A small peptide enhances cotton salt tolerance via MPK3/6 activation: Functional discovery of GhPIPL7 in salt stress signaling

Cotton (Gossypium spp.) production is increasingly threatened by soil salinization, yet the roles of endogenous peptide regulators in salt stress responses remain largely unexplored. INFLORESCENCE DEFICIENT IN ABSCISSION (IDA)/IDA-Like (IDL) and PAMP-INDUCED SECRETED PEPTIDE (PIP)/PIP-Like (PIPL) peptides have been implicated in plant development and stress adaptation, but their specific functions in cotton are unclear. We hypothesized that certain IDA/IDL and PIP/PIPL peptides enhance salt tolerance by modulating stress-responsive signaling pathways. To test this, we identified 63 IDA/IDL and 29 PIP/PIPL genes across four Gossypium species and analyzed their gene structures, chromosomal distribution, promoter elements, and expression profiles under abiotic stress. In G. hirsutum, GhIDL02 and GhPIPL7 showed strong induction by salt stress. Functional validation via virus-induced gene silencing (VIGS) and exogenous peptide application revealed that both peptides enhance salt tolerance by improving Na⁺/K⁺ homeostasis. Transcriptomic and molecular analyses further demonstrated that GhPIPL7 confers salt tolerance by activating mitogen-activated protein kinases 3 and 6 (MPK3/6) signaling. These findings uncover a peptide-mediated regulatory mechanism of salt stress and identify GhPIPL7 as a promising candidate for molecular breeding, highlighting the potential of endogenous small peptides as targets for improving salt resilience in cotton.