OsRIBONUCLEASE1-induced rRNA breakdown enhances rice root growth and phosphate use efficiency

Phosphorus (P) management has long been a challenge in agriculture, particularly improving P use efficiency (PUE) in crop plants, including rice. Although several studies have documented enhanced PUE in rice varieties, the underlying molecular mechanisms remain poorly understood, hindering crop engineering efforts. In this study, we expressed the rice ribonuclease 1 (OsRNS1) gene, which encodes a Class I monocot-specific ribonuclease, throughout the root under P deficiency, which was confirmed via green fluorescent protein and histochemical β-glucuronidase assays. Notably, the OsRNS1 protein localized in the cell wall and endoplasmic reticulum. Overexpression of OsRNS1 promoted ribosomal RNA (rRNA) degradation and PUE, while knockout of OsRNS1 reduced rRNA degradation. Moreover, OsRNS1 overexpression, driven by a root-preferred promoter, enhanced tolerance to P-deficiency stress compared with the wild type. OsRNS1 was regulated by the rice PHOSPHATE STARVATION RESPONSE 2 protein, and changes in OsRNS1 transcript levels influenced the expression of other acid phosphatase and phosphate transporter genes. Collectively, these findings indicate that OsRNS1, a P deficiency-induced ribonuclease, regulates P homeostasis via rRNA degradation during P-deficiency stress. This molecular mechanism of P-deficiency tolerance holds promise for biotechnological applications aimed at developing rice varieties with improved PUE.