Antifungal defences are upregulated as a systemic response to OGs
We further explored antifungal defence responses induced by OGs that may contribute to the enhanced pathogen resistance observed. Leucyl aminopeptidase (LAP) is a JA regulated, wound-responsive protein, displaying a dual role as aminopeptidase but also as a chaperone (Fowler et al., 2009, Scranton et al., 2012), and β-1,3-glucanases, are inducible enzymes with antimicrobial properties for their action on the β-glucans in fungal cell walls. LAP activity was induced only in distal leaves in response to leaf OG treatment (LT-SL), whereas no changes were observed locally in treated nor upon root treatment (Figure 5a). Total β-1,3-glucanase activity did not vary among the different treatments (suppl. Fig. S5). Several β-1,3-glucanases are present in tomato with differential regulation patterns, and total enzymatic activities may mask enhancement of specific glucanase isoforms. Thus, we examined the expression levels of GluB, encoding a β-1,3-glucanase, known to be inducible by JA, ET and pathogens (van Kan et al., 1992). WhileGluB expression was not induced in OG-treated leaves (Local response), it was boosted in leaves as a systemic response to OG treatments in both leaves or roots treatments (Fig. 5b). Note that the enhanced GluB expression correlates with the tissues showing OG induced resistance in the pathogen bioassay.
Taken together, our results suggest that the accumulation of defensive metabolites and the induction of pathogenesis-related proteins may underlie the efficient systemic protection against B. cinereainduced by OGs in tomato (Figure. 6).