Previous work by our group has detected the presence of a heterogeneous population of Ty1-copia-like reverse transcriptase retrotransposon sequences in the sweetpotato genome. Recently, we detected the presence of putatively active Ty1-copia-like reverse transcriptase sequences from a virus-infected `Beauregard' sweetpotato clone. In the current study, we report the differential detection of putatively stress-activated sequences in clones from seedling 91-189. The clones were infected with different combinations of virus isolates followed by extraction of leaf RNA samples at three sampling dates (weeks 2, 4, and 6) after inoculation. After repeated DNAse treatments to eliminate contaminating DNA, the RNA samples were subjected to first strand cDNA synthesis using random decamer primers followed by PCR analysis utilizing Ty1-copia reverse transcriptase-specific primers. Through this approach, we detected amplified fragments within the expected size range (280-300 bp) from clones infected with isolates of sweetpotato leaf curl (SPLC) and feathery mottle viruses (FMV) (week 2 and 6) and FMV (week 4). We were unable to detect PCR products from the noninfected clones or the other infected samples. The data suggests that specific viruses may be involved in the expression of these Ty1-copia-related reverse transcriptase sequences. It also appears that sampling at various dates is necessary to detect putative activity over time. This preliminary information is essential before proceeding to the construction and screening of cDNA libraries to isolate and fully characterize the putatively active sweetpotato Ty1-copia-like retrotransposon sequences. Through the partial or complete characterization of sweetpotato Ty1-copia elements, sequences that correspond to cis-regulatory element(s) can be identified and further studied for their roles in responding to specific stress factors.
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