Introduction

A plant-produced animal vaccine being developed in maize as a feed-based oral vaccine against transmissible gastroenteritis virus has been shown to effectively induce protective immunity in piglets. Soybean significantly trails behind maize and rice as a production platform for therapeutic antibodies, immune modulators, blood components, and vaccines. However, soybean has untapped potential for the commercial production of biopharmaceuticals (via recombinant proteins).

The advantage of soybean as a production crop is that, although it has a lower annual grain yield compared with corn and rice, the protein content of the seed is very high. Seeds have evolved to facilitate the accumulation of storage proteins in a small volume and stable environment. The desiccated nature of the mature seed allows for effective long-term storage.

To manipulate soybean seed composition to improve seed quality, break the protein/seed yield barrier and encourage the use of soybean for the production of "new" commercially valuable proteins, it is important to understand the biological mechanisms that control storage protein deposition and accumulation in seeds. If high-level production of a biopharmaceutical is to be achieved into soybean, an open and protected seed storage compartment may be required to achieve the levels of recombinant protein required to render an efficacious vaccine for oral delivery.

At the same time, incorporating into the system the ability to genetically select which seed compartment would be used to sequester the recombinant protein at an early seed fill stage, and when this compartment is accessible, might be beneficial not only for stable protein accumulation, but for desirable processing traits. For biosafety, incorporating temporal regulatory control into such a system could also be advantageous. Biotechnologies are now available to introduce both types of genetic switches into soybean for seed improvement and versatility.

Research Project

This project is specifically aimed at developing the methodologies for adapting a safe, effective and versatile genetic switching (GS) technology for use in soybean. The GS technology may be used to alter levels of oils, proteins, vitamins, and other nutritional factors in seeds, as well as to expedite the production of commercially valuable proteins.

A GS, based upon an ecdysone receptor (EcR)-based inducible system, will be adapted for use in the soybean seed. The GS is activated by the commercially available, environmentally-safe, nonsteroidal agonist, methoxyfenocide (MOF). A reporter gene, green fluorescent protein, whose seed-specific expression is controlled by a soybean blycinin promoter, will be used to demonstrate that the GS functions efficiently in soybean seed.

Using this ecdysone agonist-inducible system, the researchers will confirm that the chemical inducer is taken up and transported throughout the plant, and is capable of activating reporter gene expression specifically in seed. The optimal ligand concentration required for gene induction, preferred mode of ligand application, optimal timing for seed-specific gene induction and protein accumulation, will be determined using the experimental transgenic plant lines developed.

Expected Outcomes

Knowledge gained will be used to optimize the technology of adaptation of soybean seed for the production of biopharmaceutical proteins, especially for improved animal health and disease immunity.

Developing soybean lines with the ability to activate specific gene expression in the seed and/or shunt the compartmentalization of a specific gene product from one storage location to another may give soybean a commercial advantage as a production platform.