Systemin peptide application improves tomato salt stress tolerance and reveals common adaptation mechanisms to biotic and abiotic stress in plants

Plants are continuously challenged by several environmental stresses that impair their growth and production performances. Stresses encountered by plants can be caused by biotic agents (e.g., herbivores, parasitic microorganisms, weeds) and abiotic factors (e.g., cold, drought, soil and water salinity). Despite these differences, plants respond to biotic and abiotic stresses with shared adaptive mechanisms resulting in complex and interlinked cross-talks. Systemin is a hormone peptide, playing a central role in the regulation of plant response against a wide range of stress agents, including wound, phytopathogenic fungi and phytophagous and sucking insects. It has also been shown that upregulation of prosystemin, the precursor protein of systemin, enhanced the tolerance of tomato plants to salt stress, indicating that systemin induced molecular adaptations to biotic stress can also be beneficial to plants exposed to salt stress. Considering that systemin is a small peptide that can be sensed by plants both as soil drench and foliar applications, we hypothesized that exogenous applications of systemin may increase salt stress tolerance in tomato plants through the activation of multiple adaptation mechanisms. Here we report that a soil drench picomolar solution of systemin increases tomato salt stress tolerance by i) activating of SOS1, NHX and HKT Na+ transporters in leaves ii) enhancing the cellular antioxidant power, and iii) balancing the protease activity induced by salt stress. Activation of these responses upon exogeneous application of systemin was highly correlated to an improved tomato growth under salt stress, suggesting that systemin may represent an important component of the crosstalk between biotic and abiotic stress responses in plants.