Peptides are important regulators that participate in the modulation of almost every physiological event in plants, including defense. Recently, many of these
peptides have been described as defense elicitors, termed phytocytokines, that are released upon pest or pathogen attack, triggering an amplification of plant defenses. However, little is known about
peptides sensing and inducing resistance activities in heterologous plants. In the present study, exogenous
peptides from solanaceous species, Systemins and HypSys, are sensed and induce resistance to the necrotrophic fungus Plectosphaerella cucumerina in the taxonomically distant species Arabidopsis thaliana. Surprisingly, other
peptides from closer taxonomic clades have very little or no effect on plant protection. In vitro bioassays showed that the studied
peptides do not have direct antifungal activities, suggesting that they protect the plant through the promotion of the plant immune system. Interestingly, tomato
Systemin was able to induce resistance at very low concentrations (0.1 and 1 nM) and displays a maximum threshold being ineffective above at higher concentrations. Here, we show evidence of the possible involvement of the JA-signaling pathway in the
Systemin-Induced Resistance (Sys-IR) in Arabidopsis. Additionally,
Systemin treated plants display enhanced BAK1 and BIK1 gene expression following
infection as well as increased production of ROS after
PAMP treatment suggesting that
Systemin sensitizes Arabidopsis perception to pathogens and
PAMPs.