Plants viruses are increasingly being examined as alternative recombinant protein expression systems. Future development of plant virus expression vectors needs to focus on the most important economic hosts, namely cereals and legumes, to develop tools to aid breeding of such hosts and systems for edible vaccine production.

Sunn hemp mosaic virus (SHMV) is a tobamovirus, which infects leguminous plants. This work reports on new SHMV-based viral vectors for high yield of target proteins in legumes. In the SHEC vector series, the coat protein gene of SHMV was substituted by a reporter gene. In the SHAC vector series, the coat protein was substituted by a reporter gene and the coat protein gene from another tobamovirus, tobacco mild green mosaic virus (TMGMV). Co-agroinoculation of SHEC/GFP with an RNA silencing suppressor resulted in high levels of local GFP expression by 3 days post inoculation. Co-agroinoculation with SHAC/GFP led to systemic fluorescence in 12-19 dpi.

Foxtail mosaic virus (FoMV) is a species of the group Potexvirus , which infects cereal plants. A new viral vector series named FECT was constructed by eliminating the triple gene block and coat protein genes, reducing the viral genome by 29%. Interestingly, agroinoculation of the vector alone results in only slight transient expression, whereas co-inoculation with silencing suppressor genes allows for GFP expression of 40% total soluble protein. Full-sized HC and LC components of an anti-langerin IgG, each carried by a separate FECT vector, expressed and folded into immunologically functional antibody upon co-inoculation. This may prove a useful and environmentally safe vector for both transient expression and perhaps transgenic plants.

Mountain cedar (Juniperus ashei) pollen causes severe allergies in Texas and the central USA. Jun a 1 is the dominant allergen protein of mountain cedar pollen and would be a good allergen vaccine candidate. Recombinant Jun a 1 was expressed in Nicotiana benthamiana using an agroinoculation-compatible tobacco mosaic virus vector and isolated in good quantity from the apoplast by vacuum infiltration (100 μg/g leaf material). The recombinant protein samples were characterized. Pectate lyase activity was detected from plant extracts, suggesting the cause of severe necrotic reaction in plants.