Cassava Mosaic Geminiviruses (CMGs)

An important research component in the Fondong lab is geminivirus—plant interactions. Our geminivirus studies focus on cassava mosaic geminiviruses (CMGs), which cause the cassava mosaic disease (CMD) in cassava (Manihot esculenta) in Africa and southeastern Asia. CMD is one of the most devastating plant diseases of virus origin. CMGs belong to the family Geminiviridae, genus Begomovirus (other genera include Mastrevirus, Curtovirus and Topocuvirus) and are transmitted by whitefly-vectors and through infected stem cuttings. CMG genomes have two circular single-stranded DNA (ssDNA) molecules, DNA-A and DNA-B, each about 2.8 kb and packaged as minichromosomes. These viruses routinely co-infect the same plants causing a synergistic interaction as exhibited by East African cassava mosaic Cameroon virus (EACMCV) and African cassava mosaic virus (ACMV). We have also shown that ACMV—infected plants recover from infection within three weeks of infection. This recovery is, at partially, explained by posttranscriptional gene silencing (PTGS). We design our transgenes for virus resistant plants based on the PTGS mechanism.

Plant-Based Vaccine Production

We conduct research on plant-based vaccine production, which has overtaken traditional systems involving fungi, bacteria, yeast, insects, mammalian cells, and transgenic mammals as a method of choice for large-scale production of vaccines and pharmaceutical recombinant proteins. This is because plants have several advantages over traditional systems, these advantages include (1) low cost of production, (2) production of multimeric proteins, such as antibodies, (3) no disease hazard—plants are not hosts of human pathogens, and (4) glycosylation—making vaccines stable. Our efforts are directed at optimizing plant-based production systems by targeting these proteins to specific compartments of the cell and reducing the effect of gene silencing. The plant species we currently use is a wild tobacco, Nicotiana benthamiana and vaccines being used in the researched include Human immunodeficiency virus type 1 (HIV-1) and Respiratory syncytial virus (RSV) candidate vaccines.

 

Vincent Fondong

Vincent Fondong, PhD
Associate Professor of Biotechnology

Delaware State University
Department of Biological Sciences
1200 North DuPont Highway
Dover, DE 19901
Ph. 302-857-7377
Fx. 302-857-6512

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Figure 1

Figure 1 Figure 2

Symptoms of cassava mosaic disease (CMD) a) CMD on a cassava plant doubly infected by African cassava mosaic virus and East African cassava mosaic Cameroon virus in the south-western rainforest region of Cameroon. In such severe cases there is defoliation of the stem shoot. b) In the area of the cassava geminivirus epidemic, severely affected plants resulting from dual infection can be found growing next to mildly affected plants that result from infection by one virus.

Figure 2

Figure 2

The cassava geminivirus DNA-A encodes six genes, two in the virus sense: AV1, which codes for the coat protein (CP) and the AV2 protein; four of the genes are in the complementary sense including AC1, which codes for replication—associated protein (Rep); AC2 and AC3, which code for the transcription activation protein (TrAP) and the replication enhancer protein (REn) respectively, and AC4, which is involved in pathogenesis of the virus. The DNA-B encodes two genes, BV1 and BC1, which code for the movement protein (MP) and the nuclear shuttle protein (NSP), respectively.