The Rice Protein Kinase PSTOL1 Enhances Root Growth As a Mechanism For Phosphorus Deficiency Tolerance

Phosphorus (P)-fertilizer is derived from non-renewable and diminishing phosphate rock reserves. Applied fertilizer supports plant growth, however, P may be fixed and not easily available to the plants. More than a decade ago, Phosphorus uptake 1 (Pup1), a major rice quantitative locus (QTL) for P-deficiency tolerance, was identified. The Pup1 locus, which is derived from the aus-type rice variety Kasalath, was not associated with known P uptake-related mechanisms suggesting a new tolerance mechanism or the involvement of a gene absent from the Nipponbare reference genome. It has now been shown that the Pup1 region indeed contains a Kasalath-specific gene, PHOSPHORUS STARVATION TOLERANCE 1 (PSTOL1), which encodes a Ser/Thr protein kinase. Overexpression of the PSTOL1 gene in two intolerant rice varieties that inherently lack this gene enhanced grain yield and root growth in P-deficient soil. OsPSTOL1 is expressed in root primordia and acts as an enhancer of root growth. We conclude that PSTOL1 confers tolerance of P deficiency by enhancing root growth which provides plants with an advantage in the access to P and other soil nutrients. Gene-specific markers have been developed to facilitate introgression of the Pup1 QTL into local rice varieties to improve productivity in areas with low soil P conditions. This study also highlights the importance of traditional rice varieties as donors of high value genes such as OsPSTOL1 or the submergence-tolerance gene SUB1A, which is likewise absent from modern rice varieties, in supporting food security especially for poor farmers who are often growing rice in stress-prone environments.