An update on salicylic acid biosynthesis, its induction and potential exploitation by plant viruses.

Salicylic acid (SA) is a plant hormone essential for effective resistance to viral and non-viral pathogens. SA biosynthesis increases rapidly in resistant hosts when a dominant host resistance gene product recognizes a pathogen. SA stimulates resistance to viral replication, intercellular spread and systemic movement. However, certain viruses stimulate SA biosynthesis in susceptible hosts. This paradoxical effect limits virus titer and prevents excessive host damage, suggesting that these viruses exploit SA-induced resistance to optimize their accumulation. Recent work showed that SA production in plants does not simply recapitulate bacterial SA biosynthetic mechanisms, and that the relative contributions of the shikimate and phenylpropanoid pathways to the SA pool differ markedly between plant species.Work by AMM and JPC was supported by grants from UK Biotechnological and Biological Sciences Research Council (SCPRID grant number BB/J011762/1, and GCRF grant number BB/P023223/1). Work by TZ was supported by grants from the Ministry of Agriculture and Rural Affairs of China (2018YFD020062, 2016ZX08010-001), the National Natural Science Foundation of China (31371912) and a grant from the Ministry of Education of China (the 111 Project B13006)