Modulation of Shoot Phosphate Level and Growth byPHOSPHATE1Upstream Open Reading Frame1[OPEN]

An upstream open reading frame in the 5MODIFIER LETTER PRIME untranslated region of a phosphate transporter gene inhibits its translation in a phosphate-independent manner, and this regulation can be harnessed to increase shoot phosphate accumulation and improve growth under phosphate deficiency. Inorganic orthophosphate (Pi) is an essential nutrient for plant growth, and its availability strongly impacts crop yield. PHOSPHATE1 (PHO1) transfers Pi from root to shoot via Pi export into root xylem vessels. In this work, we demonstrate that an upstream open reading frame (uORF) present in the 5 ' untranslated region of the Arabidopsis (Arabidopsis thaliana)PHO1inhibits its translation and influences Pi homeostasis. The presence of the uORF strongly inhibited the translation of aPHO15 ' UTR-luciferase construct in protoplasts. A point mutation removing thePHO1uORF (Delta uORF) in transgenic Arabidopsis resulted in increased association of its mRNA with polysomes and led to higher PHO1 protein levels, independent of Pi availability. Interestingly, deletion of the uORF led to higher shoot Pi content and was associated with improved shoot growth under low external Pi supply and no deleterious effects under Pi-sufficient conditions. We further show that natural accessions lacking thePHO1uORF exhibit higher PHO1 protein levels and shoot Pi content. Increased shoot Pi content was linked to the absence of thePHO1uORF in a population of F2 segregants. We identified thePHO1uORF in genomes of crops such as rice (Oryza sativa), maize (Zea mays), barley (Hordeum vulgare), and wheat (Triticum aesativum), and we verified the inhibitory effect of the ricePHO1uORF on translation in protoplasts. Our work suggests that regulation of PHO1 expression via its uORF might be a genetic resource useful-both in natural populations and in the context of genome editing-toward improving plant growth under Pi-deficient conditions.