The familyRhizobiaceaecontains plant-associated bacteria with critical roles in ecology and agriculture. Within this family, manyRhizobiumandSinorhizobiumstrains are nitrogen-fixing plant mutualists, while many strains designated asAgrobacteriumare plant pathogens. These contrasting lifestyles are primarily dependent on the transmissible plasmids each strain harbors. Members of theRhizobiaceaealso have diverse genome architectures that include single chromosomes, multiple chromosomes, and plasmids of various sizes.Agrobacteriumstrains have been divided into three biovars, based on physiological and biochemical properties. The genome of a biovar I strain,A. tumefaciensC58, has been previously sequenced. In this study, the genomes of the biovar II strainA. radiobacterK84, a commercially available biological control strain that inhibits certain pathogenic agrobacteria, and the biovar III strainA. vitisS4, a narrow-host-range strain that infects grapes and invokes a hypersensitive response on nonhost plants, were fully sequenced and annotated. Comparison with other sequenced members of theAlphaproteobacteriaprovides new data on the evolution of multipartite bacterial genomes. Primary chromosomes show extensive conservation of both gene content and order. In contrast, secondary chromosomes share smaller percentages of genes, and conserved gene order is restricted to short blocks. We propose that secondary chromosomes originated from an ancestral plasmid to which genes have been transferred from a progenitor primary chromosome. Similar patterns are observed in selectBeta- andGammaproteobacteriaspecies. Together, these results define the evolution of chromosome architecture and gene content among theRhizobiaceaeand support a generalized mechanism for second-chromosome formation among bacteria.

Virus-like particles (VLPs) are self-assembled structures derived from viral antigens that mimic the native architecture of viruses but lack the viral genome. VLPs have emerged as a premier vaccine platform due to their advantages in safety, immunogenicity, and manufacturing. The particulate nature and high-density presentation of viral structure proteins on their surface also render VLPs as attractive carriers for displaying foreign epitopes. Consequently, several VLP-based vaccines have been licensed for human use and achieved significant clinical and economical success. The major challenge, however, is to develop novel production platforms that can deliver VLP-based vaccines while significantly reducing production times and costs. Therefore, this review focuses on the essential role of plants as a novel, speedy and economical production platform for VLP-based vaccines. The advantages of plant expression systems are discussed in light of their distinctive posttranslational modifications, cost-effectiveness, production speed, and scalability. Recent achievements in the expression and assembly of VLPs and their chimeric derivatives in plant systems as well as their immunogenicity in animal models are presented. Results of human clinical trials demonstrating the safety and efficacy of plant-derived VLPs are also detailed. Moreover, the promising implications of the recent creation of “humanized” glycosylation plant lines as well as the very recent approval of the first plant-made biologics by the U. S. Food and Drug Administration (FDA) for plant production and commercialization of VLP-based vaccines are discussed. It is speculated that the combined potential of plant expression systems and VLP technology will lead to the emergence of successful vaccines and novel applications of VLPs in the near future.