Abstract
BackgroundPlant-mediated RNAi (PMRi) silencing of insect genes has enormous potential for crop protection, but whether it works robustly under field conditions, particularly with lepidopteran pests, remains controversial. Wild tobacco Nicotiana attenuata and cultivated tobacco (N. tabacum) (Solanaceae) is attacked by two closely related specialist herbivores Manduca sexta and M. quinquemaculata (Lepidoptera, Sphingidae). When M. sexta larvae attack transgenic N. attenuata plants expressing double-stranded RNA(dsRNA) targeting M. sexta’s midgut-expressed genes, the nicotine-ingestion induced cytochrome P450 monooxygenase (invert repeat (ir)CYP6B46-plants) and the lyciumoside-IV-ingestion induced β-glucosidase1 (irBG1-plants), these larval genes which are important for the larvae’s response to ingested host toxins, are strongly silenced.ResultsHere we show that the PMRi procedure also silences the homologous genes in native M. quinquemaculata larvae feeding on irCYP6B46 and irBG1-transgenic N. attenuata plants in nature. The PMRi lines shared 98 and 96% sequence similarity with M. quinquemaculata homologous coding sequences, and CYP6B46 and BG1 transcripts were reduced by ca. 90 and 80%, without reducing the transcripts of the larvae’s most similar, potential off-target genes.ConclusionsWe conclude that the PMRi procedure can robustly and specifically silence genes in native congeneric insects that share sufficient sequence similarity and with the careful selection of targets, might protect crops from attack by congeneric-groups of insect pests.
Highlights
Plant-mediated RNA interference (RNAi) (PMRi) silencing of insect genes has enormous potential for crop protection, but whether it works robustly under field conditions, with lepidopteran pests, remains controversial
Manduca sexta (Ms). sexta CYP6B46 and BG1 genes share high sequence similarity with M. quinquemaculata homologous genes Since Plant-mediated RNAi (PMRi) operates in a sequence specific manner to silence target gene transcripts, homologous gene silencing depends on sequence similarities between homologous genes in the regions that are used in the generation of the transgenic plants
We found that the M. sexta CYP6B46 fragment cloned to generate the irCYP6B46 plants shared 98% sequence similarity with the M. quinquemaculata CYP6B46 sequence (Fig. 2a) and that the M. sexta BG1 fragment cloned to generate the irBG1 plants shared 96% sequence similarity with the M. quinquemaculata BG1 sequence (Fig. 2b)
Summary
Plant-mediated RNAi (PMRi) silencing of insect genes has enormous potential for crop protection, but whether it works robustly under field conditions, with lepidopteran pests, remains controversial. When M. sexta larvae attack transgenic N. attenuata plants expressing double-stranded RNA(dsRNA) targeting M. sexta’s midgut-expressed genes, the nicotine-ingestion induced cytochrome P450 monooxygenase (invert repeat (ir)CYP6B46-plants) and the lyciumoside-IV-ingestion induced β-glucosidase (irBG1-plants), these larval genes which are important for the larvae’s response to ingested host toxins, are strongly silenced. Poreddy et al BMC Plant Biology (2017) 17:199 cotton bollworm defense genes using plant-mediated RNAi (PMRi) has been described by engineering host plants to produce dsRNAs directed against bollworm larvae’s P450 monooxygenase (CYP6AE14) gene in laboratory experiments [15]. Transplastomic potato plants were shown to be lethal to CPB larvae and were protected from CPB attack in glasshouse experiments [22]
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