ABSTRACT
Reverse-transcription quantitative real-time PCR (RT-qPCR), a sensitive technique is being extensively employed in quantification of gene expression. However this requires normalization with suitable reference gene (RG) which is crucial in minimizing inter sample variations. Information regarding suitable RG is scarce in general and more so in insects, including the cotton bollworm, Helicoverpa armigera, an economically important pest. In management of this pest RNA interference (RNAi), is perceived as a potential tool, which is achieved by double-stranded RNA (dsRNA) delivery. These studies demand accurate quantification of gene silencing. In this study we assessed the suitability of five RGs viz. ß-actin (ACTB), 18S rRNA (18S), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), ß-tubulin (TUB) and elongation fator-1-alfa (EF1-α) for gene expression studies in dsRNA treatment and across different developmental stages of H. armigera and ranked using geNorm, NormFinder and BestKeeper software programs. Data analysis revealed that best ranked RGs were varied in dsRNA treatment and in developmental stages. Under dsRNA treatment, 18S and GAPDH were more stable whereas, TUB and GAPDH were more stable across developmental stages. We also demonstrate that inappropriate selection of RG led to erroneous estimation of the target gene, chymotrypsin, expression. These results facilitate accurate quantification of gene expression in H. armigera.
Subject(s)
Chymotrypsin/genetics , Genes, Essential , Genes, Insect , Gossypium/parasitology , Lepidoptera/genetics , Real-Time Polymerase Chain Reaction/standards , Actins/genetics , Actins/metabolism , Animals , Chymotrypsin/antagonists & inhibitors , Chymotrypsin/metabolism , Gene Expression Regulation, Developmental , Genes, rRNA , Glyceraldehyde-3-Phosphate Dehydrogenase (NADP+)(Phosphorylating)/genetics , Glyceraldehyde-3-Phosphate Dehydrogenase (NADP+)(Phosphorylating)/metabolism , Larva/genetics , Larva/growth & development , Larva/metabolism , Lepidoptera/growth & development , Lepidoptera/metabolism , Peptide Elongation Factor 1/genetics , Peptide Elongation Factor 1/metabolism , RNA, Ribosomal, 18S/genetics , RNA, Ribosomal, 18S/metabolism , RNA, Small Interfering/genetics , RNA, Small Interfering/metabolism , Tubulin/genetics , Tubulin/metabolismABSTRACT
Tomato spotted wilt virus (TSWV) is an economically important virus that is transmitted in a persistent propagative manner by its thrips vector, Frankliniella occidentalis. Previously, we found that a soluble form of the envelope glycoprotein G(N) (G(N)-S) specifically bound thrips midguts and reduced the amount of detectable virus inside midgut tissues. The aim of this research was to (i) determine if G(N)-S alters TSWV transmission by thrips and, if so, (ii) determine the duration of this effect. In one study, insects were given an acquisition access period (AAP) with G(N)-S mixed with purified virus and individual insects were assayed for transmission. We found that G(N)-S reduced the percent of transmitting adults by eightfold. In a second study, thrips were given an AAP on G(N)-S protein and then placed on TSWV-infected plant material. Individual insects were assayed for transmission over three time intervals of 2 to 3, 4 to 5, and 6 to 7 days post-adult eclosion. We observed a significant reduction in virus transmission that persisted to the same degree throughout the time course. Real-time reverse transcription polymerase chain reaction analysis of virus titer in individual insects revealed that the proportion of thrips infected with virus was reduced threefold when insects were preexposed to the G(N)-S protein as compared to no exposure to protein, and nontransmitters were not infected with virus. These results demonstrate that thrips transmission of a tospovirus can be reduced by exogenous viral glycoprotein.
