Molecular characterization, expression analysis and RNAi knock-down of elongation factor 1α and 1γ from Nilaparvata lugens and its yeast-like symbiont

RNAi-Mediated Knockdown of Imaginal Disc Growth Factors (IDGFs) Genes Causes Developmental Malformation and Mortality in Melon Fly, Zeugodacus cucurbitae

This study reports the first successful use of oral feeding dsRNA technique for functional characterization of imaginal disc growth factors (IDGFs) genes (IDGF1, IDGF3_1, IDGF4_0, IDGF4_1, and IDGF6) in melon fly Zeugodacus cucurbitae. Phylogenetic and domain analysis indicates that these genes had high similarity with other Tephritidae fruit flies homolog and contain only one conserved domain among these five genes, which is glyco-18 domain (glyco-hydro-18 domain). Gene expression analysis at different developmental stages revealed that these genes were expressed at larval, pupal, and adult stages. To understand their role in different developmental stages, larvae were fed dsRNA-corresponding to each of the five IDGFs, in an artificial diet. RNAi-mediated knockdown of IDGF1 shows no phenotypic effects but caused mortality (10.4%), while IDGF4_0 caused malformed pharate at the adult stage where insects failed to shed their old cuticle and remained attached with their body, highest mortality (49.2%) was recorded compared to dsRNA-green fluorescent protein (GFP) or DEPC. Silencing of IDGF3_1 and IDGF4_1 cause lethal phenotype in larvae, (17.2%) and (40%) mortality was indexed in Z. cucurbitae. IDGF6 was mainly expressed in pupae and adult stages, and its silencing caused a malformation in adult wings. The developmental defects such as malformation in wings, larval–larval lethality, pupal–adult malformation, and small body size show that IDGFs are key developmental genes in the melon fly. Our results provide a baseline for the melon fly management and understanding of IDGFs specific functions in Z. cucurbitae.

Knockdown of AMP-activated protein kinase increases the insecticidal efficiency of pymetrozine to Nilaparvata lugens

Insecticides are the main tools used to control Nilaparvata lugens (Stål), a serious pest of rice in Asia. However, repeated application of insecticides has caused many negative effects. Reducing the amount of insecticide used, while maintaining good pest population control, would be valuable. AMP-activated protein kinase (AMPK), a sensor of cellular energy status, helps to maintain insect energy balance at the cellular and whole-body level. The role of AMPK in insect response to insecticide stimulation is unknown. We studied the functions of AMPK catalytic subunit alpha (NlAMPKα) in the development of N. lugens and in response to pymetrozine, an insecticide used to control insect pests with piercing-sucking mouthparts. A phylogenetic analysis of protein sequences from 12 species in six orders showed that insects have only the AMPKα 2 subtype. RNA interference against NlAMPKα demonstrated that blocking the AMPK pathway led to a decrease in the systemic ATP level and an increase in N. lugens mortality. NlAMPKα responded to the energy stress caused by pymetrozine treatment, which activated downstream energy metabolic pathways to compensate for the energy imbalance. However, the ATP level in pymetrozine- treated nymphs was not increased, suggesting that ATP is consumed more than synthesized. When NlAMPKα expression was reduced in pymetrozine-treated nymphs by RNAi, the ATP level was decreased and the mortality was significantly increased. At day eight post 0.5 g/3 L of pymetrozine and dsNlAMPKα treatment, nymph survival was 29.33%, which was similar to the 27.33% survival of 1 g/3 L pymetrozine-treated nymphs. Addition of dsNlAMPKα can reduce the concentration of pymetrozine used by 50% while providing comparable efficacy. These results indicate that AMPK helps maintain the energy metabolism of N. lugens in response to pymetrozine treatment. Knockdown of NlAMPKα increases the insecticidal efficiency of pymetrozine to N. lugens.

Identification and evaluation of reference genes for quantitative real-time PCR analysis in Polygonum cuspidatum based on transcriptome data

BACKGROUND

Polygonum cuspidatum of the Polygonaceae family is a traditional medicinal plant with many bioactive compounds that play important roles in human health and stress responses. Research has attempted to identify biosynthesis genes and metabolic pathways in this species, and quantitative real-time PCR (RT-qPCR) has commonly been used to detect gene expression because of its speed, sensitivity, and specificity. However, no P. cuspidatum reference genes have been identified, which hinders gene expression studies. Here, we aimed to identify suitable reference genes for accurate and reliable normalization of P. cuspidatum RT-qPCR data.

RESULTS

Twelve candidate reference genes, including nine common (ACT, TUA, TUB, GAPDH, EF-1γ, UBQ, UBC, 60SrRNA, and eIF6A) and three novel (SKD1, YLS8, and NDUFA13), were analyzed in different tissues (root, stem, and leaf) without treatment and in leaves under abiotic stresses (salt, ultraviolet [UV], cold, heat, and drought) and hormone stimuli (abscisic acid [ABA], ethylene [ETH], gibberellin [GA₃], methyl jasmonate [MeJA], and salicylic acid [SA]). Expression stability in 65 samples was calculated using the △CT method, geNorm, NormFinder, BestKeeper, and RefFinder. Two reference genes (NDUFA13 and EF-1γ) were sufficient to normalize gene expression across all sample sets. They were also the two most stable genes for abiotic stresses and different tissues, whereas NDUFA13 and SKD1 were the top two choices for hormone stimuli. Considering individual experimental sets, GAPDH was the top-ranked gene under ABA, ETH, and GA₃ treatments, while 60SrRNA showed good stability under MeJA and cold treatments. ACT, UBC, and TUB were suitable genes for drought, UV, and ABA treatments, respectively. TUA was not suitable because of its considerable variation in expression under different conditions. The expression patterns of PcPAL, PcSTS, and PcMYB4 under UV and SA treatments and in different tissues normalized by stable and unstable reference genes demonstrated the suitability of the optimal reference genes.

CONCLUSIONS

We propose NDUFA13 and EF-1γ as reference genes to normalize P. cuspidatum expression data. To our knowledge, this is the first systematic study of reference genes in P. cuspidatum which could help advance molecular biology research in P. cuspidatum and allied species.

Regulatory functions of trehalose-6-phosphate synthase in the chitin biosynthesis pathway in Tribolium castaneum (Coleoptera: Tenebrionidae) revealed by RNA interference

RNA interference (RNAi) is a very effective technique for studying gene function and may be an efficient method for controlling pests. Trehalose-6-phosphate synthase (TPS), which plays a key role in the synthesis of trehalose and insect development, was cloned in Tribolium castaneum (Herbst) (TcTPS) and the putative functions were studied using RNAi via the injection of double-stranded RNA (dsRNA) corresponding to conserved TPS and trehalose-6-phosphate phosphatase domains. Expression analyses show that TcTPS is expressed higher in the fat body, while quantitative real-time polymerase chain reaction results show that the expression of four trehalase isoforms was significantly suppressed by dsTPS injection. Additionally, the expression of six chitin synthesis-related genes, such as hexokinase 2 and glutamine-fructose-6-phosphate aminotransferase, was suppressed at 48 and 72 h post-dsTPS-1 and dsTPS-2 RNA injection, which were two dsTPS fragments that had been designed for two different locations in TcTPS open reading frame, and that trehalose content and trehalase 1 activity decreased significantly at 72 h post-dsRNA injection. Furthermore, T. castaneum injected with dsTPS-1 and dsTPS-2 RNA displayed significantly lower levels of chitin and could not complete the molting process from larvae to pupae, revealing abnormal molting phenotypes. These results demonstrate that silencing TPS gene leads to molting deformities and high mortality rates via regulation of gene expression in the chitin biosynthetic pathway, and may be a promising approach for pest control in the future.

Culture degeneration in conidia of Beauveria bassiana and virulence determinants by proteomics

The quality of Beauveria bassiana conidia directly affects the virulence against insects. In this study, continuous subculturing of B. bassiana on both rice grains and potato dextrose agar (PDA) resulted in 55 and 49 % conidial yield reduction after 12 passages and 68 and 60 % virulence reduction after 20 and 12 passages at four d post-inoculation, respectively. The passage through Tenebrio molitor and Spodoptera exigua restored the virulence of rice and PDA subcultures, respectively. To explore the molecular mechanisms underlying the conidial quality and the decline of virulence after multiple subculturing, we investigated the conidial proteomic changes. Successive subculturing markedly increased the protein levels in oxidative stress response, autophagy, amino acid homeostasis, and apoptosis, but decreased the protein levels in DNA repair, ribosome biogenesis, energy metabolism, and virulence. The nitro blue tetrazolium assay verified that the late subculture's colony and conidia had a higher oxidative stress level than the early subculture. A 2A-type protein phosphatase and a Pleckstrin homology domain protein Slm1, effector proteins of the target of rapamycin (TOR) complex 1 and 2, respectively, were dramatically increased in the late subculture. These results suggest that TOR signalling might be associated with ageing in B. bassiana late subculture, in turn affecting its physiological characteristics and virulence.