We report success of host-induced gene silencing in downregulation of aflatoxin biosynthesis in Aspergillus flavus infecting maize transformed with a hairpin construct targeting transcription factor aflR. Infestation of crops by aflatoxin-producing fungi results in economic losses as well as negative human and animal health effects. Currently, the control strategies against aflatoxin accumulation are not effective to the small holder farming systems in Africa and this has led to widespread aflatoxin exposure especially in rural populations of sub-Saharan Africa that rely on maize as a staple food crop. A recent strategy called host-induced gene silencing holds great potential for developing aflatoxin-resistant plant germplasm for the African context where farmers are unable to make further investments other than access to the germplasm. We transformed maize with a hairpin construct targeting the aflatoxin biosynthesis transcription factor aflR. The developed transgenic maize were challenged with an aflatoxigenic Aspergillus flavus strain from Eastern Kenya, a region endemic to aflatoxin outbreaks. Our results indicated that aflR was downregulated in A. flavus colonizing transgenic maize. Further, maize kernels from transgenic plants accumulated significantly lower levels of aflatoxins (14-fold) than those from wild type plants. Interestingly, we observed that our silencing cassette caused stunting and reduced kernel placement in the transgenic maize. This could have been due to "off-target" silencing of unintended genes in transformed plants by aflR siRNAs. Overall, this work indicates that host-induced gene silencing has potential in developing aflatoxin-resistant germplasm.

BackgroundOnce a transgenic plant is developed, the selectable marker gene (SMG) becomes unnecessary in the plant. In fact, the continued presence of the SMG in the transgenic plant may cause unexpected pleiotropic effects as well as environmental or biosafety issues. Several methods for removal of SMGs that have been reported remain inaccessible due to protection by patents, while development of new ones is expensive and cost prohibitive. Here, we describe the development of a new vector for producing marker-free plants by simply adapting an ordinary binary vector to the double right border (DRB) vector design using conventional cloning procedures.FindingsWe developed the DRB vector pMarkfree5.0 by placing the bar gene (representing genes of interest) between two copies of T-DNA right border sequences. The β-glucuronidase (gus) and nptII genes (representing the selectable marker gene) were cloned next followed by one copy of the left border sequence. When tested in a model species (tobacco), this vector system enabled the generation of 55.6% kanamycin-resistant plants by Agrobacterium-mediated transformation. The frequency of cotransformation of the nptII and bar transgenes using the vector was 66.7%. Using the leaf bleach and Basta assays, we confirmed that the nptII and bar transgenes were coexpressed and segregated independently in the transgenic plants. This enable separation of the transgenes in plants cotransformed using pMarkfree5.0.ConclusionsThe results suggest that the DRB system developed here is a practical and effective approach for separation of gene(s) of interest from a SMG and production of SMG-free plants. Therefore this system could be instrumental in production of “clean” plants containing genes of agronomic importance.

No abstract

No abstract

No abstract

This study aimed at to improve drought resilience of sorghum germplasm through development of screening techniques for sustainable food security. Also this study aimed at creating knowledge on the response of farmers’ preferred sorghum varieties to water deficit tolerance under Gezira irrigated conditions. Results from this study proved that Tabat showed susceptibility to drought at the four water treatments while Yarwahsa showed resistance to drought at all water treatments especially at 65 days after sowing. Also YR-2 had the best head weight and number of green leaves across all treatments. Future evaluation of the studied cultivars showld be carried on to confirm their tolerance and stability under water deficit conditions would be useful.

Background and Objective: Several factors affect the optimization of tissue culture protocols of cereals including hormones and media composition. This the first study in East and Central Africa to assess the effect of the hormone 2,4-D on callus initiation and regeneration of sweet sorghum via mature embryos. Materials and Methods: Callus induction and regeneration of 5 sweet sorghum varieties IESV92008DL, IESV92001DL, IESV92021DL, ICSV700 and ICSV93048 were evaluated using mature embryos as a source of explants and MS medium supplemented with five levels of the hormone 2,4-D (0, 1, 2, 4 and 6 mg LG 1 ). Results: The highest callus induction frequency was observed in 6 mg LG 1 of 2,4-D level for all the genotypes while the lowest callus induction frequency was observed in 0 and 1mg LG 1 of 2,4-D level. The highest embryogenic callus induction frequency was observed in 4 and 6 mg LG 1 of 2,4-D for all the genotypes while the lowest embryogenic callus induction frequency was observed in 0 and 1 mg LG 1 of 2,4-D. Regeneration efficiency was observed higher for the 2 genotypes ICSV93046 and ICSV700. Conclusion: This study revealed that the auxin 2,4-D level 4 and 4 mg LG 1 are very important for callus initiation and regeneration of sweet sorghum and helpful for researcher to set up other protocols for improvement of sweet sorghum crop through tissue culture and transformation techniques.