Integrated transcriptomic and metabolomic analyses of a wax deficient citrus mutant exhibiting jasmonic acid-mediated defense against fungal pathogens

Naturally, resistant crop germplasms are important resources for managing the issues of agricultural product safety and environment deterioration. We found a spontaneous mutant of 'Newhall' navel orange (Citrus sinensis Osbeck) (MT) with broad-spectrum protections against fungal pathogens in the orchard, postharvest-storage, and artificial inoculation conditions. To understand the defense mechanism of MT fruit, we constructed a genome-scale metabolic network that integrated metabolome and transcriptome datasets. The coordinated transcriptomic and metabolic data were enriched in two sub-networks, showing the decrease in very long chain fatty acid (by 41.53%) and cuticular wax synthesis (by 81.34%), and increase in the synthesis of jasmonic acid (JA) (by 95.23%) and JA-induced metabolites such as 5-dimethylnobietin (by 28.37%) in MT. Furthermore, cytological and biochemical analyses confirmed that the response to fungal infection in MT was independent of wax deficiency and was correlated with the levels of jasmonates, and the expression of plant defensin gene PDF1.2. Results of exogenous application of MeJA and JA inhibitors such as propyl gallate proved that JA-mediated defense contributes to the strong tolerance against pathogens in MT. Our results indicated that jasmonate biosynthesis and signaling are stimulated by the fatty acid redirection of MT, and participate in the tolerance of pathogenic fungi.