Transcriptional regulation of plant phosphate transporters

Abstract

Phosphorus is acquired by plant roots primarily via the high-affinity inorganic phosphate (P i ) transporters. The transcripts for P i transporters are highly inducible upon P i starvation, which also results in enhanced P i uptake when P i is resupplied. Using antibodies specific to one of the tomato P i transporters (encoded by LePT1), we show that an increase in the LePT1 transcript under P i starvation leads to a concurrent increase in the transporter protein, suggesting a transcriptional regulation for P i acquisition. LePT1 protein accumulates rapidly in tomato roots in response to P i starvation. The level of transporter protein accumulation depends on the P i concentration in the medium, and it is reversible upon resupply of P i . LePT1 protein accumulates all along the roots under P i starvation and is localized primarily in the plasma membranes. These results clearly demonstrate that plants increase their capacity for P i uptake during P i starvation by synthesis of additional transporter molecules.Phosphorus availability is considered one of the major factors that limits growth of plants in natural ecosystems. The concentration of available phosphorus is generally in the micromolar range, which is below that of many micronutrients (1). Consequently plants have developed several adaptive mechanisms to overcome P i deficiency. These include changes in root growth and architecture, increased production of phosphatases and RNases, altered activity of several enzymes of the glycolytic pathway (2, 3), and an increased P i uptake rate of roots (4). The ultimate consequences of these modifications are increased P i availability in the rhizosphere and enhanced uptake.Phosphorus is acquired by the plant roots in an energymediated cotransport process driven by a proton gradient generated by plasma membrane H ϩ -ATPases (5). The kinetic characterization of the P i -uptake system by whole plants and cultured cells indicates a high-affinity transport activity operating at low concentrations (micromolar range) and a lowaffinity activity operating at higher concentrations. The very low concentration (micromolar) of P i in soil solution suggests that high-affinity transporters are primarily involved in P i uptake by plants (3). The low-affinity system is apparently expressed constitutively, whereas the high-affinity system is induced under P i deficiency (6). The induction process appears to involve de novo protein synthesis, since inhibitors of protein synthesis drastically reduce the induction of high-affinity P i transport. The increased synthesis of a high-affinity carrier system has been proposed to be responsible for enhanced P i uptake observed under P i -deficiency conditions (6).High-affinity P i transporter genes have been cloned and characterized from fungi and from several plant species, including Arabidopsis, tomato, potato, Medicago, and Catharanthus (7). All the cloned P i transporters are integral membrane proteins containing 12 membrane-spanning regions, separated into two groups of 6 by a lar...

First evidence on different transportation modes of arsenic and phosphorus in arsenic hyperaccumulator Pteris vittata

“…Published reports indicate that, in response to P deficiency, plants may increase synthesis of additional transporter molecules (Drew et al, 1984) or upregulate expression of genes encoding P transporters (Liu et al, 1998;Muchhal et al, 1996;Smith et al, 1997), leading to a subsequent increase in transporter proteins (Muchhal and Raghothama, 1999). The increase of As(V) uptake with P deficiency has been found by Wang et al (2002), which showed that 8 d of P starvation increases the maximal influx of As(V) by 2.5-fold, suggesting an increased density of P/As(V) transporters in the rhizoid cell plasma membranes.…”

Attenuation of Phosphate Starvation Responses by Phosphite in Arabidopsis

“…These results are in agreement with studies in Brassica sp., which showed that Phi reduced the induction of phosphoenolpyruvate phosphatase, pyrophosphate-dependent phosphofructokinase, and highaffinity Pi uptake in Pi-limiting conditions by 40% to 90% (Carswell et al, 1996(Carswell et al, , 1997. We extended our studies to compare the effect of Pi and Phi on steadystate levels of Pi-responsive mRNAs, which encode a Pi transporter, AtPT2 (Muchhal and Raghothama, 1999), an acid phosphatase, AtACP5 (del Pozo et al, 1999), and an unknown gene product, At4 (Burleigh and Harrison, 1999). Our data clearly indicate that Phi represses Pi starvation-inducible gene expression at the transcript level.…”

“…Although Phi apparently cannot substitute for Pi in terms of meeting the nutritional phosphorus requirements of plants, our data indicate that Phi can substitute for Pi in repressing typical molecular and developmental responses to Pi limitation. Biochemical adaptations to Pi starvation include increased synthesis of anthocyanins, presumably to adjust photosynthetic light reactions to the Pi-dependent Calvin cycle, and increased synthesis of enzymes for scavenging intra-and extracellular phosphorus (Trull et al, 1997;Bosse and Kö ck, 1998;Raghothama, 1999). We previously demonstrated that Pi starvation coordinately induces ribonuclease, phosphodiesterase, and acid phosphatase activities in tomato (Lycopersicon esculentum) cell suspension cultures, which sequentially participate in the complete hydrolysis of exogenous RNA to nucleosides and Pi (Nü rnberger et al, 1990;Abel et al, 2000).…”

“…To cope with low Pi availability, plants have evolved sophisticated developmental and metabolic adaptations to enhance Pi acquisition from the rhizosphere. Such strategies include morphological changes in root architecture and associations with symbiotic mycorrhizal fungi to accelerate soil exploration as well as biochemical responses to chemically increase Pi availability from insoluble salt complexes and organophosphates present in recalcitrant soil matter (McCully, 1999;Raghothama, 1999). Despite numerous studies on adaptive responses to Pi limitation, little is known about the underlying molecular processes or regulatory genes that are involved in the Pi starvation response of plants.…”

“…Inorganic orthophosphate (Pi), the assimilated form of phosphorus, is often a limiting macronutrient in both terrestrial and aquatic ecosystems. As a consequence, assimilation, storage, and metabolism of Pi are highly regulated processes that directly affect plant growth (Theodorou and Plaxton, 1993;Raghothama, 1999). To cope with low Pi availability, plants have evolved sophisticated developmental and metabolic adaptations to enhance Pi acquisition from the rhizosphere.…”