Flavonoids and alkaloids biosynthetic genes are upregulated in tomato roots as a local and systemic response to OGs
Flavonoids and alkaloids, both accumulated in response to OGs, are phenylpropanoids derivatives that significantly contribute to plant resistance (Treutter 2005; Mithöfer and Boland 2012). To gain further insight into the regulation of flavonoids and alkaloids in response to OGs, we studied changes in the expression of relevant biosynthetic genes at the local and systemic level 6 h after leaf or root treatment (Table 3). For the analysis, we chose PHENYLALANINE AMMONIA LYASE(PAL), involved in the first step in the phenylpropanoid biosynthetic pathway, CHALCONE SYNTHASE 1 (CHS .1 ), encoding the first enzyme of the flavonoid biosynthetic pathway that produces naringenin chalcone, CHALCONE ISOMERASE 1 (CHI1 ), responsible for the downstream reaction that converts naringenin chalcone to naringenin, and PUTRESCINE N-METHYLTRANSFERASE (PMT) , encoding a key enzyme in the biosynthesis of tropane alkaloids (Biastoff et al., 2009; Petrussa et al., 2013).
In leaves, none of those genes showed altered expression levels in response to OGs at 6 hpt regardless the OG application site. No expression of PMT was detected in leaves. In contrast, the expression of these genes showed significant changes in roots both as a local and a systemic response to the treatment. All these marker genes except CHS1 were induced in roots as a systemic response to OG treatment in leaves (LT-Root). Remarkably, all four genes were strongly upregulated locally upon root treatment, with a particularly strong effect for CHS1 (75 fold). These results are in agreement with the metabolic analyses and collectively evidence the key role of roots in flavonoid and alkaloid biosynthesis following OG perception (Table 3).