Fatty acid metabolism and C9 aldehyde biosynthesis are involved in ε-poly-l-lysine-induced citrus fruit resistance to Penicillium digitatum.

Citrus fruit were easily infected by Penicillium digitatum, and caused green mold rapidly, resulting in enormous post-harvest losses. ε-poly- l -lysine (ε-PL) was generally regarded as a safe (GRAS) substance. Besides, it was proved to have a dual effect on harming fungi and triggering fruit defense responses. Fatty acid metabolism is closely related to fruit defense response. However, little is known about how ε-PL affected fatty acid metabolism in citrus fruit. Here, we found that ε-PL increased the expression of CsFATA , CsACSL , CsFAD2 , CsFAD3 , CsLOX2S , and CsHPL in fatty acid metabolism, decreasing oleic acid levels and enhancing linoleic and linolenic acid levels. Additionally, ε-PL enriched the activities of LOX and HPL during the oxidative decomposition of fatty acids, and activating C 9 aldehyde biosynthesis. Interestingly, ε-PL combined with (2E,4E)-nonadienal (C 9 aldehyde) would improve the inhibitory effect against Penicillium digitatum. And the combined bio-fungicide significantly delayed the citrus green mold compared to single concentrations of the individual components. These results suggested that ε-PL improved citrus fruit defense responses through fatty acid-mediated defense responses. Combined bio-fungicide consisting of ε-PL and (2E,4E)-nonadienal have an excellent prospect for controlling citrus green mold. [Display omitted] • ε-PL improved the genes expression related to fatty acid metabolism. • ε-PL decreased oleic acid levels and enhanced linoleic and linolenic acid levels. • ε-PL promoted the biosynthesis of (2E)-nonenal and (2E,4E)-nonadienal. • ε-PL combined with (2E,4E)-nonadienal could inhibit P. digitatum synergistically. [ABSTRACT FROM AUTHOR]