Arabidopsis thaliana High-Affinity Phosphate Transporters Exhibit Multiple Levels of Posttranslational Regulation  

Abstract

In Arabidopsis thaliana, the PHOSPHATE TRANSPORTER1 (PHT1) family encodes the high-affinity phosphate transporters. They are transcriptionally induced by phosphate starvation and require PHOSPHATE TRANSPORTER TRAFFIC FACILITATOR (PHF1) to exit the endoplasmic reticulum (ER), indicating intracellular traffic as an additional level of regulation of PHT1 activity. Our study revealed that PHF1 acts on PHT1, upstream of vesicle coat protein COPII formation, and that additional regulatory events occur during PHT1 trafficking and determine its ER exit and plasma membrane stability. Phosphoproteomic and mutagenesis analyses revealed modulation of PHT1;1 ER export by Ser-514 phosphorylation status. Confocal microscopy analysis of root tip cells showed that PHT1;1 is localized to the plasma membrane and is present in intracellular endocytic compartments. More precisely, PHT1;1 was localized to sorting endosomes associated with prevacuolar compartments. Kinetic analysis of PHT1;1 stability and targeting suggested a modulation of PHT1 internalization from the plasma membrane to the endosomes, followed by either subsequent recycling (in low Pi) or vacuolar degradation (in high Pi). For the latter condition, we identified a rapid mechanism that reduces the pool of PHT1 proteins present at the plasma membrane. This mechanism is regulated by the Pi concentration in the medium and appears to be independent of degradation mechanisms potentially regulated by the PHO2 ubiquitin conjugase. We propose a model for differential trafficking of PHT1 to the plasma membrane or vacuole as a function of phosphate concentration.

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

“…5, A and B). The ER location of PHF1 has been confirmed in Arabidopsis (Gonzalez et al, 2005;Bayle et al, 2011). Our data showed that OsPHF1 is also located in ER (Fig.…”

“…Recently, PHF1 as a PHT1-specific facilitator required for PHT1 transiting through the ER to plasma membrane has been demonstrated. In the posttranslational regulation of PHT1, phosphorylation of PHT1 modulates ER exit and targeting to the plasma membrane that is conserved in PHT1 (Bayle et al, 2011). Additional evidence to the function of PHF1 in regulation of Pi uptake has been reported from its function involved in the excessive leaf Pi accumulation in nitrogen limitation adaptation (nla) mutant at low-NO 3 2 supply (Kant et al, 2011).…”

“…In Arabidopsis, mutations in PHF1 lead to increased As resistance and reduced Pi accumulation (Gonzalez et al, 2005). Recently a model for differential trafficking of PHT1 to the plasma membrane or vacuole as a function of phosphate concentration has been proposed where PHF1 acts on PHT1, upstream of vesicle coat protein COPII formation (Bayle et al, 2011). Hence, the investigation of PHF1 function in rice may provide information useful for the development of crops with enhanced Pi efficiency.…”

Development of real-time radioisotope imaging systems for plant nutrient uptake studies

“…Nevertheless, the resolutions in these experiments were far from that obtained here, where it was possible to clearly visualize the labelling of the meristem area, distinct from the uptake at the level of root hairs above the area of differentiation. This clearly illustrates the importance of the role of the PHT1 family of phosphate transporters, which have recently been shown to be strongly expressed in the root cap of Arabidopsis [18].…”

ESCRT-I Component VPS23A Affects ABA Signaling by Recognizing ABA Receptors for Endosomal Degradation

“…Known targets of the endocytic trafficking route in plants include the auxin carriers PIN1, PIN2, and AUX1, the iron transporter IRT1, the boric acid/borate exporter BOR1, the flagellin receptor FLS2, the brassinosteroid receptor BRI1, and the high-affinity phosphate transporter PHT1 (Barberon et al, 2011;Bayle et al, 2011;Geldner et al, 2001;Kasai et al, 2011;Kleine-Vehn et al, 2006;Kleine-Vehn et al, 2008;Spallek et al, 2013;Spitzer, et al, 2009). (Slagsvold et al, 2006).…”