Plant Small RNAs: Big Players in Biotic Stress Responses

Abstract

A myriad of small RNAs (18–25 nt in length) undergo heterogeneous modifications to inflect RNA stability and other complex physiological processes like stress responses, metabolism, immunity, and epigenetic inheritance of environmentally acquired traits. Such small RNAs include microRNAs (miRNAs), PIWI-interacting RNAs (piRNAs), small interfering RNAs (siRNAs), and tRNA-derived small RNAs (tsRNAs). Worldwide crop production and human health are affected when plants are attacked by pathogens and pests. Therefore, a large collection of genes get up- or down regulated to mediate the defense responses in plants against pathogens (bacteria, fungi, oomycetes, and viruses). Host endogenous small RNAs, thus, come into play to counter biotic stress where RNA silencing machinery is utilized to facilitate pathogen-associated molecular pattern-triggered immunity and effector-triggered immunity. RNA interference (RNAi) pathways trigger gene silencing in interacting species from even different kingdoms (cross-kingdom RNAi). Diverse pathways are involved in regulating the defense mechanism including Dicer-like proteins (DCLs), double-stranded RNA (dsRNA) binding protein, RNA-dependent RNA polymerases (RDRs), RNA polymerase IV and V, small RNA methyltransferase HEN1, and Argonaute (AGO) proteins showcasing their functional specificities as well as verbosity. Transgenic plants are newly emerging players that help in solving the problem of pathogen attack in fields. In this chapter, the recent breakthrough on the function of sRNAs in response to biotic stress, mainly in plant-pathogen interaction, and its application in disease control is discussed.