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Camargo RA, Barbosa GO, Possignolo IP, Peres LEP, Lam E, Lima JE, Figueira AVO, Marques-Souza H.2016. RNA interference as a gene silencing tool to control Tuta absoluta in tomato (Solanum lycopersicum)PeerJ Preprints4:e2406v1https://doi.org/10.7287/peerj.preprints.2406v1
RNA interference (RNAi), a gene-silencing mechanism that involves providing double-stranded RNA molecules that match a specific target gene sequence, is now widely used in functional genetic studies. The potential application of RNAi-mediated control of agricultural insect pests has rapidly become evident. The production of transgenic plants expressing dsRNA molecules that target essential insect genes could provide a means of specific gene silencing in larvae that feed on these plants, resulting in larval phenotypes that range from loss of appetite to death. In this report, we show that the tomato leafminer (Tuta absoluta), a major threat to commercial tomato production, can be targeted by RNAi. We selected two target genes [Vacuolar ATPase-A and Arginine kinase] based on the RNAi response reported for these genes in other pest species. In view of the lack of an artificial diet for T. absoluta, we used two approaches to deliver dsRNA into tomato leaflets. The first approach was based on the uptake of dsRNA by leaflets and the second was based on “in planta-induced transient gene silencing” (PITGS), a well-established method for silencing plant genes, used here for the first time to deliver in planta-transcribed dsRNA to target insect genes. Tuta absoluta larvae that fed on leaves containing dsRNA of the target genes showed an ~60% reduction in target gene transcript accumulation, an increase in larval mortality and less leaf damage. We then generated transgenic ‘Micro-Tom’ tomato plants that expressed hairpin sequences for both genes and observed a reduction in foliar damage by T. absoluta in these plants. Our results demonstrate the feasibility of RNAi as an alternative method for controlling this critical tomato pest.
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Multiple alignment of translated cloned sequences from Tuta absoluta and homologues from other insect species
For Vacuolar ATPase subunit-A: Aedes aegypti (XP_001659520.1); Drosophila melanogaster (NP_652004.2); Tribolium castaneum (XP_976188.1); Manduca sexta (P31400.1); Bombyx mori (NP_001091829.1); Tuta absoluta (KM591219). Arginine Kinase: Spodoptera litura (ADW94627.1); Helicoverpa armigera (ADD22718.1); Bombyx mori (NP_001037402.1); Tribolium castaneum (EFA11419.1); Homalodisca vitripennis (AAT01074.1); Drosophila melanogaster (AAA68172.1); Tuta absoluta (KM591220).
Agroinfiltration experiments with Agrobacterium expressing eGFP or eGFP plus GFPi
(A) Expression of eGFP in tomato leaf infiltrated with Agrobacterium suspension containing plasmid with eGFP, visualized under a confocal fluorescent microscope. (B) Infiltration of tomato leaf with two Agrobacterium clones, expressing eGFP together with a construct expressing GFPi, indicating reduction in GFP expression visualized under confocal fluorescent microscope. (C) tomato leaf tissues at a distance away from the area infiltrated with Agrobacterium suspension containing plasmid with eGFP (bar = 100 μm).
Tuta absoluta individuals after feeding for 11 days in tomato leaflets, after absorbing 500 ng dsRNA of the GFP control (a) and the target genes V-ATPase (b) or AK (c). Total amount of individuals at pupal stage, resultant from the larvae feeding on GFP control (d) and the target genes V-ATPase (e) or AK (f)
Amplification detection of expressed sequences (cDNA; siRNA and microRNA) from various transgenic events
(A) Detection of amplification products from cDNA (RT-PCR) extracted from various transgenic ‘Micro-tom’ events and non-transformed control (WT) using primers specific for insect V-ATPase (top panel; 139 bp) or AK (bottom panel;190 bp), and tomato ubiquitin (108 bp). (B). Detection of amplification products derived from stem loop pulsed RT-PCR for potential siRNA derived from target genes (V-ATPase or AK, both 60 bp), plus the microRNA156 (MIR156; 60 bp) control ran at 3% agarose gel electrophoresis. Numbers represent events (1st number) or plants within events (2nd number).
List of primers to detect siRNA in transgenic plants
Gene-specific and the universal primer sequences used to detect the predicted small interfering RNAs (siRNA) derived from the target genes V-ATPase (siRNA AATACATGCGCGCTCTAGATGAC) and AK (siRNA AAGTATCGTCCACACTGTCTGGC) and the control microRNA156 (UGACAGAAGAGAGUGAGCAC) in transgenic plants.