Historically, most vaccines have been based on killed or live‐attenuated infectious agents. Although very successful at immunizing populations against disease, both approaches raise safety concerns and often have limited production capacity. This has resulted in increased emphasis on the development of subunit vaccines. Several recombinant systems have been considered for subunit vaccine manufacture, including plants, which offer advantages both in cost and in scale of production. We have developed a plant expression system utilizing a ‘launch vector’, which combines the advantageous features of standard agrobacterial binary plasmids and plant viral vectors, to achieve high‐level target antigen expression in plants. As an additional feature, to aid in target expression, stability and purification, we have engineered a thermostable carrier molecule to which antigens are fused. We have applied this launch vector/carrier system to engineer and express target antigens from various pathogens, including, influenza A/Vietnam/04 (H5N1) virus.

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Peach latent mosaic viroid (PLMVd) is widely distributed (approximately 55%) in peach germplasm from Europe, Asia, North America, and South America. PLMVd, or a closely related viroid, was occasionally detected in cherry, plum, and apricot germplasm from countries in Europe or Asia. The cherry isolate of PLMVd is 337 nucleotides in length and is 91 to 92% homologous to PLMVd isolates from peach. Molecular hybridization experiments demonstrated that PLMVd is not related to the agent of peach mosaic disease. PLMVd was readily transmitted (50 to 70%) by contaminated blades to green shoots and lignified stems of peach GF-305 plants. These results indicate that the viroid may be transmitted in orchards with contaminated pruning equipment.

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