M J Roossinck

..These novel findings are leading to re-evaluation of the relationships between subviral RNAs, helper viruses, and hosts...

..How these beneficial interactions evolve is still a mystery in many cases but, as discussed in this Review, the mechanisms of these interactions are beginning to be understood in more detail...

..These obstacles are being overcome in clever ways. Understanding what exists in our natural environment will help us to tackle big issues in agriculture, such as disease emergence and the use of beneficial viruses and other microbes...

..In viruses, symbiogenesis results in genomic reassortment or recombination events among disparate species. These are most noticeable by phylogenetic comparisons of extant viruses from different taxonomic groups...

..Here we describe the method in detail, including the results and analysis for eight pools of samples. This technology will be extremely useful in understanding the full scope of plant virus biodiversity...

..Recent advances include new insights into the origins of plant viruses, analyses of quasispecies and mutation frequencies, population studies on field isolates and practical studies on the importance of virus evolution to agriculture...

..Persistent, chronic and acute lifestyles of plant viruses are contrasted from both a functional and evolutionary perspective, and the potential role of these lifestyles in host evolution is discussed...

..This indicates that functions other than replication are encoded in the 3' NTR. Reassortment may have led to the genetic diversity found among CMV strains and contributed to its enormous evolutionary success...

..In addition, strains within each subgroup radiate from a single point of origin, indicating that they have evolved from a single common ancestor for each subgroup...

..However, the potential for understanding mutualism and how a virus might become a mutualist may be elucidated by understanding these dynamics...

..Many more analyses are required before generalized patterns can be determined...

..Support of satellite RNA in whole plants and in protoplasts of zucchini squash is analyzed...

..Recombinant cDNA clones of D4 sat-RNA and WL47 sat-RNA were used to map the sat-RNA sequences responsible for the helper virus selection of a specific sat-RNA for amplification...

..The virus-infected fungus confers heat tolerance not only to its native monocot host but also to a eudicot host, which suggests that the underlying mechanism involves pathways conserved between these two groups of plants...

..protuberata in culture. The results assist in understanding the molecular basis of thermotolerance of the three-way symbiosis. Further studies will confirm or refute the involvement of these pathways in stress tolerance...

..RNA extracted from purified CCMV particles showed all four RNA components by agarose gel electrophoresis. Both purified virus particles and RNA were biologically active and initiated successful infection upon inoculation to cowpea...

..In greenhouse studies, satellites have been known to "spontaneously" appear in virus cultures. The possible origin of satellites will be briefly considered...

..We show here that the genetic variation in a defined population of an RNA virus is significantly, stochastically, and reproducibly reduced during the systemic infection process, providing clear evidence of a genetic bottleneck...

..Quasispecies cloud size for these viruses is related to host-virus interactions, and understanding these interactions may facilitate the prediction and prevention of emerging viral diseases...

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..Additional experiments demonstrated that genetic variation in the artificial population of CMV is not reduced during the acquisition of the virus but is significantly reduced during the inoculation period...

..The spatial and temporal expression patterns of these genes as detected by RNA in situ hybridization point to the involvement of a complex developmental program that accompanies disease development resulting from CMV/D satRNA infection...

..Results from Northern blot analysis demonstrated the partial contribution of ethylene in the induced defense responses in CMV/D satRNA-infected plants...

..Analysis of the accumulation of minus- and plus-strand satRNAs in the infected plants indicates a correlation between high amounts of minus-strand satRNA and tomato cell death...

..These results have implications for the differences in virus population variation that is seen in different host plants...

..Hence, expression of these animal antiapoptotic genes improved plant survival under abiotic or biotic stress...

..Deletion mutation rates were different for the two hosts tested, although the mutation distribution was not influenced by the hosts. Moreover, hot spots with high mutation rates were identified on the satRNA genome...

..These results indicate that virus infection improves plant tolerance to abiotic stress, which correlates with increased osmoprotectant and antioxidant levels in infected plants...