Gibberellin-deactivating GA2OX enzymes act as a hub for auxin-gibberellin crosstalk in Arabidopsis thaliana root growth regulation

Abstract

Plant bodies are built from immobile cells, making the regulation of cell expansion essential for growth, development, and adaptation. In roots, cell elongation executes the movement of the root tips through soil. This process is tightly controlled by numerous signaling pathways. Among these, gibberellin and auxin signaling stand out for their contrasting effects on root growth, interacting through complex crosstalk at multiple regulatory levels. Here we reveal the molecular basis of the auxin-gibberellin crosstalk in the model plant Arabidopsis thaliana. We show that auxin signaling pathway steers the expression of GIBBERELLIN 2-OXIDASES (GA2OX), key gibberellin-deactivating enzymes in the root elongation zone. GA2OX are negative regulators of root cell elongation; GA2OX8 overexpression decreases gibberellin levels and inhibits root cell elongation, in contrast, the ga2ox heptuple mutant roots show elevated gibberellin levels in the elongation zone and grow longer roots. Shoot derived auxin can regulate GA2OX8 expression in roots, linking systemic auxin signaling to local gibberellin modulation. In addition, GA2OX8 is active in vascular tissues and the stem cell niche, tissues with high auxin levels. Loss of GA2OX genes results in altered stem cell niche, including increased quiescent center size and expanded root cell layers, highlighting the role of these enzymes in maintaining tissue organization. Together, our findings identify GA2OX6 and GA2OX8 enzymes as key mediators of auxin-gibberellin crosstalk, providing insights into their roles in root elongation, vascular development, and stem cell niche maintenance. These results expand our understanding of how auxin integrates with gibberellin signaling to coordinate root development and growth dynamics.