Strigolactone enhances aluminium tolerance in rice ( Oryza sativa L. ) by modulating nitric oxide production and cell wall aluminium sequestration

BACKGROUND AND AIMS: Aluminium (Al) toxicity is a major barrier to rice yield in acidic soils, yet the hormonal mechanisms underlying Al tolerance remain incompletely understood. Strigolactones (SLs) have recently been identified as key regulators of plant adaptation to abiotic stress, but their involvement in Al tolerance has not been clearly defined. METHODS: Using rice (Oryza sativa L.) seedlings, we investigated Al-induced changes in endogenous SL accumulation and examined the effects of pharmacological activation of SL signalling with the synthetic analogue GR24 on root growth, Al accumulation, cell wall composition, gene expression and nitric oxide (NO) production under Al stress. KEY RESULTS: Al exposure rapidly stimulated endogenous SL accumulation in rice roots by approximately 10 %. Activation of SL signalling by GR24 significantly alleviated Al-induced inhibition of root elongation by 20 % and decreased Al content in root tips by 29 %. GR24 treatment under Al stress altered root cell wall properties by decreasing hemicellulose- and pectin-associated Al sequestration and attenuated the transcriptional activation of key Al-responsive genes, including OsART1 (Oryza sativa ALUMINUM RESISTANCE TRANSCRIPTION FACTOR 1), citrate transporter genes OsFRDL2 and OsFRDL4 (Oryza sativa FRD3-LIKE PROTEIN 2/4) and the Al transporter gene OsNRAT1 (NRAMP ALUMINUM TRANSPORTER 1). Notably, GR24-enhanced Al tolerance was accompanied by elevated accumulation of NO in root tips, and disruption of NO signalling abolished the protective effects of GR24. CONCLUSIONS: This research confirms that SL signalling plays a previously unrecognized role in rice Al tolerance by coordinating NO-dependent regulation of cell wall Al sequestration and Al-responsive gene expression. This study provides new insight into the hormonal control of plant adaptation to acidic soils.