Defective RNA particles of Tomato black ring virus: origin, structure and biological effect

Abstract

Resumen del trabajo presentado a la Conferencia Power of Viruses, celebrada en Poreč (Croatia) del 16 al 18 de mayo de 2018.Tomato black ring virus (TBRV) infects a wide range of economically important plants, and is distributed worldwide. The genome of TBRV consists of two single stranded RNAs of positive polarity. Both RNAs contain a small protein VPg at their S' ends and have polyadenylated 3' ends. RNA1 is responsible for viral replication and polyproteins' processing and RNA2 for encapsidation and movement in plant. The TBRV infection can be accompanied by subviral particles such as satellite or defective RNAs. Defective RNA particles are deletion/and/or rearrangement variants of the viral genomes created during replication. The presence of subviral RNAs might have a great impact on viral replication, accumulation and symptoms observed on infected plants. D RNAs which are referred to interfere with multiplication of their helper viruses are called defective interfering RNAs (DI RNAs). TBRV is the only member of the Nepovirus genus that is known to form defective RNA particles (D RNAs) during replication. In this study, we analyzed the origin and structure of D RNAs generated de novo during prolonged passages of TBRV isolates in Chenopodium quinoa plants. Moreover, the effect of D RNAs on helper virus replication and symptoms observed on infected plants was estimated. Two TBRV isolates, originated from Solanum lycopersicum and Lactuca sativa, were serially passaged in C. quinoa and after 1S passages the purified viral preparations were obtained. Viral RNA was isolated using phenol-chloroform method. The analysis of RNA profile revealed the presence of short, D RNA molecules. D RNAs were amplified and sequenced, and obtained sequences were compared with the helper virvs genome. C. quinoa, S. lycopersicum and Nicotiana tabacum were infected.with TBRV+D RNA and TBRV-D RNA. The symptoms and viral accumulation were manito red 7, 14, 21, and 28 dpi. The accumulation level of TBRV in each host was measured by RT-qPCR and statistical analyses were performed. The analysis revealed that D RNAs derived by interna! deletion in the RNA1 molecule of TBRV and contained a portian of S' non-coding region, a fragment of polymerase gene and almost entire 3' non-coding region. Plants infected with TBRV+D RNA displayed milder symptoms in comparison to those infected with TBRV-D RNA. Statistical analyses confirmed that D RNAs interfere with TBRV replication and thus should be referred to as defective interfering particles.Peer reviewe