Transcriptomic and biochemical analysis of highlighted induction of phenylpropanoid pathway metabolism of citrus fruit in response to salicylic acid, Pichia membranaefaciens and oligochitosan

The effects of salicylic acid (SA), Pichia membranaefaciens and oligochitosan on induction of disease resistance in citrus fruit were investigated using transcriptomic and biochemical analysis in this study. The results of disease incidence and lesion diameter showed that application of exogenous elicitors SA (2.5 mmol L−1), P. membranaefaciens (1 × 108 cells mL−1) or oligochitosan (15 g L−1) were all effective in inhibiting blue and green molds in citrus fruit. Transcript profiling analysis of citrus fruit peel tissues revealed more differentially expressed genes in phenylpropanoid pathway metabolism induced by the three elicitors compared with other biological pathways. Moreover, biochemical analysis demonstrated that the three elicitors effectively enhanced phenylpropanoid pathway-related enzyme activities and stimulated the synthesis of phenolic acids and their subsequent metabolite lignin. Therefore, global results indicated that the activation of the phenylpropanoid biosynthesis pathway plays an important role in the induction of resistance in citrus fruit by the three elicitors.