Molecular Dialogue Across Kingdoms: The Role of Trans-Kingdom Peptides in Plant-Associated Interactions

Small signaling peptides have emerged as central mediators of biological communication within and between species. In this review, we propose and define the concept of trans-kingdom peptides (TKPs) as short, bioactive peptides produced by one organism that exert specific physiological effects in another, often across taxonomic kingdoms. We summarize recent progress in identifying plant- and microbe-derived TKPs that function in symbiosis, parasitism, plant-microbe interactions, herbivory, and host-virus dynamics. TKPs modulate host defense, developmental programs, microbial community structure, and abiotic stress responses through highly specific interactions with conserved receptor systems. We highlight known peptide families mediating legume-rhizobia nodulation, nematode parasitism, and microbial immune suppression, as well as newly discovered viral- and insect-derived peptides that manipulate plant immunity. We discuss how they shape coevolutionary dynamics between hosts and interacting organisms. Finally, we outline current challenges and potential applications of TKPs in agriculture, biomedicine, synthetic biology, and environmental sustainability. Altogether, by framing their emerging properties and biological significance, we aim to provide a conceptual foundation and encourage interdisciplinary research into this expanding frontier of plant biology and inter-organismal communication.