Stories of Salicylic Acid: A Plant Defense Hormone

Salicylic acid (SA) is a key plant hormone required for establishing resistance to many pathogens. SA biosynthesis involves two main metabolic pathways with multiple steps: the isochorismate and the phenylalanine ammonia-lyase pathways. Transcriptional regulations of SA biosynthesis are important for fine-tuning SA level in plants. We highlight here recent discoveries on SA biosynthesis and transcriptional regulations of SA biosynthesis. In addition, SA perception by NPR proteins is important to fulfil its function as a defense hormone. We highlight recent work to give a full picture of how NPR proteins support the role of SA in plant immunity. We also discuss challenges and potential opportunities for future research and application related to the functions of SA in plants.