Molecular Regulation Of Phosphate Starvation-induced Acid Phosphatase Activity

Phosphorus is an essential macronutrient for plant growth and development.However, in most soil, phosphate(Pi), the major form that plants uptake, exist in organic form, which limits plant growth and crop production. To cope with Pi deprivation, plants have evolved diverse adaptive strategies. The induction and secretion of acid phosphatases(APases) is a universal response of plants to phosphate starvation.APases play a vital role in both conservation and remobilization of internal Pi and acquisition Pi from the soil. In Arabidopsis, Pi starvation-mediated induction of root-associated AtPAP10(Arabidopsis Purple Acid Phosphatase 10) activity is tightly regulated at multiple levels; however, the roles of local and systemic signalling involved in this response remain largely unknown.In this work, we show that a decrease in local, external Pi availability is sufficient to induce AtPAP10 transcription in roots; however, the magnitude of the induction is affected by the Pi status in the whole plant. In addition, the triggering of AtPAP10 transcription depends on the presence of sucrose, a systemic signal from shoot. Once the AtPAP10 m RNAs are synthesized in roots, subsequent accumulation of AtPAP10 proteins in root cells and increase of AtPAP10 activity on the root surface are mainly controlled by local signaling. The activity of AtPAP10 on the root surface is further stabilized by external, low Pi levels.Sucrose and ethylene have previously been demonstrated to be positive regulators of root-associated At PAP10 activity. In this study, we provide evidence that, under Pi deficiency, ethylene mainly affects secretion and(or) enzymatic activity of AtPAP10 proteins, but not AtPAP10 transcription and protein accumulation. We also show that the effect of ethylene on the induction of root-associated APase activity depends on sucrose but the effect of sucrose does not depend on ethylene. These results provide insights into the distinct roles of local and systemic signaling in the regulation of plant responses to Pi starvation. In addition, we provide several direct evidences that the AtMYB2-miR399-PHO2 pathway is involved in the control of phosphate starvation-induced APases acitivity, through upregulation of the transcription of several extracellular AtPAP genes.Finally, we characterized an Arabidopsis mutant, hps11(hypersensitive to Pi starvation 11) with enhanced root-associated APases activity. Using map-based cloning approach, we found that hps11 contains a point mutation in a cation exchanger gene.Further functional analysis suggested that proper function of this cation exchanger is important for the secretion of Pi starvation-induced APases.