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).