Gene Silencing without DNA: RNA-Mediated Cross-Protection between Viruses

TLDR

Upper leaves of plants infected with nepoviruses and caulimoviruses are symptom‑free and contain reduced virus levels. The authors show that RNA‑mediated defense is a general response to virus infection by analyzing plants infected with viruses distinct from nepoviruses or caulimoviruses. Transient gene expression assays revealed that RNA‑mediated cross‑protection is functionally equivalent to post‑transcriptional gene silencing. The study found that RNA‑mediated cross‑protection occurs with tobravirus infection leading to recovery, with potexvirus infection leading to cross‑protection without recovery, and that this mechanism is equivalent to post‑transcriptional gene silencing, indicating a broad natural defense against diverse viruses.

Abstract

Previously, it was shown that the upper leaves of plants infected with nepoviruses and caulimoviruses are symptom free and contain reduced levels of virus. These leaves are said to be recovered. Recovery is associated with RNA-mediated cross-protection against secondary virus infection. Here, by analyzing plants infected with viruses that are quite distinct from the nepovirus or caulimovirus groups, we demonstrate that this RNA-mediated defense is a general response to virus infection. Upon infection with a tobravirus, plants exhibited RNA-mediated cross-protection and recovery, as occurs in nepovirus-infected plants. However, upon infection with a potexvirus, plants exhibited RNA-mediated cross-protection without recovery. In both instances, a transient gene expression assay showed that RNA-mediated cross-protection was functionally equivalent to post-transcriptional gene silencing. Combined, these data provide direct evidence that post-transcriptional gene silencing of nuclear genes is a manifestation of a natural defense mechanism that is induced by a wide range of viruses.