Systemic acquired resistance networks amplify airborne defense cues

Abstract

Salicylic acid (SA)-mediated innate immune responses are activated in plants perceiving volatile monoterpenes. Here, we show that monoterpene-associated responses are propagated in feed-forward loops involving the systemic acquired resistance (SAR) signaling components pipecolic acid, glycerol-3-phosphate, and LEGUME LECTIN-LIKE PROTEIN1 (LLP1). In this cascade, LLP1 forms a key regulatory unit in both within-plant and between-plant propagation of immunity. The data integrate molecular components of SAR into systemic signaling networks that are separate from conventional, SA-associated innate immune mechanisms. These networks are central to plant-to-plant propagation of immunity, potentially raising SAR to the population level. In this process, monoterpenes act as microbe-inducible plant volatiles, which as part of plant-derived volatile blends have the potential to promote the generation of a wave of innate immune signaling within canopies or plant stands. Hence, plant-to-plant propagation of SAR holds significant potential to fortify future durable crop protection strategies following a single volatile trigger.

The Ecology of Salicylic Acid Signaling: Primary, Secondary and Tertiary Effects with Applications in Agriculture

“…Repeated application of MeSA strengthened this response [149] suggesting that exogenous application in field settings could hold potential for managing pathogen resistance. Field wide applications of exogenous elicitors may not even be necessary; recent work showed that positive feedback loops involving SAR and monoterpene communication could potentially propagate SAR at the population level using plant–plant communication to magnify spatial effects [150]. Effects of exogenous elicitors could also be magnified through time across generations as epigenetic effects of exogenous elicitors have been documented and could potentially engender inter-generational defense with fewer applications [151].…”

Pieris brassicae eggs trigger interplant systemic acquired resistance against a foliar pathogen in Arabidopsis

“…4a). ALD1 was shown to be also required for Pst ‐induced production of volatile monoterpenes and volatile‐mediated interplant SAR triggered by Pst (Wenig et al ., 2019). Because we found that EE‐triggered interplant SAR also depends on functional ALD1 in the sender plant (Fig.…”

“…Strikingly, both ALD1 and FMO1 are required for the generation of egg‐induced interplant SAR signal, like the establishment of egg‐induced intraplant SAR (Hilfiker et al ., 2014). Similarly, Pst AvrRpm1 ‐triggered generation of interplant SAR‐inducing volatile signal depends also on ALD1 in the sender plants (Wenig et al ., 2019). It thus appears that a common mechanism is involved in the generation of intra‐ and interplant signals to trigger systemic immunity.…”

Metabolic profiling reveals local and systemic responses of kiwifruit to Pseudomonas syringae pv. actinidiae

“…Several compounds have been reported to participate in SAR long‐distance communication. These compounds included the putative lipid transfer protein DEFECTIVE IN INDUCED RESISTANCE1 (DIR1), the methyl ester of SA (MeSA), glycerol‐3‐phosphate (G3P), the diterpenoid dehydroabietinal, pipecolic acid, and the dicarboxylic acid azelaic acid (Wang et al., 2018; Wenig et al., 2019). Systemic effects of Psa infection were demonstrated by correlation‐based network analysis as well as independent component analysis.…”