Altered gibberellin metabolism in NCED OE rootstocks
In own-rooted plants, GA deactivation genes were induced in SP12 roots under control conditions, but moderate salinity alleviated this compared to WT plants (Martínez-Andújar et al. 2020b). Similarly, theGA2ox-3 (Solyc01g079200) gene (GA deactivation) was downregulated in SP5 and SP12 rootstocks. The different interactions between the SP lines could be explained by the different effects on ERF s, since 6/9 genes were up-regulated in SP5 and only 3/9 in SP12. ERFsinduce GA2oxidases to inactivate GAs, while ABA-dependent stabilization of DELLA proteins that inhibit GA signalling (Julkowska & Testerink 2015), would be alleviated in NCED OE grafts, probably due to the reduced ABA sensitivity. Interestingly, while this differential regulation may explain local root growth response, a systemic GA signal could also transferred to the scion since NCED OE rootstocks significantly increased xylem sap GA3 concentrations in the fruit trusses, consistent with the elongated truss phenotype observed (Figure 1).