Broccoli plant elicitor peptide BoPep4 enhances plant salt tolerance by improving glucosinolate metabolism

Plant elicitor peptides (Peps), derived from precursor proteins PROPEPs, function as plant peptide hormones regulating abiotic stress tolerance. However, the underlying metabolic mechanisms remain incompletely understood. Here, we show that overexpression of BoPROPEP4 in Arabidopsis and broccoli hairy roots enhances salt tolerance, as evidenced by improved phenotypic performance, increased chlorophyll levels, optimized Na⁺/K⁺ ratios, reduced H₂O₂ levels, and elevated antioxidant enzyme activities. Salt stress induces the upregulation of salt-responsive genes in transgenic lines and triggers the in vivo cleavage of BoPROPEP4 into the mature peptide BoPep4. Transcriptomic analysis reveals that BoPep4 modulates glucosinolate metabolism in broccoli, leading to increased accumulation of aliphatic and indole glucosinolates and their bioactive derivatives sulforaphane and indole-3-carbinol under salt stress. Furthermore, exogenous BoPep4 application to salt-stressed broccoli upregulates the expression of genes involved in glucosinolate biosynthesis and degradation, increases GSH content via sulfur reallocation from glucosinolate degradation, and boosts antioxidant enzyme activities. Genetic validation through virus-induced gene silencing of BoPROPEP4 and BoPEPR2 in broccoli demonstrates reduced glucosinolate levels and compromised salt tolerance. In Arabidopsis, the protective effect of BoPep4 against salinity is diminished in glucosinolate-degradation mutants (pen2 and tgg1/2), highlighting the importance of functional glucosinolate metabolism in BoPep4-mediated salt adaptation. This study uncovers a novel metabolic mechanism underlying peptide-mediated salt tolerance and provides a potential approach for enhancing crop salt tolerance.