OsPHF1 Regulates the Plasma Membrane Localization of Low- and High-Affinity Inorganic Phosphate Transporters and Determines Inorganic Phosphate Uptake and Translocation in Rice    

Abstract

PHOSPHATE TRANSPORTER TRAFFIC FACILITATOR1 (PHF1) is known to regulate the plasma membrane localization of PHT1;1, a high-affinity inorganic phosphate (Pi) transporter in Arabidopsis (Arabidopsis thaliana). OsPHF1, a rice (Oryza sativa) gene homologous to AtPHF1, was isolated and found to regulate the localization of both low-and high-affinity Pi transporters to the plasma membrane. Three OsPHF1 allelic mutants carrying one-point mutations at the fifth WD-repeat motif and two at the transmembrane helix, respectively, showed arsenate resistance and severely reduced Pi accumulation. The data indicate that mutation of OsPHF1 results in the endoplasmic reticulum retention of the low-affinity Pi transporter OsPT2 and highaffinity Pi transporter OsPT8. Mutation of OsPHF1 also reduced Pi accumulation in plants exhibiting excessive shoot Pi accumulation due to the overexpression of OsPHR2. However, the transcript level of OsPHF1 itself is not controlled by OsPHR2. Overexpression of OsPHF1 increased Pi accumulation in both roots and shoots in a solution culture with Pi-supplied condition. These results indicate that the role of OsPHF1 is unique in the localization of both low-and high-affinity Pi transporters on the plasma membrane in rice and determines Pi uptake and translocation in rice. The similar function of PHF1 required to facilitate PHT1 transit through the endoplasmic reticulum between Arabidopsis and rice provides an example of expectations from what one would deduce from sequence comparisons to extend knowledge from Arabidopsis to crops.

The Rice CK2 Kinase Regulates Trafficking of Phosphate Transporters in Response to Phosphate Levels

“…Phosphorylation of the PT C-terminal domain by CK2 resulted in ER retention of PT, mimicking the effect of mutations in the ERexit cofactor PHF1 (González et al, 2005;Chen et al, 2011). This suggested that phosphorylation of PT by CK2 might affect its interaction with PHF1.…”

“…As rice CK2a3/b3 could phosphorylate the homologous serine site in PT8 (Figures 2A and 2C; Chen et al, 2011), this CK2 could function to modulate the ER exit of PTs. To test this possibility, we examined the subcellular localizations of GFP-tagged PT2/OsPT8.…”

“…Accordingly, we tested for interactions of a-subunits with the PTs in the presence of CK2b3. The hydrophilic C termini (CT) of PT2/PT8, including the putative phosphorylation sites ( Figure 1C; Bayle et al, 2011;Chen et al, 2011), were used in a yeast three-hybrid assay with two different CK2a (a2/a3) catalytic subunits in the presence or absence of CK2b3. CK2b3 was found to be necessary for the interaction between CK2a3 and PT2/PT8-CT in these assays ( Figure 1D), suggesting that CK2a3, CK2b3, and the C termini of PT2/PT8 form a complex in yeast.…”

“…PHOSPHATE TRANSPORTER TRAFFIC FACILITATOR1 (PHF1) plays a major role in regulating the trafficking of PTs from the endoplasmic reticulum (ER) to the PM (González et al, 2005;Chen et al, 2011). In addition, posttranslational control of PHT1 family members at the level of protein stability involves both PHOSPHATE2 (PHO2) and NITROGEN LIMITATION ADAPTATION (NLA), two components of the ubiquitin-mediated degradation pathway Lin et al, 2013;Park et al, 2014).…”

Complementary Proteome and Transcriptome Profiling in Phosphate-deficient Arabidopsis Roots Reveals Multiple Levels of Gene Regulation

“…A third subcluster contains several RNA-binding proteins, some of which have been attributed to RNA processing or to the regulation of meiosis. This cluster also contains the PHOS-PHATE TRANSPORTER TRAFFIC FACILITATOR 1 (PHF1), which is required for the transport of high-affinity phosphate transporters from the ER to the plasma membrane in Arabidopsis and rice (36,37). Interestingly, PHF1 is connected to the network by a single edge via the binding partner of the target of rapamycin (TOR) kinase RAPTOR1B.…”