The FvPHR1 transcription factor control phosphate homeostasis by transcriptionally regulating miR399a in woodland strawberry

Plants have evolved phosphate (Pi) starvation response to adapt the low-Pi environment. The regulation of adaptive responses to phosphorus deficiency by the PHR1-miR399-PHO2 module has been well studied in Arabidopsis thaliana but not in strawberry. Transcription factor PHR1 as the central regulator in the Pi starvation signaling has been revealed in a few plant species. However, the function of PHR1 homologues in strawberry is still unknown. In this study, a total of 13 MYB-CC genes were identified in the woodland strawberry (Fragaria vesca) genome and the FvPHR1 gene was characterized. FvPHR1 contains MYB domain and coiled-coil (CC) domain and is localized in the nucleus. FvPHR1 also exhibits trans-activation ability. Furthermore, the P content in leaves of FvPHR1-overexpressing woodland strawberries was significantly increased by 1.38-fold to 1.78-fold compared with that in the wild type. FvPHR1 was also demonstrated to directly bind to the FvMIR399a promoter and positively regulate the expression of FvmiR399a in woodland strawberry. These results showed that PHR1-miR399 module is involved in the regulation of phosphate-signaling pathway and phosphate homeostasis in woodland strawberry.

SPX proteins regulate Pi homeostasis and signaling in different subcellular level

To cope with low phosphate (Pi) availability, plants have to adjust its gene expression profile to facilitate Pi acquisition and remobilization. Sensing the levels of Pi is essential for reprogramming the gene expression profile to adapt to the fluctuating Pi environment. AtPHR1 in Arabidopsis and OsPHR2 in rice are central regulators of Pi signaling, which regulates the expression of phosphate starvation-induced (PSI) genes by binding to the P1BS elements in the promoter of PSI genes. However, how the Pi level affects the central regulator to regulate the PSI genes have puzzled us for a decade. Recent progress in SPX proteins indicated that the SPX proteins play important role in regulating the activity of central regulator AtPHR1/OsPHR2 in a Pi dependent manner at different subcellular levels.