Buckwheat FeAUR3 enhances drought tolerance via a melatonin feedback loop

Aurora kinases are pivotal regulators of cell division, yet their roles in plant abiotic stress responses remain largely unexplored. While melatonin is a well-established protectant against drought, the upstream genetic pathways governing its biosynthesis under stress are not fully understood, limiting our ability to engineer robust drought tolerance. Here, we identify the buckwheat Aurora kinase, FeAUR3, as a critical upstream regulator of the melatonin-mediated drought response. In transgenic Arabidopsis, overexpression lines exhibited a marked enhancement in antioxidant capacity, with superoxide dismutase (SOD) and peroxidase (POD) activities increasing by up to 3.75-fold and 3.35-fold, respectively, alongside a 66.14% increase in proline accumulation and a 37.50% reduction in H₂O₂ content. Similarly, in buckwheat hairy roots, FeAUR3 overexpression strongly activated the antioxidant system, elevating SOD activity by up to 7.50-fold. Mechanistically, the nucleus-localized FeAUR3 directly upregulates the expression of melatonin biosynthesis genes FeAANAT and FeHIOMT, leading to a 23.6% elevation in endogenous melatonin levels, which initiates a coordinated defense response. Furthermore, we discovered that melatonin acts as an upstream positive regulator, further inducing FeAUR3 expression (by 1.12-fold under drought) to form a positive feedback loop that amplifies stress signaling. Molecular docking and dynamics simulations confirmed that melatonin stably binds to FeAUR3 with high affinity (binding energy: -7.2 kcal mol^-1). In summary, this study elucidates a FeAUR3-melatonin regulatory module that orchestrates drought adaptation in plants via a synergistic positive feedback loop and a dual defense mechanism. Our findings extend the functional paradigm of Aurora kinases into abiotic stress biology and establish FeAUR3 as a mechanistically validated target for engineering drought-resilient crops.