Chapter 11 - RNA silencing as a general defence mechanism against pathogens

Abstract

The chapter focuses on the general mechanism of RNA silencing in plants, plant viral suppressor proteins of RNA silencing, and applications in plant breeding. The most important feature of RNA silencing is the formation of small interfering RNAs (siRNAs) of 21–23 bp in length. The chapter also explains the coexistence and discovery of RNA silencing and its key characteristics and triggers, which include early events in triggering RNA silencing; virus infection, cross-protection, and RNA silencing; and transitive RNA silencing. Virus infection is an efficient trigger of RNA silencing particularly if viruses share sequence homology with nuclear genes. Some of the topics that the chapter discusses are suppression of RNA silencing by plant virus-encoded proteins, RNA silencing in plant breeding, and techniques used to analyze viral suppressor activity. On the basis of suppressor protein activity, virus-derived RNA silencing suppressor proteins can be assigned to four groups. Various techniques have been used to dissect the mechanism of plant viral suppressors in RNA silencing. This is reflected by the fact that various suppressor proteins have different modes of action, and they can be classified into three groups. The suppressor can be introduced either into target cells subject to silencing together with the trigger or into silenced tissues to reverse silencing in a process called agroinfiltration. Most of the transient silencing suppressor assays have been identified based on their ability to interfere with the local and systemic silencing of the green fluorescent protein gene (GFP) in GFP-transgenic Nicotiana benthamiana plants in an agroinfiltration assay.