Summary • Plants have developed several methods of adapting to conditions of low phosphorus (P). However, details of the regulation of the gene expression system that responds to P status of plants is unknown. Here, a phosphorus limitation inducible novel gene was isolated and characterized to provide further information of plant adaptation to low P. • Rice plants (Oryza sativa) were grown hydroponically with or without P. A novel gene was isolated by cDNA microarray analysis and designated as OsPI1 ( Oryza sativa Phosphate-limitation Inducible Gene 1). mRNA accumulation was examined by Northern blot and quantitative real time PCR. • The OsPI1 gene was rapidly induced by phosphate starvation in both shoots and roots. When phosphate was supplied to phosphate-deficient plants, the OsPI1 transcripts rapidly disappeared. OsPI1 cDNA consisted of 375 bp and contained several small open reading frames (ORFs). The OsPI1 gene shows the same characteristics as the TPSI1/Mt4 family (the phosphate starvation inducible novel gene family). • It is suggested that OsPI1 acts as riboregulator, that is, it binds with other molecules under phosphate starvation and regulates their function.