Transcriptomic and Functional Analyses Indicate Novel Anti-viral Mode of Actions on Tobacco Mosaic Virus of a Microbial Natural Product ε‑Poly‑l‑lysine

Novel anti-viral natural product
ε-poly-l-lysine
(ε-PL) produced by Streptomyces is a homopolymer of l-lysine, of which the underlying molecular
mode of action remains to be further elucidated. In this study, ε-PL
induced significant fragmentation of tobacco mosaic virus (TMV) virions
and delayed the systemic infection of TMV-GFP as well as wild-type
TMV in plants. ε-PL treatment also markedly inhibited RNA accumulation
of TMV in tobacco BY-2 protoplasts. The results of RNA-seq indicated
that the agent induced significantly differential expression of genes
that are associated with defense response, stress response, autophagy,
and ubiquitination. Among them, 15 critical differential expressed
genes were selected for real-time quantitative PCR validation. We
further demonstrated that ε-PL can induce host defense responses
by assessing the activity of several defense-related enzymes in plants.
Our results provided valuable insights into molecular anti-viral mode
of action for ε-PL, which is expected to be applied as a novel
microbial natural product against plant virus diseases.