Alkaline phosphatase-coupled high affinity phosphate transporters were involved in low phosphorus stress responding in Pyropia yezoensis

Phosphate (Pi) often becomes a limiting nutrient in oceans, particularly in macroalgae aquaculture areas. More importantly, the continuous increase of Pyropia yezoensis cultivation density has exacerbated Pi deficiency issues. This study used transcriptome analysis of Py. yezoensis seedlings under low-Pi conditions and identified the gene PyALP, an alkaline phosphatase, which was significantly upregulated. Through Weighted Gene Co-expression Network Analysis (WGCNA) and Pearson correlation, PyPHO89, a Pi transporter gene, and six transcription factors were co-expressed with PyALP. Bioinformatics predictions indicated that PyALP belongs to a PhoA type enzyme. However, the molecular structures of the glycosylphosphatidylinositol (GPI) and anchor the N-terminal glycine were not detected, suggesting that PyALP is confined to the microenvironment between the cell wall and plasma membrane, where it hydrolyzes dissolved organic phosphorus (DOP). PyPHO89 was predicted to be a high-affinity symporter for inorganic phosphorus uptake. Promoter analysis revealed Myb binding sites in both PyALP and PyPHO89. Among the screened potential transcription factor genes, only Py08914 possessed a conserved SHLQKYR motif and a glutamine-rich C-terminal sequence, which are characteristic of a typical Pi deficiency-responsive transcription factor. Quantitative RT-PCR showed upregulation of PyALP and PyPHO89 after 6 h of Pi-starvation, and expression of Py08914 peaked in the first 2–4 h of starvation. This implies that the hydrolysis of DOP and uptake of phosphorus are co-regulated by the Myb transcription factor. PyALP activity increased with Pi-starvation and both phosphoesters and phosphonates could be used with similar efficiency. This is the first report regarding the Pi-deficiency response mechanism in Py. yezoensis.