Hydrogen sulfide enhances resistance to Penicillium italicum by activating phenylpropanoid metabolism in postharvest navel orange fruit

An effective prevention treatment in postharvest fruit diseases is helpful in maintaining fruit quality and prolonging shelf life. In this study, we aimed to investigate whether hydrogen sulfide (H2S) enhances resistance to Penicillium italicum by activating phenylpropanoid metabolism in postharvest navel orange fruit. The findings showed that 25 μL/L H2S fumigation alleviated the disease symptoms and lesion area of P. italicum-inoculated navel orange fruit. RTqPCR analysis revealed that H2S treatment upregulated the transcription levels of phenylpropanoid biosynthesis (CitC4H, Cit4CL, CitCYP98A, CitCAD, CitCHI, and CitCHS) and metabolite-related genes (CitPAL, CitGLU, CitPOD, and CitCSE). Meanwhile, H2S upregulated the transcripts of MYB and WRKY transcription factors and had similar expression patterns to phenylpropanoid metabolism-related genes. Correlation analysis showed that H2S-promoted accumulation patterns of total phenols, flavonoids, and lignin were positively correlated with phenylpropanoid metabolism-related gene transcripts. In addition, sodium hydrosulfide (NaHS, H2S donor)-released H2S restrained P. italicum mycelium growth. Treatment with 25 and 50 mmol/L NaHS markedly decreased the mycelium weight while increasing extracellular conductivity and membrane leakage. Overall, these findings indicated that H2S could induce resistance in navel orange fruit because of its inhibitory role and positive regulation of many phenylpropanoid metabolism-modifying genes as well as possibly candidate MYB and WRKY transcription factors.