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).