Gibberellins inhibit adventitious rooting in hybrid aspen and Arabidopsis by affecting auxin transport

Knowledge of processes involved in adventitious rooting is important to improve both fundamental understanding of plant physiology and the propagation of numerous plants. Hybrid aspen plants overexpressing a key gibberellin (GA) biosynthesis gene (AtGA20ox1) grow rapidly, but have poor rooting efficiency, which restricts their clonal propagation. Therefore, we investigated the molecular basis of adventitious rooting in Populus and the model plant Arabidopsis. Production of adventitious roots (ARs) in trees cuttings is initiated from the basal stem region, and involves the interplay of several endogenous and exogenous factors. Roles of several hormones in this process have been characterized, but effects of GAs have not been fully investigated. Here, we show that a GA treatment negatively affects numbers of adventitious roots produced by wild-type hybrid aspen cuttings. Furthermore, both hybrid aspen plants and intact Arabidopsis seedlings overexpressing AtGA20ox1, PttGID1.1 or PttGID1.3 genes (with a 35S promoter) produce few ARs, although ARs develop from basal stem region of hybrid aspen and hypocotyl of Arabidopsis. In Arabidopsis, auxin and strigolactones are known to affect ARs formation. Our data show that the inhibitory effect of GA treatment on adventitious rooting is not mediated by perturbation of the auxin signalling pathway or strigolactone biosynthetic and signalling pathways. Instead, GAs appear to act by perturbing polar auxin transport, in particular auxin efflux in hybrid aspen and both efflux and influx in Arabidopsis