Mobile Signaling Peptides: Secret Molecular Messengers with a Mighty Role in Plant Life

Adaptive mechanisms for unfavorable environments have evolved in plants for thousands of generations, primarily in the form of endogenous chemical signals and the coordination of physiological processes. Signaling peptides (SPs) are diverse molecular messengers in various stress responses which have been identified in different plant families. SPs are recognized by the membrane-localized receptors and co-receptors, leading to downstream signaling for various plant responses. Progress in in silico analysis, along with other factors, has increased our understanding of the signaling peptide-mediated regulatory mechanisms underlying the entire plant life cycle. SPs mediate both long-distance (root-to-shoot-to-root) and local cell–cell communication via vascular system to communicate and coordinate with plant organs at distant locations. During abiotic stress, SPs inside plant cells perceive stress signals and transfer information at short and long physiological ranges through the signal transduction pathway, causing stress-responsive gene expression. SPs interact with pathogens and mediate cell-to-cell communication via signaling pathways. There are intriguing relationships between phytohormones and the secondary signaling cascades which are mediated by SPs. During biotic or abiotic stress, different peptides trigger jasmonic acid, ethylene, and ABA signaling, involving several secondary messengers. These messengers mediate the stress response via shared signaling components of ROS, Ca²⁺, and MAPKs, and they modify the gene expression for different phytohormones. In this review, we highlight current knowledge on the role of signaling peptides in plant adaptation, growth, and development. We aim to analyze the SP-receptor interactions and the significance of crosstalk between a few sample SPs and phytohormones. Potential directions on how scientists can use this information for crop improvement are also suggested.