Two cDNAs from Potato Are Able to Complement a Phosphate Uptake-Deficient Yeast Mutant: Identification of Phosphate Transporters from Higher Plants

Abstract

Acquisition as well as translocation of phosphate are essential processes for plant growth. In many plants, phosphate uptake by roots and distribution within the plant are presumed to occur via a phosphate/proton cotransport mechanism. Here, we describe the isolation of two cDNAs, StPT1 and StPT2, from potato (Solanum tuberosum) that show homology to the phosphate/proton cotransporter PHO84 from the yeast Saccharomyces cerevisiae. The predicted products of both cDNAs share 35% identity with the PHO84 sequence. The deduced structure of the encoded proteins revealed 12 membrane-spanning domains with a central hydrophilic region. The molecular mass was calculated to be 59 kD for the StPT1 protein and 58 kD for the StPT2 protein. When expressed in a PHO84-deficient yeast strain, MB192, both cDNAs complemented the mutant. Uptake of radioactive orthophosphate by the yeast mutant expressing either StPT1 or StPT2 was dependent on pH and reduced in the presence of uncouplers of oxidative phosphorylation, such as 2,4-dinitrophenol or carbonyl cyanide m-chlorophenylhydrazone. The K(m) for Pi uptake of the StPT1 and StPT2 proteins was determined to be 280 and 130 microM, respectively. StPT1 is expressed in roots, tubers, and source leaves as well as in floral organs. Deprivation of nitrogen, phosphorus, potassium, and sulfur changed spatial expression as well as the expression level of StPT1. StPT2 expression was detected mainly in root organs when plants were deprived of Pi and to a lesser extent under sulfur deprivation conditions. No expression was found under optimized nutrition conditions or when other macronutrients were lacking.

The spatial expression patterns of a phosphate transporter (MtPT1) from Medicago truncatula indicate a role in phosphate transport at the root/soil interface

“…We have shown previously that MtPT1 is regulated in response to the phosphate status of the plant, as are the phosphate transporter genes from Arabidopsis (AtPT1, AtPT2) (Muchhal et al, 1996;, tomato (LePT1, LePT2) (Liu et al, 1998a) and potato (StPT1, StPT2) (Leggewie et al, 1997). Here, Western blot analysis demonstrates that the MtPT1 protein levels correlate with the MtPT1 transcript levels and are highest in plants grown under phosphate limiting conditions and are almost undetectable in those grown in high phosphate conditions.…”

“…This includes transporters from potato (StPT1 and StPT2) (Leggewie et al, 1997), Arabidopsis thaliana (AtPT1 and AtPT2) (Muchhal et al, 1996;, Medicago truncatula (MtPT1 and MtPT2) (Liu et al, 1998b) and tomato (LePT1 and LePT2) (Daram et al, 1998;Liu et al, 1998a). The encoded proteins share between 75 and 85% identity at the amino acid level and are distinct from PHT2;1.…”

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]

“…To gain insights into the functional implications of these differences between PHF1 and SEC12, we examined whether Arabidopsis PHF1 could functionally replace SEC12 in yeast. To this end, we cloned Arabidopsis PHF1 and SEC12 (STL2P) open reading frames in p181A1NE (Leggewie et al, 1997) under the control of the constitutive ADH promoter and transformed a temperature-sensitive sec12 mutant of yeast. In accordance with previous reports (d 'Enfert et al, 1992), Arabidopsis SEC12 (STL2P) could rescue the growth defect of the mutant yeast at 378C; however, PHF1 could not ( Figure 3E).…”

“…Complementation tests in yeasts were performed using PHF1 and STL2P open reading frames (d 'Enfert et al, 1992) cloned into p181A1NE (Leggewie et al, 1997). Transformation of the resulting constructs into the Saccharomyces cerevisiae sec12 mutant (RSY653; d 'Enfert et al, 1991) was made according to Gietz and Woods (2002).…”

Reproductive biomass in Holcus lanatus clones that differ in their phosphate uptake kinetics and mycorrhizal colonization

“…HAUS is dominant when substrate concentrations are below 0n1 mol m −$ *Author for correspondence (tel j44 1904 432814 ; fax j44 1904 434 385 ; e-mail wjw100!york.ac.uk). (Clarkson & Lu$ ttge, 1991) and has carrier-mediated transport (Leggewie et al, 1997 ;Maathuis & Sanders, 1993 ;Smith et al, 1997).…”