Phytocytokines are endogenous danger
peptides that are actively released after a pest or pathogen attack, triggering an amplification of plant immune responses. Here, we found that
Systemin, a
peptide from tomato, has a substantial impact at the molecular level in Arabidopsis plants that leads to induced resistance against Plectosphaerella cucumerina. Using transcriptional and metabolomics approaches, and loss-of-function mutants to analyse the molecular mechanisms underlying induced resistance against the necrotroph, we decipher the enhanced molecular responses in
Systemin-treated plants following
infection. Some
protein complexes involved in the response to other damage signals, including the BAK1-BIK1
protein complex and
heterotrimeric G proteins, as well as MPK activation, were among the early signalling events triggered by
Systemin in Arabidopsis upon
infection. Non-targeted analysis of the late responses underlying
Systemin-Induced Resistance1 (Sys-IR) showed that phenolic and indolic compounds were the most representative groups in the
Systemin metabolic fingerprint. Lack of
flavonoids resulted in the impairment of Sys-IR. On the other hand, some indolic compounds showed a priming profile and were also essential for functional Sys-IR. Evidence presented here shows that plants can sense heterologous
peptides from other species as danger signals driving the participation of common
protein cascades activated in the PTI and promoting enhanced resistance against necrotrophic fungus.