Salicylic Acid Biosynthesis and Role in Modulating Terpenoid and Flavonoid Metabolism in Plant Responses to Abiotic Stress

Abstract

The phytohormone salicylic acid (SA) plays important roles in the regulation of responses to biotic and abiotic stress, as well as developmental processes, but the most extensive research has been focused on characterization of SA signaling in plant-microbial pathogen interactions. In response to pathogen infection, plants activate SA biosynthesis, which is essential for defense responses, such as PAMP (pathogen-associated molecular pattern)-triggered immunity (also known as basal resistance), effector-triggered immunity, and establishment of systemic acquired resistance. Studies revealed that Nonexpresser of Pathogenesis-Related protein 1 (NPR1), 3, and 4 are SA receptors, which are responsible for SA-mediated defense gene expression as well as regulation of cell fate in local infected tissues and systemic noninfected tissues. Defense gene expression is activated by SA mainly through NPR1, the activity of which is tightly regulated by cytoplasm-to-nucleus translocation and posttranslational modifications, such as phosphorylation, ubiquitination, and sumoylation. This chapter mainly summarizes advances concerning SA biosynthesis and signaling pathways.