PHOSPHATE TRANSPORTER TRAFFIC FACILITATOR1 Is a Plant-Specific SEC12-Related Protein That Enables the Endoplasmic Reticulum Exit of a High-Affinity Phosphate Transporter in Arabidopsis  [W]

Abstract

PHOSPHATE TRANSPORTER1 (PHT1) genes encode phosphate (Pi) transporters that play a fundamental role in Pi acquisition and remobilization in plants. Mutation of the Arabidopsis thaliana PHOSPHATE TRANSPORTER TRAFFIC FACILITA-TOR1 (PHF1) impairs Pi transport, resulting in the constitutive expression of many Pi starvation-induced genes, increased arsenate resistance, and reduced Pi accumulation. PHF1 expression was detected in all tissues, particularly in roots, flowers, and senescing leaves, and was induced by Pi starvation, thus mimicking the expression patterns of the whole PHT1 gene family. PHF1 was localized in endoplasmic reticulum (ER), and mutation of PHF1 resulted in ER retention and reduced accumulation of the plasma membrane PHT1;1 transporter. By contrast, the PIP2A plasma membrane protein was not mislocalized, and the secretion of Pi starvation-induced RNases was not affected in the mutant. PHF1 encodes a plantspecific protein structurally related to the SEC12 proteins of the early secretory pathway. However, PHF1 lacks most of the conserved residues in SEC12 proteins essential as guanine nucleotide exchange factors. Although it functions in early secretory trafficking, PHF1 likely evolved a novel mechanism accompanying functional specialization on Pi transporters. The identification of PHF1 reveals that plants are also endowed with accessory proteins specific for selected plasma membrane proteins, allowing their exit from the ER, and that these ER exit cofactors may have a phylum-specific origin.

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.…”

“…One PCR product (597 bp) was obtained from Osphf1-1 and two PCR products (597 and 216 bp) were obtained from the complementation lines. The primers are listed in Supplemental Table S1 It has been suggested that AtPHF1 may be regulated by AtPHR1 (At3g52190; Gonzalez et al, 2005). To determine whether OsPHF1 is regulated by OsPHR2, a functional rice homolog of AtPHR1 (Zhou et al, 2008), plants overexpressing OsPHR2 in a phf1-1 background (designated as phf1-1;OvPHR2) were developed by crossing the phf1-1 mutant with transgenic plants overexpressing OsPHR2 (Zhou et al, 2008).…”

“…This step is mediated by COPII vesicles (Barlowe and Schekman, 1993;Barlowe, 2003). In Arabidopsis, the PHOSPHATE TRANSPORTER TRAFFIC FACILITATOR1 (PHF1) is reported to be an important factor for the localization of high-affinity Pi transporters to the plasma membrane (Gonzalez et al, 2005). Mutation of AtPHF1 specifically impairs Pi transport and results in the constitutive expression of many Pi starvation-induced genes, increased arsenate (As) resistance, and reduced Pi accumulation.…”

The Phosphate Fast-Responsive Genes PECP1 and PPsPase1 Affect Phosphocholine and Phosphoethanolamine Content

“…The fugu5-1 through -3 mutants as well as fugu5-1 PromAVP1:IPP1 #8-3 were previously described (Ferjani et al, 2011). The phr1 phl1 double mutant was also previously described (González et al, 2005;Bustos et al, 2010) …”

Arabidopsis BTB/POZ protein-dependent PENETRATION3 trafficking and disease susceptibility

“…Our findings pave the way for identification of cytosolic EAP3 interactors and for characterising the precise functions of the EAP3 protein domains during PEN3 exit from the ER. Interestingly, the ER accessory protein AUXIN RESISTANT4 and the PHOSPHATE TRANSPORTER TRAFFIC FACILITATOR1 protein, both unrelated to EAP3, mediate trafficking of specific cargos from the ER 19,20 , although the underlying molecular mechanisms remain unknown. These examples highlight future opportunities in studying molecular mechanisms underlying ER exit of specific cargos involved in important physiological processes such as hormone or phosphate transport, and disease resistance in plants, to understand the physiological relevance of such specificity.…”