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<i>Low Phosphate Root</i> (<i>LPR</i>) encodes a protein localized to the endoplasmic reticulum (ER) and cell wall. This gene plays a key role in responding to phosphate (Pi) deprivation, especially in remodeling the root system architecture (RSA). An identification and expression analysis of the <i>OsLPR</i> family in rice (<i>Oryza sativa</i>) has been previously reported, and <i>OsLPR5</i>, functioning in Pi uptake and translocation, is required for the normal growth and development of rice. However, the role of <i>OsLPR3</i>, one of the five members of this family in rice, in response to Pi deficiency and/or in the regulation of plant growth and development is unknown. Therefore, in this study, the roles of <i>OsLPR3</i> in these processes were investigated, and some functions were found to differ between <i>OsLPR3</i> and <i>OsLPR5</i>. <i>OsLPR3</i> was found to be induced in the leaf blades, leaf sheaths, and roots under Pi deprivation. <i>OsLPR3</i> overexpression strongly inhibited the growth and development of the rice but did not affect the Pi homeostasis of the plant. However, <i>oslpr3</i> mutants improved RSA and Pi utilization, and they exhibited a higher tolerance to low Pi stress in rice. The agronomic traits of the <i>oslpr3</i> mutants, such as 1000-grain weight and seed length, were stimulated under Pi-sufficient conditions, indicating that <i>OsLPR3</i> plays roles different from those of <i>OsLPR5</i> during plant growth and development, as well as in the maintenance of the Pi status of rice.