Stress-induced volatile (E)-2-hexenal activates strawberry disease resistance through the temporal accumulation of phenolic compounds and terpenoids

Plant organs, especially fruit, synthesize a variety of volatile organic compounds (VOCs) that crucial for pathogen defense. This study identified (E)-2-hexenal as a key early-response VOC in strawberries-Botrytis cinerea interactions and analyzed its defensive role. B. cinerea infection induced a increase in (E)-2-hexenal production and a 1.90-fold increase of Hexenal isomerase (HI) expression. FaHI was identified as the key synthetic gene through homologous sequence analysis and validated by transient overexpression, which increased FaHI transcript levels by 3.55-fold. A fumigation model was constructed to explore the (E)-2-hexenal-induced resistance. At 1 μM concentration, (E)-2-hexenal showed the strongest antifungal effect, reducing lesion diameter to 57 % of the control. Integrated physiological, biochemical, metabolomic and transcriptomic analyses demonstrated increased activities of defense enzymes such as β-1,3-glucanase, chitinase, phenylalanine ammonia lyase, and polyphenol oxidase, alongside the biosynthesis activation of 31 phenolic compounds and 7 terpenoids. Furthermore, the temporal accumulation profiles of monoterpenoids, flavonoids, triterpenoids, phenolic acids and phenolic derivatives were characterized, revealing dynamic defense response to (E)-2-hexenal priming. These findings elucidate the signaling role of (E)-2-hexenal in regulating resistance, identify FaHI as the target gene for breeding disease-resistant varieties, and demonstrate the potential of (E)-2-hexenal as a natural alternative fungicide for postharvest disease management.