A Shift in Auxin Homeostasis Is Linked to the Paclobutrazol-Induced Formation of Adventitious Roots in Chestnut

Abstract Vegetative propagation of chestnut relies on the formation of adventitious roots. However, the recalcitrant nature of this species hinders the development of new roots, establishing a bottleneck for industrial and research purposes. Auxin is involved in all aspects of the adventitious rooting process. Exogenous auxin application is mandatory to induce rooting in chestnut, although other phytohormones are known to be involved in the signaling events leading to root induction and growth. Gibberellins, which are essential for several developmental processes in plants, inhibit the formation of adventitious roots. In the present study we used physiological and molecular analyses to investigate the role of gibberellins and paclobutrazol (gibberellins-synthesis inhibitor) on the adventitious root formation in chestnut. When paclobutrazol was applied to chestnut microshoots in the absence of exogenous auxin, it led to the formation of adventitious roots, although in a lower frequency than with auxin treatment. Interestingly, the inductive effect of auxins was blocked when gibberellins were applied concomitantly with auxin. Our results indicate that gibberellins have a negative effect on adventitious rooting in chestnut, particularly through their control on the activity of the CsPIN1 gene. This study helps explain the role of gibberellins in the rooting process, the signaling mechanisms involved and the role played by auxin transporters.