of this article (doi:10.1186/s13059-014-0521-0) contains supplementary material, which is available to authorized users.

A putative Δ1-pyrroline-5-carboxylate synthetase involved in the biosynthesis of proline and arginine in Leptinotarsa decemlineata

Delta 1-pyrroline-5-carboxylate synthetase (P5CS) catalyzes the conversion of glutamate (Glu) to Glu semialdehyde (GSA). GSA spontaneously cyclizes to form P5C. P5C is then reduced to proline (Pro) or is converted to ornithine, the intermediate for arginine (Arg) biosynthesis. In the present study, a full-length Ldp5cs complementary DNA was cloned from the Colorado potato beetle Leptinotarsa decemlineata, a notorious insect defoliator of potato in most potato-growing regions of the world. Ldp5cs encodes a 792-amino-acid protein which shares high identity to homologues from other insect species. Quantitative reverse transcription polymerase chain reaction revealed that Ldp5cs was ubiquitously expressed in the eggs, first to fourth-instar larvae, wandering larvae, pupae and sexually mature adults. In the adults, Ldp5cs mRNA levels were higher in the fat body, foregut, midgut and hindgut, moderate in the ventral ganglion, lower in the thorax muscles, epidermis and Malpighian tubules. Two double-stranded RNAs (dsRNAs) (dsLdp5cs1 and dsLdp5cs2) targeting Ldp5cs were constructed and bacterially expressed. Ingestion during 3 consecutive days of dsLdp5cs1 or dsLdp5cs2 successfully silenced Ldp5cs, significantly reduced the contents of Pro and Arg in the hemolymph, decreased flight speed and shortened flight distance of the resulting adults. Furthermore, knocking down Ldp5cs significantly increased adult mortality. Thus, our results suggest that identified Ldp5cs encodes a functional P5CS enzyme that is involved in the biosynthesis of Pro and Arg in L. decemlineata.