Function of Mediator in Regulating Salicylic Acid Mediated Signaling and Responses in Plants

Abstract

AbstractMediator is a transcriptional co-regulator required for the transcription of all protein coding genes by RNA polymerase II (RNA pol II) in eukaryotes including plants. Mediator is a complex of around 30 subunits and transmits the signals from promoter bound transcription factors to the RNA pol II. The Mediator is composed of head, middle and tail modules which constitute the core mediator complex to which a forth kinase module is reversibly associated. In plants, phytohormones play an essential role in all stages of growth and development from embryogenesis to flowering as well as response to diverse biotic and abiotic environmental factors by activation of several signaling cascades. Every signaling cascade regulates a large array of genes through a network of transcription factors (TFs). All TFs have to interact with one or more mediator subunits to regulate the corresponding gene expression. Hence, Mediator plays an essential part in orchestrating the transcriptional output of all signaling cascades. Salicylic acid (SA) is a phenolic hormone with important role in plant growth and development as well as critical function in resistance against pathogens. SA has been found to be an essential part of plant innate immune system required for the pattern -triggered immunity (PTI), Effector-triggered immunity (ETI) as well as for the establishment of systemic acquired resistance (SAR). Functional studies of several mediator subunit mutants revealed that different aspects of SA signaling from its biosynthesis to activation of downstream PR gene expression and SAR are regulated by mediator subunits from the middle, tail and kinase modules of Mediator. In this chapter, we will discuss in detail how the Mediator plays a key role in regulating SA mediated signaling and defense responses in plants.KeywordsMediator complexTranscriptional regulationPlant-pathogen interactionsPlant defense and NPR1