Tichafa R. I. Munyikwa

Bio: Tichafa R. I. Munyikwa is an academic researcher from Monsanto. The author has contributed to research in topics: Transgene & Gene. The author has an hindex of 5, co-authored 9 publications receiving 1644 citations.

Control of coleopteran insect pests through RNA interference

Abstract: Commercial biotechnology solutions for controlling lepidopteran and coleopteran insect pests on crops depend on the expression of Bacillus thuringiensis insecticidal proteins1,2, most of which permeabilize the membranes of gut epithelial cells of susceptible insects3 However, insect control strategies involving a different mode of action would be valuable for managing the emergence of insect resistance Toward this end, we demonstrate that ingestion of double-stranded (ds)RNAs supplied in an artificial diet triggers RNA interference in several coleopteran species, most notably the western corn rootworm (WCR) Diabrotica virgifera virgifera LeConte This may result in larval stunting and mortality Transgenic corn plants engineered to express WCR dsRNAs show a significant reduction in WCR feeding damage in a growth chamber assay, suggesting that the RNAi pathway can be exploited to control insect pests via in planta expression of a dsRNA

Compositions and methods for control of insect infestations in plants

Abstract: The present invention is directed to controlling pest infestation by inhibiting one or more biological functions in an invertebrate pest. The invention discloses methods and compositions for use in controlling pest infestation by feeding one or more different recombinant double stranded RNA molecules to the pest in order to achieve a reduction in pest infestation through suppression of gene expression. The invention is also directed to methods for making transgenic plants that express the double stranded RNA molecules, and to particular combinations of transgenic pesticidal agents for use in protecting plants from pest infestation.

MicroTom--a high-throughput model transformation system for functional genomics.

Abstract: We have developed a high-throughput Agrobacterium-mediated transformation model system using both nptII and the 5-enolpyruvylshikimate-3-phosphate synthase gene from Agrobacterium tumefaciens strain CP4 (cp4) based selections in MicroTom, a miniature rapid-cycling cherry tomato variety. With the NPTII selection system, transformation frequency calculated as independent transgenic events per inoculated explant ranged from 24 to 80% with an average of 56%, in industrial production scale transformation experiments. For CP4, with glyphosate selection, the average transformation frequency was 57%. Stable transformation frequency was positively correlated with transient expression (R=0.85), and variable with the genes of interest. DNA integration and germline transformation were confirmed by biological assay, Southern Blot analysis, and R1 phenotype segregation. Transgene expression was observed in leaf, root, stem, flower, and fruit tissues of the transgenic plants. Ninety-five percent of transgenic events coexpressed two introduced genes based on β-glucuronidase (GUS) and neonmycin phosphotransferase II (NPTII) expression. Seventy-five percent of transgenic events contained one to two copies of the introduced uidA (GUS) gene based on Southern analysis. Transgenic plants from the cotyledon explants to the transgenic plants transferred to soil were produced within about 2–3 months depending on the genes of interest. The utility of this MicroTom model transformation system for functional genomic studies, such as identification of genes related to important agricultural traits and gene function, is discussed.

Selecting and stabilizing dsrna constructs

Abstract: The invention provides methods for selecting nucleotide sequences that yield dsRNA- mediated gene suppression in a target organism and enable their uptake by the target organism. The invention further provides expression constructs that confer stabilized expression of such sequences in a transgenic host cell, and methods for their use. Also provided are organisms, cells and tissues prepared by a method of the invention.

Modified gene silencing

Abstract: This invention relates to methods of controlling gene expression or gene suppression in eukaryotic cells. One aspect of this invention includes modifying the degree of silencing of a target gene by use of a modified suppression element. Another aspect includes providing a eukaryotic cell having a desired phenotype resulting from transcription in the eukaryotic cell of a modified suppression element. Also provided are transgenic eukaryotic cells, transgenic plant cells, plants, and seeds containing modified suppression elements, and useful derivatives of such transgenic plant cells, plants, or seeds, such as food or feed products.

Insect resistance to Bt crops: lessons from the first billion acres

Abstract: Evolution of resistance in pests can reduce the effectiveness of insecticidal proteins from Bacillus thuringiensis (Bt) produced by transgenic crops We analyzed results of 77 studies from five continents reporting field monitoring data for resistance to Bt crops, empirical evaluation of factors affecting resistance or both Although most pest populations remained susceptible, reduced efficacy of Bt crops caused by field-evolved resistance has been reported now for some populations of 5 of 13 major pest species examined, compared with resistant populations of only one pest species in 2005 Field outcomes support theoretical predictions that factors delaying resistance include recessive inheritance of resistance, low initial frequency of resistance alleles, abundant refuges of non-Bt host plants and two-toxin Bt crops deployed separately from one-toxin Bt crops The results imply that proactive evaluation of the inheritance and initial frequency of resistance are useful for predicting the risk of resistance and improving strategies to sustain the effectiveness of Bt crops

Insect resistance to Bt crops: evidence versus theory

Abstract: Evolution of insect resistance threatens the continued success of transgenic crops producing Bacillus thuringiensis (Bt) toxins that kill pests. The approach used most widely to delay insect resistance to Bt crops is the refuge strategy, which requires refuges of host plants without Bt toxins near Bt crops to promote survival of susceptible pests. However, large-scale tests of the refuge strategy have been problematic. Analysis of more than a decade of global monitoring data reveals that the frequency of resistance alleles has increased substantially in some field populations of Helicoverpa zea, but not in five other major pests in Australia, China, Spain and the United States. The resistance of H. zea to Bt toxin Cry1Ac in transgenic cotton has not caused widespread crop failures, in part because other tactics augment control of this pest. The field outcomes documented with monitoring data are consistent with the theory underlying the refuge strategy, suggesting that refuges have helped to delay resistance.