Phosphate signaling in Arabidopsis and Oryza sativa

Phosphate signaling allows unicellular organisms and higher plants to respond and adapt to phosphate starvation efficiently. Four major adaptive processes include root system development, phosphate mobilization, phosphate transport and metabolism. Phosphite, a non-metabolic analog of phosphate, specifically attenuates several phosphate starvation responses, supporting the hypothesis that plants have a phosphate-sensing machinery comparable to that of unicellular organisms. Biochemical and molecular approaches have characterized acid phosphatases, RNases, high-affinity phosphate transporters, and metabolic enzymes as executive proteins in phosphate signaling. Mutant screening in Arabidopsis thaliana have identified several phosphate signaling regulators, such as PHR1, PHO2 and PHF1. PHO2, microRNA399 family and AtIPS1/At4 family represent a novel circuit in phosphate signaling. Microarray studies in A. thaliana and Oryza sativa suggest regulation at the mRNA level can be an important mechanism of phosphate signaling, and that the leaf and the root may occupy two separate phosphate signaling programs. In addition, phosphate signaling is suggested to interact with hormone and sugar signaling pathways. Finally, an integrated model summarizing the contemporary understanding of phosphate signaling, mainly in A. thaliana and O. sativa, is presented.