Transcriptome analysis of component interactions in a tospovirus pathosystem
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In this study, we characterized molecular interactions between Tomato spotted wilt virus (TSWV), its host plant, and its vector and non-vector thrips species. Using a transcriptomic approach, we presented descriptive studies of transcripts associated with TSWV transmission and assigned putative functions to transctipts based on sequence similarity. The first objective elucidated TSWV-induced changes in various life stages of Frankliniella fusca [Hinds] at transcript levels. Differential expression analysis revealed upregulation of contigs associated with virus entry, replication, and immune response in viruliferous thrips. Upregulated contigs in viruliferous adults had a annotation associated with egg production, while in larvae; downregulated contigs were associated with development. In the second objective, F. fusca and a non-vector, Frankliniella tritici [Fitch] transcriptomes were compared to examine if molecular factors determine thrips’ ability to transmit TSWV. Some differences in virus reception, virus infection, and immunity were documented at qualitative levels. Nonetheless, a majority of genes present in F. tritici were also present in F. fusca, suggesting species-specific membrane barriers could further facilitate determination of thrips’ ability to transmit TSWV. In the third objective, the vector status of Echinothrips americanus [Morgan] was evaluated for TSWV, and transcriptomes of E. americanus and F. fusca were compared. TSWV replication was restricted to midgut tissues of E. americanus. Also, E. americanus did not transmit TSWV to plants. Further, homologs of proteins associated with virus reception, infection, and immunity were present in E. americanus and F. fusca, suggesting E. americanus is a non-vector of TSWV and the incompetence of E. americanus to transmit TSWV could be associated with lack of salivary gland infection caused by physical barriers restricting TSWV movement. The fourth objective investigated TSWV-induced changes in susceptible (SunOleic 97R) and resistant (Tifguard) peanut genotypes at transcript levels to elucidate molecular mechanisms underlying TSWV resistance in resistant genotypes. TSWV-infection upregulated contigs related to biotic and abiotic stimulus in SunOleic and Tifguard. Upregulated contigs were mainly associated with disease resistance and RNA silencing. The number and type of constitutive and induced defense related proteins were more in Tifguard than in SunOleic, indicating defense system could be more robust in Tifguard than in SunOleic.