Abstract
BackgroundStriga hermonthica is a hemiparasitic weed that infects cereals in Sub Sahara Africa (SSA) resulting in up to 100% grain yield loss. This significant loss in grain yields is a major contributor to food insecurity and poverty in the region. Current strategies to control the parasite are costly, unavailable and remain unpracticed by small-scale farmers, underscoring the need for more economical and sustainable control strategies. Development of resistant germplasm is the most sustainable strategy in the control of S. hermonthica, but is constrained by paucity of resistance genes for introduction into crop germplasm. RNA interference (RNAi) has potential for developing host-derived resistance against S. hermonthica by transformation of host crops with RNAi sequences targeted at critical Striga genes. The application of RNAi in management of S. hermonthica is however constrained by lack of efficient high throughput screening protocols for the candidate genes for silencing, as well as sub optimal delivery of siRNAs into the parasite. In comparison to stable transformation, viral induced gene silencing (VIGS) is a rapid and powerful tool for plant functional genomics and provides an easy and effective strategy in screening for putative candidate genes to target through RNAi. In addition, VIGS allows for a secondary amplification of the RNAi signal increasing the siRNA threshold and facilitates siRNA transport through viral movement proteins. We tested the efficiency of the Tobacco rattle virus (TRV1 and TRV2) VIGS vectors in silencing S. hermonthica phytoene desaturase (PDS) gene through agrodrench and agro-infiltration.ResultsWe report the validation of VIGS in S. hermonthica using a silencing cassette generated from TRV with a PDS gene insert. Agro-infiltrated and agro-drenched S. hermonthica leaves showed photo-bleaching phenotypes typical for PDS silencing within 7 and 14 days post infection respectively. In both cases S. hermonthica plants recovered from photo-bleaching effects within 28 days post inoculation. The transformation efficiency of the VIGS protocol in S. hermonthica was (60 ± 2.9)%.ConclusionThese results demonstrate that the TRV-VIGS system work in S. hermonthica and can be used for candidate gene validation for their role in the parasite development and parasitism, with the ultimate goal of developing resistant transgenic maize.
Highlights
viral induced gene silencing (VIGS) induced RNA interference (RNAi) on S. hermonthica phytoene desaturase (PDS) causes photo-bleaching Viral induced technique through agro-drench methods was effective in S. hermonthica plants
This was evidenced by down regulation of the PDS gene resulting into photo-bleached phenotypes on the leaves of S. hermonthica plants
This was evidenced by down-regulation of the PDS gene in S. hermonthica plants resulting in photo bleaching phenotypes at 7 and 14 days post inoculation in agro-infiltrated and agro-drenched plants respectively
Summary
Striga hermonthica is a hemiparasitic weed that infects cereals in Sub Sahara Africa (SSA) resulting in up to 100% grain yield loss. This significant loss in grain yields is a major contributor to food insecurity and poverty in the region. Development of resistant germplasm is the most sustainable strategy in the control of S. hermonthica, but is constrained by paucity of resistance genes for introduction into crop germplasm. The most devastating biotic constraint to maize production in SSA is Striga hermonthica (Del.) Bentha, a root hemi-parasitic weed of maize which causes up to 100% grain loss annually [3,6,7]. Some S. hermonthica control strategies have been proposed and practiced, Striga seed bank in soils has continued to build up and the parasite has continued to spread to previously non-infected arable land [10,11]
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