Polydnavirus genomes reflect their dual roles as mutualists and pathogens.

Symbionts often exhibit significant reductions in genome complexity while pathogens often exhibit increased complexity through acquisition and diversification of virulence determinants. A few organisms have evolved complex life cycles in which they interact as symbionts with one host and pathogens with another. How the predicted and opposing influences of symbiosis and pathogenesis affect genome evolution in such instances, however, is unclear. The Polydnaviridae is a family of double-stranded (ds) DNA viruses associated with parasitoid wasps that parasitize other insects. Polydnaviruses (PDVs) only replicate in wasps but infect and cause severe disease in parasitized hosts. This disease is essential for survival of the parasitoid's offspring. Thus, a true mutualism exists between PDVs and wasps as viral transmission depends on parasitoid survival and parasitoid survival depends on viral infection of the wasp's host. To investigate how life cycle and ancestry affect PDVs, we compared the genomes of Campoletis sonorensis ichnovirus (CsIV) and Microplitis demolitor bracovirus (MdBV). CsIV and MdBV have no direct common ancestor, yet their encapsidated genomes share several features including segmentation, diversification of virulence genes into families, and the absence of genes required for replication. In contrast, CsIV and MdBV share few genes expressed in parasitized hosts. We conclude that the similar organizational features of PDV genomes reflect their shared life cycle but that PDVs associated with ichneumonid and braconid wasps have likely evolved different strategies to cause disease in the wasp's host and promote parasitoid survival.

A physical, enzymatic, and genetic characterization of perturbations in the seeds of the brownseed tomato mutants.

The brownseed mutants (bs(1), bs(2), and bs(4)) of tomato all possess dark testae and deleteriously affect seed germination speed and/or final percentage. Poor germination performance of the bs(1) but not the bs(4) mutant, was due to greater impediment to radicle egress. Testa toughening (bs(1)) was prevented by drying in N(2). However, poor germination speed was hardly affected by drying. GA(4+7) did not ameliorate germination percentage or speed (bs(1), bs(2)), whereas bs(4) seeds commenced radicle protrusion sooner and had a greater germination percentage. bs(1) mutant seeds have two times more catalase activity while those of bs(4) contained six times more peroxidase and almost two times more catalase activity than WTs. bs(4) release only half of the reactive oxygen species into the media than WT during imbibition. EPR detected the presence of free radicals in bs(1) and its WT. bs mutants were epistatic to 12 anthocyaninless mutations, at least some of which produce seeds of lighter than usual testa colour. Macro-arrays of subtractive, suppressive PCR products identified differentially regulated transcripts between seeds of bs(4) and WT. EST identity suggests bs(4) does not exit the developmental programme upon attaining maturity.