Sequence variation in trypsin- and chymotrypsin-like cDNAs from the midgut of Ostrinia nubilalis: methods for allelic differentiation of candidate Bacillus thuringiensis resistance genes

Sugarcane giant borer transcriptome analysis and identification of genes related to digestion

Sugarcane is a widely cultivated plant that serves primarily as a source of sugar and ethanol. Its annual yield can be significantly reduced by the action of several insect pests including the sugarcane giant borer (Telchin licus licus), a lepidopteran that presents a long life cycle and which efforts to control it using pesticides have been inefficient. Although its economical relevance, only a few DNA sequences are available for this species in the GenBank. Pyrosequencing technology was used to investigate the transcriptome of several developmental stages of the insect. To maximize transcript diversity, a pool of total RNA was extracted from whole body insects and used to construct a normalized cDNA database. Sequencing produced over 650,000 reads, which were de novo assembled to generate a reference library of 23,824 contigs. After quality score and annotation, 43% of the contigs had at least one BLAST hit against the NCBI non-redundant database, and 40% showed similarities with the lepidopteran Bombyx mori. In a further analysis, we conducted a comparison with Manduca sexta midgut sequences to identify transcripts of genes involved in digestion. Of these transcripts, many presented an expansion or depletion in gene number, compared to B. mori genome. From the sugarcane giant borer (SGB) transcriptome, a number of aminopeptidase N (APN) cDNAs were characterized based on homology to those reported as Cry toxin receptors. This is the first report that provides a large-scale EST database for the species. Transcriptome analysis will certainly be useful to identify novel developmental genes, to better understand the insect's biology and to guide the development of new strategies for insect-pest control.

Effects of different dietary conditions on the expression of trypsin- and chymotrypsin-like protease genes in the digestive system of the migratory locust, Locusta migratoria

While technological advancements have recently led to a steep increase in genomic and transcriptomic data, and large numbers of protease sequences are being discovered in diverse insect species, little information is available about the expression of digestive enzymes in Orthoptera. Here we describe the identification of Locusta migratoria serine protease transcripts (cDNAs) involved in digestion, which might serve as possible targets for pest control management. A total of 5 putative trypsin and 15 putative chymotrypsin gene sequences were characterized. Phylogenetic analysis revealed that these are distributed among 3 evolutionary conserved clusters. In addition, we have determined the relative gene expression levels of representative members in the gut under different feeding conditions. This study demonstrated that the transcript levels for all measured serine proteases were strongly reduced after starvation. On the other hand, larvae of L. migratoria displayed compensatory effects to the presence of Soybean Bowman Birk (SBBI) and Soybean Trypsin (SBTI) inhibitors in their diet by differential upregulation of multiple proteases. A rapid initial upregulation was observed for all tested serine protease transcripts, while only for members belonging to class I, the transcript levels remained elevated after prolonged exposure. In full agreement with these results, we also observed an increase in proteolytic activity in midgut secretions of locusts that were accustomed to the presence of protease inhibitors in their diet, while no change in sensitivity to these inhibitors was observed. Taken together, this paper is the first comprehensive study on dietary dependent transcript levels of proteolytic enzymes in Orthoptera. Our data suggest that compensatory response mechanisms to protease inhibitor ingestion may have appeared early in insect evolution.

Characterization and transcriptional analyses of cDNAs encoding three trypsin- and chymotrypsin-like proteinases in Cry1Ab-susceptible and Cry1Ab-resistant strains of sugarcane borer, Diatraea saccharalis

Diatraea saccharalis is a major corn borer pest. Midgut serine proteinases are essential for insect growth and development. Alteration of midgut proteinases is responsible for Bt resistance development in some species. To clone midgut trypsin and chymotrypsin cDNAs and to test if the Cry1Ab resistance in D. saccharalis is associated with changes in midgut proteinases, total midgut tryptic and chymotryptic activities, cDNA sequences, and gene expressions of three trypsin and three chymotrypsin genes were comparatively examined between Cry1Ab-susceptible (Cry1Ab-SS) and Cry1Ab-resistant (Cry1Ab-RR) strains. Full-length cDNAs encoding three trypsin- and three chymotrypsin-like proteinases were sequenced from Cry1Ab-SS and Cry1Ab-RR larvae. These cDNAs code for active forms of midgut serine proteinases with all functional motifs, including signal peptide, conserved His-Asp-Ser for the catalytic triad, three pairs of cysteines for disulfide bridge configurations, and conserved substrate specificity determination residues. In general, cDNA and putative protein sequences are highly similar between Cry1Ab-SS and Cry1Ab-RR strains, except for a few nucleotide and predicted amino acid substitutions, whose function need to be further clarified. Total trypsin and chymotrypsin activities were also similar between Cry1Ab-SS and Cry1Ab-RR strains. Transcriptional levels of the trypsin and chymotrypsin genes had numerical difference between Cry1Ab-SS and Cry1Ab-RR strains, but the difference was not statistically significant. Data suggest that the development of Cry1Ab resistance in D. saccharalis was not significantly associated with these trypsins and chymotrypsins. Results clarified the role of six midgut proteinases and provided a foundation for continuing examination of potential involvement of other midgut proteinases in Bt resistance development and other important biochemical processes.

Serine and cysteine protease-like genes in the genome of a gall midge and their interactions with host plant genotypes

Proteases play important roles in a wide range of physiological processes in organisms. For plant-feeding insects, digestive proteases are targets for engineering protease inhibitors for pest control. In this study, we identified 105 putative serine- and cysteine-protease genes from the genome of the gall midge Mayetiola destructor (commonly known as Hessian fly), a destructive pest of wheat. Among the genes, 31 encode putative trypsins, 18 encode putative chymotrypsins, seven encode putative cysteine proteases, and the remaining may encode either other proteases or protease homologues. Developmental stage- and tissue-specific expression profiles of the genes encoding putative trypsins, chymotrypsins, and cysteine proteases were determined by quantitative reverse-transcription PCR. Comparative analyses of stage- and tissue-specific expression patterns suggested that several genes are likely to encode digestive proteases in the M. destructor larval gut, including genes encoding putative trypsins MDP3, MDP5, MDP9, MDP24, MDP48, MDP51, MDP57, MDP61, MDP71, and MDP90; genes encoding putative chymotrypsins MDP1, MDP7, MDP8, MDP18, MDP19, and MDP20; and genes encoding putative cysteine proteases MDP95 and MDP104. The expression of some protease genes was affected by plant genotypes. Genes encoding trypsins MDP3, MDP9, and MPD23, chymotrypsins MDP20 and MDP21, and cysteine proteases MDP99 and MDP104 were upregulated in M. destructor larvae feeding in resistant plants, whereas genes encoding trypsins MDP12, MDP24, and MDP33, and chymotrypsins mdp8, mdp15, and mdp16 were downregulated in M. destructor larvae feeding in resistant plants. This study provides a foundation for further comparative studies on proteases in different insects, and further characterization of M. destructor digestive proteases and their interactions with host plants, as well as potential targets for transgenic wheat plants.

In vitro antiviral activity of an alkaline trypsin from the digestive juice of Bombyx mori larvae against nucleopolyhedrovirus

Alkaline trypsin protein of molecular mass 25,436 Da purified from the digestive juice of Bombyx mori larvae indicated strong antiviral activity against Bombyx mori nucleopolyhedrovirus (BmNPV) under in vitro conditions. Partial N-terminal amino acid sequence of the protein was determined and the cDNA was cloned based on the amino acid sequence. A homology search of the deduced amino acid sequence of the cDNA showed 55% identity with Helicoverpa armigera trypsin and the active site of this protein was completely conserved. Hence, the protein was designated B. mori trypsin (Bmtryp). The results suggest that Bmtryp, an insect digestive enzyme, can be a potential antiviral factor against BmNPV at the initial site of viral infection.

Second-generation sequencing supply an effective way to screen RNAi targets in large scale for potential application in pest insect control

The key of RNAi approach success for potential insect pest control is mainly dependent on careful target selection and a convenient delivery system. We adopted second-generation sequencing technology to screen RNAi targets. Illumina's RNA-seq and digital gene expression tag profile (DGE-tag) technologies were used to screen optimal RNAi targets from Ostrinia furnalalis. Total 14690 stage specific genes were obtained which can be considered as potential targets, and 47 were confirmed by qRT-PCR. Ten larval stage specific expression genes were selected for RNAi test. When 50 ng/µl dsRNAs of the genes DS10 and DS28 were directly sprayed on the newly hatched larvae which placed on the filter paper, the larval mortalities were around 40∼50%, while the dsRNAs of ten genes were sprayed on the larvae along with artificial diet, the mortalities reached 73% to 100% at 5 d after treatment. The qRT-PCR analysis verified the correlation between larval mortality and the down-regulation of the target gene expression. Topically applied fluorescent dsRNA confirmed that dsRNA did penetrate the body wall and circulate in the body cavity. It seems likely that the combination of DGE-tag with RNA-seq is a rapid, high-throughput, cost less and an easy way to select the candidate target genes for RNAi. More importantly, it demonstrated that dsRNAs are able to penetrate the integument and cause larval developmental stunt and/or death in a lepidopteron insect. This finding largely broadens the target selection for RNAi from just gut-specific genes to the targets in whole insects and may lead to new strategies for designing RNAi-based technology against insect damage.

A midgut-specific chymotrypsin cDNA (Slctlp1) from Spodoptera litura: cloning, characterization, localization and expression analysis

Serine proteases play important roles in food digestion and immune response during insect development. A full-length cDNA (Slctlp1) encoding a chymotrypsin-like serine protease was cloned from Spodoptera litura and characterized for its cDNA structure, developmental and induced expression and localization. The deduced protein of the Slctlp1 cDNA contains a catalytic triad and a substrate specificity pocket found in most of the serine proteases. Both the transcripts and protein of Slctlp1 were predominately expressed in the midgut at the feeding stages during the larval development. Immunohistochemistry analysis indicated that the SLCTLP1 protein was predominately present in the midgut of the 6th instar feeding larvae. Starvation suppressed the expression of Slctlp1 gene and protein in 6th instar larvae and the protein expression was increased again by re-feeding the insect. The results suggest that the cloned Slctlp1 cDNA may be involved in food protein digestion at the feeding stages during larval development.

A chymotrypsin-like serine protease cDNA involved in food protein digestion in the common cutworm, Spodoptera litura: Cloning, characterization, developmental and induced expression patterns, and localization

A full-length cDNA (Slctlp2) encoding a chymotrypsin-like serine protease was cloned from Spodoptera litura. This cDNA encoded a putative serine protease with a predicted molecular mass of 30.6kDa, which contained a serine protease catalytic motif GDSGGPL. Temporal and spatial expression of Slctlp2 mRNA and protein detected by Northern blotting, RT-PCR, qPCR and Western blotting analyses revealed that both Slctlp2 mRNA and protein were mainly present in the foregut and midgut of the 5th and 6th instar larvae during the feeding stages. In situ hybridization and immunohistochemistry confirmed that both Slctlp2 mRNA and protein were predominately present in the midgut. Expression of the gene was not induced by bacterial infection. Juvenile hormone III induced the gene expression, while 20-hydroxyecdysone had no impact on the expression. The expression of Slctlp2 mRNA and protein was down-regulated by starvation but up-regulated by re-feeding. The SlCTLP2 protein was detected in the lumen residues of the anterior, middle and posterior midgut and feces of the feeding 6th instar larvae, suggesting that it was secreted from the epithelium into the lumen of the gut. The results suggest that this Slctlp2 gene may be involved in digestive process of food proteins during the feeding stages of the larval development.

Mining an Ostrinia nubilalis midgut expressed sequence tag (EST) library for candidate genes and single nucleotide polymorphisms (SNPs)

Genes expressed in lepidopteran midgut tissues are involved in digestion and Bacillus thuringiensis (Bt) toxin resistance traits. Five hundred and thirty five unique transcripts were annotated from 1745 high quality O. nubilalis larval midgut expressed sequence tags (ESTs). Full-length cDNA sequence of 12 putative serine proteinase genes and 3 partial O. nubilalis aminopeptidase N protein genes, apn1, apn3, and apn4, were obtained, and genes may have roles in plant feeding and Bt toxin resistance traits of Ostrinia larvae. The EST library was not normalized and insert frequencies reflect transcript levels under the initial treatment conditions and redundancy of inserts from highly expressed transcripts allowed prediction of putative single nucleotide polymorphisms (SNPs). Ten di-, tri- or tetranucleotide repeat unit microsatellite loci were identified, and minisatellite repeats were observed within the C-termini of two encoded serine proteinases. Molecular markers showed polymorphism at 28 SNP loci and one microsatellite locus, and Mendelian inheritance indicated that markers were applicable to genome mapping applications. This O. nubilalis larval midgut EST collection is a resource for gene discovery, expression information, and allelic variation for use in genetic marker development.

Expressed sequence tags from the midgut of Epiphyas postvittana (Walker) (Lepidoptera: Tortricidae)

The midgut is a key tissue in insect science. Physiological roles include digestion and peritrophic membrane function, as well as being an important target for insecticides. We used an expressed sequence tag (EST) approach to identify candidate genes and gene families involved in these processes in the light brown apple moth, Epiphyas postvittana (Walker) (Lepidoptera: Tortricidae). Two cDNA libraries were constructed from dissected midgut of third to fifth instar larvae. Clustering analysis of 6416 expressed sequence tags produced 1178 tentative unique genes comprising 725 tentative contigs and 453 singletons. The sequences show similar codon usage to sequences from other lepidopterans, a Kozak consensus sequence similar to Drosophila and single nucleotide polymorphisms (SNPs) were detected at a frequency of 1.35/kb. The identity of the most common Interpro families correlates well with major known functions of the midgut. Phylogenetic analysis was conducted on representative sequences from selected multigene families. Gene families include a broad range of digestive proteases, lipases and carbohydrases that appear to have degradative capacity against the major food components found in leaves, the diet of these larvae; and carboxylesterases, glutathione-S-transferases and cytochrome P450 monooxygenases, potentially involved in xenobiotic degradation. Two of the larger multigene families, serine proteases and lipases, expressed a high proportion of genes that are likely to be catalytically inactive.