The Arabidopsis SPL9 transcription factor modulates phosphate acquisition and miR399f expression under phosphate deficiency

Abstract Transcription factors have a crucial part in the signaling of Pi deficiency. We report here that the SPL9 of Arabidopsis modulates the phosphate (Pi) deficiency response. To investigate the above, the Pi uptake and content, rhizosphere acidification capacity and anthocyanin content of 35S:rSPL9 (the miR156-resistant form of SPL9) plants were determined. Yeast one-hybrid, transient transfection and ChIP assays were applied to investigate the SPL9 protein binds to the miR399f promoters. The phenotypes of 35S:SPL3 35S:SPL9 lines under Pi deficiency were also determined. The results show that the Pi uptake and content in 35S:rSPL9 plants increased in comparison to the wild-type plants. The decreased rhizosphere acidification capacity and reduced rhizosphere acidification phenotypes in 35S:rSPL9 transgenic plants were observed under the Pi-deficient conditions. The anthocyanin accumulation of 35S:rSPL9 plants was also decreased in response to low Pi stress. The SPL9 protein binds directly to the miR399f promoters at their GTAC motifs. We also found that SPL3 and SPL9 have redundant functions during Pi deficiency responses. These results suggest that SPL9 in Arabidopsis takes part in Pi deficiency response by regulating miR399f expression.