Abstract
Salicylic acid (SA) is an important plant hormone with a critical role in plant defense against pathogen infection. Despite extensive research over the past 30 year or so, SA biosynthesis and its complex roles in plant defense are still not fully understood. Even though earlier biochemical studies suggested that plants synthesize SA from cinnamate produced by phenylalanine ammonia lyase (PAL), genetic analysis has indicated that in Arabidopsis, the bulk of SA is synthesized from isochorismate (IC) produced by IC synthase (ICS). Recent studies have further established the enzymes responsible for the conversion of IC to SA in Arabidopsis. However, it remains unclear whether other plants also rely on the ICS pathway for SA biosynthesis. SA induces defense genes against biotrophic pathogens, but represses genes involved in growth for balancing defense and growth to a great extent through crosstalk with the growth-promoting plant hormone auxin. Important progress has been made recently in understanding how SA attenuates plant growth by regulating the biosynthesis, transport, and signaling of auxin. In this review, we summarize recent progress in the biosynthesis and the broad roles of SA in regulating plant growth during defense responses. Further understanding of SA production and its regulation of both defense and growth will be critical for developing better knowledge to improve the disease resistance and fitness of crops.
Highlights
Salicylic acid (SA) is produced by many prokaryotic and eukaryotic organisms including plants
More than 40 year ago, it was reported that the application of exogenous SA triggers immune-like responses in plants characterized by induced production of plant-pathogenesis-related (PR) proteins and induces disease resistance [3]
Silencing of five phenylalanine ammonia lyase (PAL) isoforms or two IC synthase (ICS) isoforms is effective in suppressing SA biosynthesis and compromising disease resistance [24]. These results indicate that the PAL and ICS pathways are important for pathogen-induced
Summary
Salicylic acid (SA) is produced by many prokaryotic and eukaryotic organisms including plants. With the established role of SA in plant immunity, there has been extensive research over the past 30 year to understand the molecular basis for SA-mediated immune responses. Recent progress has been made in identifying the critical components in the ICS pathway for SA biosynthesis in the model plant Arabidopsis [10,11]. It remains to be determined whether different plants rely on the ICS, PAL, or both pathways for SA biosynthesis. We review recent progress in the research on SA biosynthesis and the emerging roles of SA in regulating plant growth with a particular focus on its crosstalk with auxin under stress conditions
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