Characterization of light-dependent rhythm of courtship vibrational signals in Nilaparvata lugens: essential involvement of cryptochrome genes

BACKGROUND

Vibrational signal plays a crucial role in courtship communication in many insects. However, it remains unclear whether insect vibrational signals exhibit daily rhythmicity in response to changes in environmental cues.

RESULTS

In this study, we observed daily rhythms of both female vibrational signals (FVS) and male vibrational signals (MVS) in the brown planthopper (BPH), Nilaparvata lugens (Stål), one of the most notorious rice pests across Asia. Notably, oscillations of FVS and MVS in paired BPHs were synchronized as part of male-female duetting interactions, displaying significant day-night rhythmicity. Furthermore, we observed light dependency of FVS emissions under different photoperiodic regimes (18 L:6 D and 6 L:18 D) and illumination intensity levels (>300 lx, 50 lx, and 25 lx). Subsequently, the potential role of circadian clock genes cryptochromes (Nlcry1 and Nlcry2) in regulating FVS daily oscillations was examined using gene knockdown via RNA interference. We observed sharp declines and disrupted rhythms in FVS frequencies when either of the Nlcrys was downregulated, with Nlcry2 knockdown showing a more prominent effect. Moreover, we recorded a novel FVS variant (with a dominant frequency of 361.76 ± 4.31 Hz) emitted by dsNlcry1-treated BPH females, which significantly diminished the impact of courtship stimuli on receptive males.

CONCLUSION

We observed light-dependent daily rhythms of substrate-borne vibrational signals (SBVS) in BPH and demonstrated essential yet distinct roles of the two Nlcrys. These findings enhanced our understanding of insect SBVS and illustrated the potential of novel precision physical control strategies for disrupting mating behaviors in this rice pest. © 2023 Society of Chemical Industry.

Defense Regulatory Network Associated with circRNA in Rice in Response to Brown Planthopper Infestation

The brown planthopper (BPH), Nilaparvata lugens (Stål), a rice-specific pest, has risen to the top of the list of significant pathogens and insects in recent years. Host plant-mediated resistance is an efficient strategy for BPH control. Nonetheless, BPH resistance in rice cultivars has succumbed to the emergence of distinct virulent BPH populations. Circular RNAs (circRNAs) play a pivotal role in regulating plant-environment interactions; however, the mechanisms underlying their insect-resistant functions remain largely unexplored. In this study, we conducted an extensive genome-wide analysis using high-throughput sequencing to explore the response of rice circRNAs to BPH infestations. We identified a total of 186 circRNAs in IR56 rice across two distinct virulence groups: IR-IR56-BPH (referring to IR rice infested by IR56-BPH) and IR-TN1-BPH, along with a control group (IR-CK) without BPH infestation. Among them, 39 circRNAs were upregulated, and 43 circRNAs were downregulated in the comparison between IR-IR56-BPH and IR-CK. Furthermore, in comparison with IR-CK, 42 circRNAs exhibited upregulation in IR-TN1-BPH, while 42 circRNAs showed downregulation. The Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analysis revealed that the targets of differentially expressed circRNAs were considerably enriched in a multitude of biological processes closely linked to the response to BPH infestations. Furthermore, we assessed a total of 20 randomly selected circRNAs along with their corresponding expression levels. Moreover, we validated the regulatory impact of circRNAs on miRNAs and mRNAs. These findings have led us to construct a conceptual model that circRNA is associated with the defense regulatory network in rice, which is likely facilitated by the mediation of their parental genes and competing endogenous RNA (ceRNA) networks. This model contributes to the understanding of several extensively studied processes in rice-BPH interactions.

Roles of GFAT and PFK genes in energy metabolism of brown planthopper, Nilaparvata lugens

Glutamine:fructose-6-phosphate aminotransferases (GFATs) and phosphofructokinase (PFKs) are the principal rate-limiting enzymes involved in hexosamine biosynthesis pathway (HBP) and glycolysis pathway, respectively. In this study, the NlGFAT and NlPFK were knocked down through RNA interference (RNAi) in Nilaparvata lugens, the notorious brown planthopper (BPH), and the changes in energy metabolism were determined. Knockdown of either NlGFAT or NlPFK substantially reduced gene expression related to trehalose, glucose, and glycogen metabolism pathways. Moreover, trehalose content rose significantly at 72 h after dsGFAT injection, and glycogen content increased significantly at 48 h after injection. Glucose content remained unchanged throughout the experiment. Conversely, dsPFK injection did not significantly alter trehalose, but caused an extreme increase in glucose and glycogen content at 72 h after injection. The Knockdown of NlGFAT or NlPFK significantly downregulated the genes in the glycolytic pathway, as well as caused a considerable and significant decrease in pyruvate kinase (PK) activity after 48 h and 72 h of inhibition. After dsGFAT injection, most of genes in TCA cycle pathway were upregulated, but after dsNlPFK injection, they were downregulated. Correspondingly, ATP content substantially increased at 48 h after NlGFAT knockdown but decreased to an extreme extent by 72 h. In contrast, ATP content decreased significantly after NlPFK was knocked down and returned. The results have suggested the knockdown of either NlGFAT or NlPFK resulted in metabolism disorders in BPHs, highlighting the difference in the impact of those two enzyme genes on energy metabolism. Given their influence on BPHs energy metabolism, developing enzyme inhibitors or activators may provide a biological control for BPHs.

Knockdown of the chromatin remodeling ATPase gene Brahma impairs the reproductive potential of the brown planthopper, Nilaparvata lugens

The brown planthopper (BPH), Nilaparvata lugens (Stål), is one of the most destructive pests in rice-growing regions of Asia. Extensive studies have suggested that SWI/SNF chromatin remodeling ATPase Brahma (BRM) plays multiple roles in the insect model Drosophila. Yet much less is known about the physiological properties for NlBRM. In the present study, the cloned full-length cDNA of NlBRM was 5637 bp and contained an ORF of 5292 bp encoding a 194.53 kD protein. The spatiotemporal dynamics of NlBRM was investigated by qPCR, which showed that it was abundantly expressed in the egg and ovary. Then significant downregulation of NlBRM by dsRNA injection had a relatively greater impact on female survival than male. Moreover, the number of oviposition marks of the NlBRM-RNAi females were declined by 61.11% - 73.33% compared with the controls during the subsequent 5 days after dsRNA injection. Meanwhile, the number of newly hatched BPH nymphs also decreased correspondingly by 93.56% - 100%. Phenotypic analysis revealed that none of normally banana-shaped eggs were discernable in the ovaries of NlBRM-deficient females, where mRNA expression of N. lugens vitellogenin gene was also reduced. Our results demonstrated that NlBRM played a crucial role in ovarian development and fecundity of BPH, likely by regulating the vitellogenin gene in vivo, which could be as a promising target for parental RNAi-based control of this serious rice pest.

Phase III randomized study of second line ADI-PEG 20 plus best supportive care versus placebo plus best supportive care in patients with advanced hepatocellular carcinoma

Background

Arginine depletion is a putative target in hepatocellular carcinoma (HCC). HCC often lacks argininosuccinate synthetase, a citrulline to arginine-repleting enzyme. ADI-PEG 20 is a cloned arginine degrading enzyme-arginine deiminase-conjugated with polyethylene glycol. The goal of this study was to evaluate this agent as a potential novel therapeutic for HCC after first line systemic therapy.

Methods and patients

Patients with histologically proven advanced HCC and Child-Pugh up to B7 with prior systemic therapy, were randomized 2 : 1 to ADI-PEG 20 18 mg/m2 versus placebo intramuscular injection weekly. The primary end point was overall survival (OS), with 93% power to detect a 4-5.6 months increase in median OS (one-sided α = 0.025). Secondary end points included progression-free survival, safety, and arginine correlatives.

Results

A total of 635 patients were enrolled: median age 61, 82% male, 60% Asian, 52% hepatitis B, 26% hepatitis C, 76% stage IV, 91% Child-Pugh A, 70% progressed on sorafenib and 16% were intolerant. Median OS was 7.8 months for ADI-PEG 20 versus 7.4 for placebo (P = 0.88, HR = 1.02) and median progression-free survival 2.6 months versus 2.6 (P = 0.07, HR = 1.17). Grade 3 fatigue and decreased appetite occurred in <5% of patients. Two patients on ADI-PEG 20 had ≥grade 3 anaphylactic reaction. Death rate within 30 days of end of treatment was 15.2% on ADI-PEG 20 versus 10.4% on placebo, none related to therapy. Post hoc analyses of arginine assessment at 4, 8, 12 and 16 weeks, demonstrated a trend of improved OS for those with more prolonged arginine depletion.

Conclusion

ADI-PEG 20 monotherapy did not demonstrate an OS benefit in second line setting for HCC. It was well tolerated. Strategies to enhance prolonged arginine depletion and synergize the effect of ADI-PEG 20 are underway.

Clinical Trial number

www.clinicaltrials.gov (NCT 01287585).

Molecular Characterization of Ca2+/Calmodulin-Dependent Protein Kinase II Isoforms in Three Rice Planthoppers-Nilaparvata lugens, Laodelphax striatellus, and Sogatella furcifera

This study reports the identification of splice variants for the calcium/calmodulin-dependent protein kinase II (CaMKII) gene from Nilaparvata lugens, Laodelphax striatellus, and Sogatella furcifera. CaMKII is a multifunctional serine/threonine protein kinase that transduces Ca²⁺ signals in cells to control a range of cellular processes in the nervous system and muscular tissue. Sequence analysis showed that CaMKII was 99.0% identical at the amino acid level among three rice planthoppers, with the exception of a variable region located in the association domain. Four kinds of 20–81 amino acid “inserts” were found in the variable region. The phylogenetic tree of the deduced amino acid sequences showed that the NlCaMKII isoforms were more closely related to the LsCaMKII isoforms and were slightly distinct from SfCaMKII. CaMKII-E was the dominant type among the five main isoforms. CaMKII genes were constitutively expressed in various nymphal and adult stages and in tested tissues with the predominant transcription occurring in the head. There was no major tissue specificity of isoform expression, but the expression pattern and relative abundance of isoforms varied when compared with the RT-PCR between tissues. In addition, RNAi in N. lugens with dsRNA at a concentration of 200 ng nymph⁻¹ induced a mortality of 77.7% on the 10th day and a reduction in the mRNA expression level of 67.2%. Unlike the holometabolous insect Helicoverpa armigera, the knockdown of NlCaMKII did not suppress the expression of 20E response genes, such as ECR, USP1, and HR3, in N. lugens. These results indicate that the role of CaMKII in hemimetabolous insects may be different from that in holometabolous insects.

Identification of Cuticular Protein Genes in the Colorado Potato Beetle Leptinotarsa decemlineata (Coleoptera: Chrysomelidae)

Structural cuticular proteins (CPs) are the primary components of insect cuticle, linings of salivary gland, foregut, hindgut and tracheae, and midgut peritrophic membrane. Variation of CPs in insect cuticle can cause penetration resistance to insecticides. Moreover, depletion of specific CP by RNA interference may be a suitable way for the development of potential pest control traits. Leptinotarsa decemlineata (Say) CPs are poorly characterized at present, and therefore, we mined the genome and transcriptome data to better annotate and classify L. decemlineata CPs in this study, by comparison with the annotated CPs of Tribolium castaneum Browse (Coleoptera: Tenebrionidae). We identified 175 CP genes. Except one miscellaneous CP with an 18-amino acid motif, these CPs were classified into 7 families based on motifs and phylogenetic analyses (CPs with a Rebers and Riddiford motif, CPR; CPs analogous to peritrophins, CPAP3 and CPAP1; CPs with a tweedle motif, TWDL; CPs with a 44-amino acid motif, CPF; CPs that are CPF-like, CPFL; and CPs with two to three copies of C-X5-C motif, CPCFC). Leptinotarsa decemlineata CPRs could be categorized into three subfamilies: RR-1 (50), RR-2 (85), and RR-3 (2). The RR-1 proteins had an additional motif with a conserved YTADENGF sequence. The RR-2 members possessed a conserved RDGDVVKG region and three copes of G-x(3)-VV. Few genes were found in TWDL (9), CPAP1 (9), CPAP3 (8), CPF (5), CPFL (4), and CPCFC (2) families. The findings provide valuable information to explore molecular modes of penetration resistance to insecticides and to develop dsRNA-based control method in L. decemlineata.

Differential Responses of OsMPKs in IR56 Rice to Two BPH Populations of Different Virulence Levels

The conserved mitogen-activated protein kinase (MAPK) cascades play vital roles in plant defense responses against pathogens and insects. In the current study, the expression profiles of 17 OsMPKs were determined in the TN1 and IR56 rice varieties under the infestation of brown planthopper (BPH), one of the most destructive hemimetabolous rice pests. The virulent IR56 BPH population (IR56-BPH) and the avirulent TN1 BPH population (TN-BPH) were used to reveal the roles of OsMPKs in the compatible (IR56-BPH infested on the TN1 and IR56 rice varieties, and TN1-BPH infested on the TN1 rice variety) and the incompatible (TN1-BPH infested on the IR56 rice variety) interaction. The statistical analysis revealed that rice variety, BPH population type, and infestation period have significant effects on the transcription of OsMPKs. Out of these genes, five OsMPKs (OsMPK1, OsMPK3, OsMPK7, OsMPK14, and OsMPK16) were found to exhibit upregulated expression only during incompatible interaction. Six OsMPKs (OsMPK4, OsMPK5, OsMPK8, OsMPK9, OsMPK12, and OsMPK13) were associated with both incompatible and compatible interactions. The transcription analysis of salicylic acid, jasmonic acid, and ethylene phytohormone signaling genes revealed their roles during the rice⁻BPH interactions. The upregulated expression of OsC4H, OsCHS, and OsCHI in the incompatible interaction implied the potential defense regulatory roles of phenylpropanoids. In both varieties, the elevated transcript accumulations of OsGST and OsSOD, and the increased enzyme activities of POD, SOD, and GST at 1 day post-infestation (dpi), but not at 3 dpi, indicated that reactive oxygen species (ROS) signaling might be an early event in rice⁻BPH interactions. Furthermore, upregulated transcription of OsLecRK3 and OsLecRK4 was found only during an incompatible interaction, suggesting their involvement in the BPH resistance response in the IR56 rice variety. Lastly, based on the findings of this study, we have proposed a model of interactions of IR56 rice with TN1-BPH and IR56-BPH that depicts the resistance and susceptibility reactions, respectively.

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.

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.

Identification of glutathione S-transferase genes in Leptinotarsa decemlineata and their expression patterns under stress of three insecticides

Glutathione S-transferases (GSTs) is a family of multifunctional enzymes that are involved in detoxification of poisonous compounds. In the present paper, the Leptinotarsa decemlineata genome and transcriptome dataset were mined and 30 GST genes were identified. These GSTs belonged to cytosolic (29 genes) and microsomal (1 gene) classes. Among them 3 GSTs (LdGSTe2, LdGSTs4, and LdGSTo3) possessed splice variants. Of the 29 cytosolic LdGSTs, 3, 10, 5, 4, 4, and 1 members were classified as delta, epsilon, omega, sigma, theta, and zeta subclasses respectively, along with 2 unclassified genes. Phylogenetic analysis suggest that epsilon, omega and sigma subclasses appear to undergo species-specific bloom. Moreover, most epsilon, omega and sigma GSTs are tandemly arranged in three chromosome scaffolds. To find GST candidates involving in insecticide detoxification, we tested the mRNA levels of 20 GST transcripts under stress of cyhalothrin, fipronil or endosulfan. Out of them, LdGSTe2a, LdGSTe2b, LdGSTo5 and LdGSTt1 were significantly overexpressed after exposure to each of the three insecticides. Two other genes were respectively upregulated after cyhalothrin (LdGSTe10 and LdGSTu2) or endosulfan (LdGSTd1 and LdGSTu2) treatment. The diversified expression responses to insecticide exposure suggest that the LdGSTs may depend on a functionally complex system to detoxify different classes of insecticides. In addition, our findings provide a base for a better understanding of the evolution of insecticide resistance, and functional research on specific GST genes.

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.

Molecular cloning and characterization of the putative Halloween gene Phantom from the small brown planthopper Laodelphax striatellus

Ecdysteroid hormone 20-hydroxyecdysone plays fundamental roles in insect postembryonic development and reproduction. Several cytochrome P450 mono-oxygenases (CYPs), encoded by the Halloween genes, have been documented to be involved in ecdysteroidogenesis in representative insects in Diptera, Lepidoptera and Orthoptera. Here the putative Halloween gene Phantom (Phm, cyp306a1) from a hemipteran insect species, the small brown planthopper Laodelphax striatellus, was cloned. LsPHM shows five insect conserved P450 motifs, that is, Helix-C, Helix-I, Helix-K, PERF and heme-binding motifs. Temporal and spatial expression patterns of LsPhm were evaluated by quantitative polymerase chain reaction. Through the fourth-instar and the early fifth-instar stages, LsPhm showed two expression peaks in day 2 and days 4-5 fourth-instar nymphs, and three troughs in day 1 and 3 fourth instars and day 1 fifth instars. On day 5 of the fourth-instar nymphs, LsPhm clearly had a high transcript level in the thorax where the prothoracic glands were located. Dietary introduction of double-stranded RNA (dsRNA) of LsPhm at the nymph stage successfully knocked down the target gene, decreased expression level of ecdysone receptor (LsEcR) gene and caused a higher nymphal mortality rate and delayed development. Ingestion of 20-hydroxyecdysone on LsPhm-dsRNA-exposed nymphs did not increase LsPhm expression level, but almost completely rescued the LsEcR mRNA level, and relieved the negative effects on survival and development. Thus, our data suggest that the putative LsPhm encodes a functional 25-hydroxylase that catalyzes the biosynthesis of ecdysteroids in L. striatellus.

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.

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.

RNA interference-mediated silencing of a Halloween gene spookier affects nymph performance in the small brown planthopper Laodelphax striatellus

Post-embryonic development of insects is highly dependent on ecdysteroid hormone 20-hydroxyecdysone. Halloween gene spookier (spok, cyp307a2) has been documented to be involved in ecdysteroidogenesis in Drosophila melanogaster and Bombyx mori. We describe here the cloning and characterization of Halloween gene spookier (Lsspok, Lscyp307a2) in the small brown planthopper Laodelphax striatellus, a hemipteran insect species. LsSPOK has three insect-conserved P450 motifs, that is, Helix-K, PERF motif and heme-binding domain. Temporal and spatial expression patterns of Lsspok were evaluated by quantitative polymerase chain reaction. Through the fouth-instar and the early fifth-instar stages, Lsspok showed two expression peaks in the second- and fifth-day fourth-instar nymphs, and two troughs in the first-day fourth and fifth instars. On day 5 of the fourth-instar nymphs, Lsspok clearly had a high transcript level in the thorax where prothoracic glands were located. Dietary introduction of double-stranded RNA of Lsspok in the nymph stage successfully knocked down the target gene, decreased expression level of ecdysone receptor (LsEcR) gene, caused nymphal lethality and delayed development. Ingestion of 20-hydroxyecdysone in Lsspok-dsRNA-exposed nymphs did not increase Lsspok expression level, but almost completely rescued the LsEcR mRNA level and relieved the negative effects on survival and development. Thus, our data suggest that the ecdysteroidogenic pathway is conserved in insects and LsSPOK is responsible for specific steps in ecdysteroidogenesis in L. striatellus.

A Halloween gene shadow is a potential target for RNA-interference-based pest management in the small brown planthopper Laodelphax striatellus

BACKGROUND

Laodelphax striatellus is an economically important rice pest in China. Ecdysteroid hormone 20-hydroxyecdysone regulates insect development and reproduction. The cytochrome P450 monooxygenase Shadow (Sad) plays a critical role in ecdysteroidogenesis. Here, tests were conducted to establish whether Lssad was a potential target gene for RNA-interference-based management of L. striatellus.

RESULTS

Lssad was cloned and characterised. LsSad had Helix-C, Helix-I, Helix-K, PERF and haem-binding motifs. Lssad is expressed at a higher level in the thorax, where prothoracic glands are located, compared with the level in the head or abdomen. It showed two expression peaks in day 2 and day 4-5 fourth-instar nymphs, and two troughs in day 1 fourth and fifth instars. Oral delivery of double-stranded RNA (dsRNA) of Lssad at the nymph stage successfully knocked down the expression of the target gene, reduced the expression level of ecdysone receptor (LsEcR) gene, caused nymphal lethality and delayed development in a dose-dependent manner. Ingestion of 20-hydroxyecdysone in Lssad-dsRNA-exposed nymphs did not increase Lssad expression level, but almost completely rescued the LsEcR mRNA level and relieved the negative effects on survival and development.

CONCLUSIONS

The ecdysteroidogenic pathway is conserved in L. striatellus. Lssad can serve as a possible target for dsRNA-based pesticides for planthopper control.

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.

The putative Halloween gene phantom involved in ecdysteroidogenesis in the white-backed planthopper Sogatella furcifera

Postembryonic development of insects is highly dependent on ecdysteroid hormones ecdysone (E) and 20-hydroxyecdysone (20E). A cytochrome P450 monooxygenase CYP306A1, the product of the Halloween gene phantom (phm), is involved in the ecdysteroidogenesis in representative insects in Diptera, Lepidoptera and Orthoptera. In the present paper, Sfphm was cloned from a hemipteran insect species, the white-backed planthopper Sogatella furcifera. SfPHM has five insect conserved P450 motifs, i.e., Helix-C, Helix-I, Helix-K, PERF and heme-binding motifs. Temporal and spatial expression patterns of Sfphm were evaluated by q-PCR. Sfphm showed three expression peaks in late second-, third- and fourth-instar stages. In contrast, the expression levels were lower and formed three troughs in the newly-molted second-, third- and fourth-instar nymphs. The relative 20E levels exhibited similar temporal patterns to Sfphm expression levels. On day 3 of the fourth-instar nymphs, Sfphm clearly had a high transcript level in the thorax where PGs were located. Dietary introduction of double-stranded RNA of Sfphm into the second instars successfully knocked down the target gene, and greatly reduced 20E level and ecdysone receptor (EcR) expression level. Moreover, knockdown of Sfphm caused lethality and slowed down ecdysis during nymphal stages. Furthermore, ingestion of 20-hydroxyecdysone did not alter Sfphm expression level, but almost completely rescued SfEcR expression level, and relieved the negative effects on nymphal survival and ecdysis in Sfphm-dsRNA-exposed planthoppers. Thus, our results suggest that Sfphm plays a critical role in ecdysteroidogenesis in S. furcifera.

RNAi suppression of the ryanodine receptor gene results in decreased susceptibility to chlorantraniliprole in Colorado potato beetle Leptinotarsa decemlineata

Leptinotarsadecemlineata is the most important pest in potato and causes serious yield loss each year. Chlorantraniliprole acts on insect ryanodine receptors (RyRs) and is among the most active compounds against L. decemlineata. Here we cloned and characterized a 15,792-bp full-length LdRyR cDNA that encoded a 5128-amino acid protein. LdRyR shares 85-92% amino acid similarities with other insect RyR homologues, and 59-61% similarities with those from Caenorhabditis elegans and Homo sapiens. All hallmarks of the RyR proteins are conserved in LdRyR. LdRyR has a MIR domain, two RIH domains, three SPRY domains, four copies of RyR domain and a RIH-associated domain in the N-terminus, and it possesses two consensus calcium ion-binding EF-hand motifs and six predicted transmembrane helices in the C-terminus. Temporal, spatial and tissue-specific expression patterns of LdRyR were evaluated. LdRyR expression level was increased constantly from egg to wandering stages, dropped in pupal stage and was increased again in the adult stage. It was widely expressed in the head, thorax and abdomen of day 3 fourth-instar larvae. Moreover, it was ubiquitously expressed in all inspected tissues including epidermis, foregut, midgut, ileum, rectum, fat body, ventral ganglia and Malpighian tubules in day 3 fourth-instar larvae. Dietary introduction of double-stranded RNA of LdRyR significantly reduced the mRNA levels of the target gene in the larvae and adults, respectively, and significantly decreased chlorantraniliprole-induced mortalities. Thus, our results suggested that LdRyR encoded a functional ryanodine receptor in L. decemlineata.

Molecular cloning and characterization of a putative proline dehydrogenase gene in the Colorado potato beetle, Leptinotarsa decemlineata

Leptinotarsa decemlineata adults exhibit a season-dependent activity. In spring, post-diapause beetles often fly a long distance from overwintering sites to potato fields. In summer and autumn, the flight ability is sharply reduced. Proline is the main energy substrate of L. decemlineata during flight and proline dehydrogenase (ProDH) catalyzes the first step in proline catabolism. Here we identified a putative LdProDH gene; it had three cDNA isoforms which shared the same 5'UTR and coding region, but differed in the lengths of 3'UTRs (515, 1 092 and 1 242 bp for isoforms-1, -2 and -3, respectively). LdProDH encoded a 616 amino acid protein that showed high sequence similarity to ProDH-like proteins from other insect species. LdProDH was expressed in the third and fourth instars larvae and adults, but not in pupae. Dietary ingestion of bacterially expressed LdProDH-dsRNA by adults significantly decreased its messenger RNA (mRNA) level, and caused an elevation of free proline content in the hemolymph. Further observation revealed that three canonical polyadenylation signals (AATAAA) were tandemly located in the 3'UTR of isoform-3. The first, second and third polyadenylation sites gave rise to isoforms-1, -2 and -3, respectively. Analysis of the genomic DNA uncovered that the three isoforms resulted from alternative polyadenylation. The mRNA level of isoform-1, which expressed at low levels in pre-diapause adults, became abundant in post-diapause beetles. It is indicated that the LdProDH expression is fine-tuned through 3'UTR to control proline catabolism for the season-dependent activity of L. decemlineata adults.

Characterization of cysteine protease-like genes in the striped rice stem borer, Chilo suppressalis

The striped rice stem borer, Chilo suppressalis (Walker), is a major pest for rice production in China and the rest of Southeast Asia. Chemical control is the main means to alleviate losses due to this pest, which causes serious environmental pollution. An effective and environmentally friendly approach is needed for the management of the striped rice stem borer. Cysteine proteases in insects could be useful targets for pest management either through engineering plant protease inhibitors, targeting insect digestive cysteine proteases, or through RNA interference-based silencing of cysteine proteases, disrupting developmental regulation of insects. In this study, eight cysteine protease-like genes were identified and partially characterized. The genes CCO2 and CCL4 were exclusively expressed in the larval gut, and their expression was affected by the state of nutrition in the insect. The expression of CCL2, CCL3, and CCO1 was significantly affected by the type of host plant, suggesting a role in host plant – insect interactions. Our initial characterization of the striped rice stem borer cysteine protease-like genes provides a foundation for further research on this important group of genes in this major insect pest of rice.

RNAi mediated knockdown of the ryanodine receptor gene decreases chlorantraniliprole susceptibility in Sogatella furcifera

The diamide insecticides activate ryanodine receptors (RyRs) to release and deplete intracellular calcium stores from the sarcoplasmic reticulum of muscles and the endoplasmic reticulum of many types of cells. They rapidly interrupt feeding of the target pest and eventually kill the pest due to starvation. However, information about the structure and function of insect RyRs is still limited. In this study, we isolated a 15,985bp full-length cDNA (named SfRyR) from Sogatella furcifera, a serious rice planthopper pest throughout Asia. SfRyR encodes a 5140-amino acid protein, which shares 78-97% sequence identities with other insect homologues, and less than 50% identities with Homo sapiens RyR1-3. All hallmarks of the RyR proteins are conserved in SfRyR. In the N-terminus, SfRyR has a MIR domain, two RIH domains, three SPRY domains, four copies of RyR repeated domain and a RIH-associated domain. In the C-terminus, SfRyR possesses two consensus calcium ion-binding EF-hand motifs, and six transmembrane helices. Temporal and spatial expression analysis showed that SfRyR was widely found in all development stages including egg, first through fifth instar nymphs, macropterous adult females and males. On day 2 fifth-instar nymphs, SfRyR was ubiquitously expressed in the head, thorax and abdomen. Dietary ingestion of dsSfRyR1 and dsSfRyR2 significantly reduced the mRNA level of SfRyR in the treated nymphs by 77.9% and 81.8% respectively, and greatly decreased chlorantraniliprole-induced mortality. Thus, our results suggested that SfRyR gene encoded a functional RyR that mediates chlorantraniliprole toxicity to S. furcifera.

Identification of cytochrome P450 monooxygenase genes and their expression profiles in cyhalothrin-treated Colorado potato beetle, Leptinotarsa decemlineata

Based on a Leptinotarsa decemlineata transcriptome dataset and the GenBank sequences, a total of 74 cytochrome P450 monooxygenase genes (Cyps) were identified. These genes fell into CYP2 clan, mitochondrial clan, CYP3 clan and CYP4 clan, and were classified into 19 families and 35 subfamilies according to standard nomenclature. Two new families were discovered in CYP4 clan, and were named CYP412 and CYP413 respectively. Four new families that were recently discovered in Tribolium castaneum, including mitochondrial family CYP353, CYP3 clan families CYP345 and CYP347, and CYP4 clan family CYP350, were also found in L. decemlineata. The phylogenetic trees of CYPs from L. decemlineata and other representative insect species were constructed, and these trees provided evolutionary insight for the genetic distance. Our results facilitate further researches to understand the functions and evolution of L. decemlineata Cyp genes. In order to find cyhalothrin-inducible Cyp genes, the expression levels of Cyps belonging to CYP12, CYP6, CYP9 and CYP4 families were determined by quantitative reverse transcriptase-PCR in cyhalothrin-treated and control fourth-instar larvae. Nine Cyp genes, i.e., Cyp12H2, Cyp6BH2, Cyp6BJ1, Cyp6BQ17, Cyp6EG1, Cyp6EH1, Cyp6EJ1 Cyp4BN13v1 and Cyp4BN15, were highly expressed in cyhalothrin-treated larvae. These CYPs are the candidates that are involved in cyhalothrin detoxification.

RNA interference of a putative S-adenosyl-L-homocysteine hydrolase gene affects larval performance in Leptinotarsa decemlineata (Say)

In Leptinotarsa decemlineata, juvenile hormones (JHs) play primary roles in the regulation of metamorphosis, reproduction and diapause. In JH biosynthetic pathway in insect corpora allata, methylation of farnesoic acid or JH acid using S-adenosyl-L-methionine generates a potent feedback inhibitor S-adenosyl-L-homocysteine (AdoHcy). Rapid removal of AdoHcy is hypothesized to be essential for JH synthesis. AdoHcy hydrolase (SAHase) is the only eukaryotic enzyme catalyzing the removal. In the present paper, we firstly cloned a putative LdSAHase gene from L. decemlineata. The cDNA consists of 1806 bp and encodes a 525 amino acid protein. LdSAHase was expressed in all developmental stages. The gene had the highest and the lowest level of transcription respectively in the 3rd- and 4th-instars' heads that contain corpora allata, which was positively correlated with JH titer in the haemolymph and the mRNA level of a JH early-inducible gene, the Krüppel homolog 1 gene (Kr-h1). Secondly, dietary ingestion of bacterially-expressed LdSAHase-dsRNA significantly decreased LdSAHase and LdKr-h1 mRNA levels, reduced JH titer, and caused the death of the larvae, and the failure of pupation and adult emergence. After continuous exposure for 12 days, 42% of the larvae died, 65% of the prepupae failed to pupate and 100% of the pupae failed to emerge. Moreover, RNAi-mediated LdSAHase knockdown also reduced larval developing time, and decreased larval weight. Lastly, application of JH analogue pyriproxyfen to LdSAHase-dsRNA-exposed larvae did not greatly increase LdSAHase expression level and JH content, but up-regulated LdKr-h1 mRNA level. Expectedly, pyriproxyfen application could partially rescue the negative effects on the survival and the development. Thus, our results support the hypothesis that SAHase plays a critical role in JH biosynthesis in insects.

Molecular cloning and RNA interference-mediated functional characterization of a Halloween gene spook in the white-backed planthopper Sogatella furcifera

Background

Ecdysteroid hormones ecdysone and 20-hydroxyecdysone play fundamental roles in insect postembryonic development and reproduction. Five cytochrome P450 monooxygenases (CYPs), encoded by Halloween genes, have been documented to be involved in the ecdysteroidogenesis in insect species of diverse orders such as Diptera, Lepidoptera and Orthoptera. Up to now, however, the involvement of the Halloween genes in ecdysteroid synthesis has not been confirmed in hemipteran insect species.

Results

In the present paper, a Halloween gene spook (Sfspo, Sfcyp307a1) was cloned in the hemipteran Sogatella furcifera. SfSPO has three insect conserved P450 motifs, i.e., Helix-K, PERF and heme-binding motifs. Temporal and spatial expression patterns of Sfspo were evaluated by qPCR. Sfspo showed three expression peaks in late second-, third- and fourth-instar stages. In contrast, the expression levels were lower and formed three troughs in the newly-molted second-, third- and fourth-instar nymphs. On day 3 of the fourth-instar nymphs, Sfspo clearly had a high transcript level in the thorax where PGs were located. Dietary introduction of double-stranded RNA (dsRNA) of Sfspo into the second instars successfully knocked down the target gene, and greatly reduced expression level of ecdysone receptor (EcR) gene. Moreover, knockdown of Sfspo caused lethality and delayed development during nymphal stages. Furthermore, application of 20-hydroxyecdysone on Sfspo-dsRNA-exposed nymphs did not increase Sfspo expression, but could almost completely rescue SfEcR expression, and relieved the negative effects on nymphal survival and development.

Conclusion

In S. furcifera, Sfspo was cloned and the conservation of SfSPO is valid. Thus, SfSPO is probably also involved in ecdysteroidogenesis for hemiptera.

Cloning and characterization of serpin-like genes from the striped rice stem borer, Chilo suppressalis

Serpins, also called serine proteinase inhibitors, are widely distributed in eukaryotes. In insects, serpins play important roles in regulating immune responses, gut physiology, and other processes. Here, we report the cloning and characterization of 12 serpin-like cDNAs from the striped rice stem borer (Chilo suppressalis), a major rice pest. The putative proteins share significant sequence similarity with known insect serpins, especially those from lepidopterons. Analysis of functional domains revealed that nine of the cloned serpins are putative trypsin- or chymotrypsin-like inhibitors; two are mixed-type serpins that may act as inhibitors for trypsins, elastases, or thrombin; and the remaining one is truncate. The potential functions of these serpins in interacting with host plants were also investigated by analyzing tissue-specific expression and the impact of different host plant genotypes on gene expression. Our results provide a foundation for future studies on the role of serpins in gut physiology in the striped rice stem borer, and also useful information for comparative analyses of serpins from different insect species.

Bacillus thuringiensis insecticidal crystal proteins affect lifespan and reproductive performance of Helicoverpa armigera and Spodoptera exigua adults

Being delivered as sprays or expressed in plant, Bacillus thuringiensis (Bt) crystalline proteins (Cry toxins) display insecticidal activities against numerous Lepidopteran, Dipteran, and Coleopteran larvae. Comparative study of toxicities of Bt Cry toxins between larvae and adults may afford important new insights into the interactions of the toxins with receptor proteins in host insect, and represent intriguing targets for the control of insect pests. However, the effectiveness of Bt Cry toxins in insect adults has paid less attention. In the present article, the effectiveness of Cry1Ac and Cry1Ca on lifespans and reproductive performance of Helicoverpa armigera (Hübner) and Spodoptera exigua (Hübner) adults were evaluated by in vivo experiments. Considering transgenic plants express modified, truncated versions of cry genes yielding active toxin fragment, we used activated Bt toxins at the concentration of 500, 100, and 20 microg/ml in a 10% sucrose aquous solution. At the highest concentration, Cry1Ac and Cry1Ca shortened 48.1 and 48.9% of H. armigera female lifespan, and 43.5 and 38.5% of S. exigua female lifespan, and they reduced 37.8 and 40.3%, and 50.5 and 47.4% of H. armigera and S. exigua male lifespans respectively. Bt toxins negatively affected copulation. Exposure to 500 microg/ml of Cry1Ac and Cry1Ca greatly reduced 50.0 and 46.8%, and 58.7 and 57.3% spermatophore acceptance by H. armigera and S. exigua females, respectively. Similarly, Cry1Ac and Cry1Ca exposure decreased 40.0 and 50.3%, and 61.3 and 60.0% of spermatophore transfer by H. armigera and S. exigua males, respectively. Moreover, exposure females rather than males to 500 microg/ml of Cry1Ac and Cry1Ca significantly dropped 57.5 and 57.5% of the number of eggs laid by H. armigera, and 35.4 and 45.8% of the number of egg masses deposited by S. exigua. In contrast, both Cry1Ac and Cry1Ca did not negatively influence the egg hatchability. At the middle and the lowest concentrations, however, the biological effects of Cry1Ac and Cry1Ca on lifespans and reproductive performance partially or completely disappeared.

Validation of reference genes for expression analysis by quantitative real-time PCR in Leptinotarsa decemlineata (Say)

Background

L. decemlineata is an exotic invasive insect pest, and invaded in Xinjiang Uygur autonomous region in China in the 1990s from Kazakhstan. It is a notorious defoliator of potato throughout most of the northern Xinjiang in current, and often causes extremely large yield losses of potato.

Results

The expression stability of nine L. decemlineata house-keeping genes (Actin, ACT1 and ACT2; ADP-ribosylation factor, ARF1 and ARF4; TATA box binding protein, TBP1 and TBP2; ribosomal protein RP4 and RP18; translation elongation factor 1α EF1α) was evaluated by quantitative real-time polymerase chain reaction (qRT-PCR) in seven developmental stages, three larval tissues and two insecticide treatments. The results were analyzed using three software programs: geNorm, NormFinder and BestKeeper. Although there was no consistent ranking observed among the house-keeping genes across the samples, the overall analysis revealed that RP18, RP4, ARF1, and ARF4 were the four most stable house-keeping genes. In contrast, ACT1 and ACT2, two of the most widely used reference genes, had the least stability. Our results suggest that the combined use of the four most stably expressed genes may produce optimal normalization for qRT-PCR.

Conclusions

The expression stability of the house-keeping genes varies among different developing stages, in different tissues and under different experimental conditions. Our results will enable a more accurate and reliable normalization of qRT-PCR data in L. decemlineata.

Cloning and characterization of trypsin- and chymotrypsin-like genes in the striped rice stem borer, Chilo suppressalis

Serine proteinases including trypsins and chymotrypsins play various important roles in insects, including food digestion, immune defense, and zymogen activation. Studies on insect serine proteinases could reveal their feeding preference (polyphagous and monophagous) and facilitate identification of protease inhibitors, which can be engineered for pest management. In this paper, 11 transcripts encoding trypsin- and chymotrypsin-like proteins were cloned from the striped rice stem borer, Chilo suppressalis (Walker). All the predicted proteins share high sequence similarity with known trypsin- and chymotrypsin-like proteins from either lepidopterans or dipterans, and most of the proteins have conserved motifs that are characteristics of serine proteinases. Among the 11 cloned genes, six were expressed predominantly and one exclusively in the midgut of the insect, three were expressed relatively evenly in examined tissues, and one was not expressed in either the gut or hemolymph based on RT–PCR results. The seven genes that were predominantly or exclusively expressed in the gut were also affected by feeding on different host plants. The genes that were expressed in the gut and were affected by host plants are likely to encode digestive proteinases. The identification of trypsin- and chymotrypsin-like genes in this insect species is the first step towards further comparative studies and for identification of insect-specific proteinase inhibitors, which might be engineered to protect rice plants against the striped rice stem borer, which is one of the destructive pests of rice.

In vitro inhibitory effect of gossypol from gossypol-acetic acid, and (+)- and (-)-isomers of gossypol on the growth of Edwardsiella ictaluri

AIM

This study was conducted to evaluate the toxic effect of gossypol from gossypol-acetic acid, and (+)- and (-)-isomers of gossypol on the growth of Edwardsiella ictaluri.

METHODS AND RESULTS

Inhibitory effect of various concentrations of gossypol on the growth of E. ictaluri was determined. Bacterial recovery was performed by preincubation of bacteria in medium containing various concentrations of gossypol and subsequent activation of bacteria by inoculating on gossypol-free plates. Concentrations of racemic gossypol, (+)-gossypol and (-)-gossypol of 1.5 microg ml(-1) or higher significantly reduced the number of bacterial colonies compared with that of the control. The growth of E. ictaluri was completely inhibited on agar plates supplemented with 3 microg ml(-1), regardless of the forms of gossypol. The inhibitory effect of (+)-gossypol was higher than that of (-)-gossypol or gossypol-acetic acid. Recovery of E. ictaluri was <50% for all three forms of gossypol at concentrations of 5 microg ml(-1). Bacterial recovery remained relatively constant (6.5%) at gossypol concentrations from 10 to 100 microg ml(-1). Complete killing of E. ictaluri was not reached at gossypol levels up to 100 microg ml(-1).

CONCLUSION

Gossypol-acetic acid, and (+)- and (-)-optical isomers have anti-bacterial effect against E. ictaluri. The results suggest the action is bacteriostatic rather than bactericidal.

SIGNIFICANCE AND IMPACT OF THE STUDY

The therapeutic effect of gossypol against E. ictaluri may be useful in controlling enteric septicaemia of catfish.

Molecular weights and molecular-weight distributions from ultracentrifugation of nonideal solutions

Ultracentrifugation, membrane osmometry and capillary viscometry experiments have been performed on two dextran samples, which have molecular-weight distributions (MWDs) similar to those of dextrans used as blood plasma extenders. The manufacturer reported values of Mn and MW, determined by end group analysis and by light scattering, respectively. Our values of Mn, determined by osmometry, and MW, calculated from ultracentrifugal and viscometry experiments, agreed quite well with the manufacturer's results. Good agreement was obtained with values of MW and BLS (the light scattering second virial coefficient) obtained from sedimentation equilibrium experiments at different speeds using sector or nonsector-shaped centerpieces. Several ways of obtaining MW, MZ and BLS from sedimentation equilibrium experiments are presented. We have also shown how to obtain the speed-dependent term of the sedimentation equilibrium second virial coefficient. Both BLS and the speed-dependent nonideal terms could be used to correct the sedimentation equilibrium data, so that ideal values of d in c/d(r2) or dc/d(r2) could be estimated and used to obtain the MWDs of the dextran samples. Both Donnelly's and Scholte's methods were used with the sedimentation equilibrium data. With both methods, unimodal MWDs were encountered, which gave good agreement with the manufacturer's MWDs, obtained by a combination of analytical gel chromatography and light scattering. Uncorrected sedimentation equilibrium data gave MWDs quite different from the manufacturer's results. The MWD calculated from the differential distribution of sedimentation coefficients also gave a unimodal MWD, but this MWD did not give a good agreement with the sedimentation equilibrium results or with the manufacturer's results.