Cells require sufficient amounts of the element phosphorus to build their membranes and to store and copy genetic information. Phosphorus is taken up by cells in the form of inorganic phosphate, an important signaling molecule and energy currency. While we take up sufficient amounts of phosphate with our diet, plants have to mobilize and take up phosphate from the soil, where it is poorly bioavailable. Phosphate thus limits the growth of plants, and phosphate fertilizers have to be used to maximize crop yields. How plant cells measure cellular phosphate levels and how they decide if and when to take up more phosphate is poorly understood.
The Hothorn lab has previously shown that phosphate-rich inositol pyrophosphates are nutrient messengers in plants and identified SPX domains as their cellular receptors. In a new report, the Hothorn, Hiller (Biozentrum Basel) and Fiedler (FMP Berlin) labs now report that inositol pyrophosphates control the activity of the transcription factor PHOSPHATE STARVATION RESPONSE 1 (PHR1). When there is enough phosphate in the cell, inositol pyrophosphates bind to the SPX receptor which in turn binds to PHR1, keeping it in a isolated form unable to active gene expression. When phosphate becomes limiting, inositol pyrophosphates are less abundant, the SPX – PHR1 complex dissociates and the free transcription factor can interact with itself and activate the expression of genes involved in phosphate uptake. This signaling mechanism may now be exploited towards the development of phosphate starvation tolerant crops that would require less phosphate fertilizer.
The article was published in Nature Communications, on January 15th 2021.