Overexpression of an Arabidopsis thaliana high-affinity phosphate transporter gene in tobacco cultured cells enhances cell growth under phosphate-limited conditions

Abstract

A higher plant homologue to the highaffinity phosphate transporter gene of yeast (Saccharomyces cerevisiae) PHO84 was isolated from Arabidopsis thaliana. Expression of the Arabidopsis gene PHT1 at high levels in tobacco-cultured cells increased the rate of phosphate uptake. The uptake activity attributable to the transgene was inhibited by protonophores, suggesting an H ؉ cotransport mechanism of phosphate uptake, and had a K m of 3.1 M which is within limits characteristic of high-affinity transport mechanisms. These results indicate that PHT1 encodes a high-affinity phosphate transporter. The transgenic cells exhibited increased biomass production when the supply of phosphate was limited, establishing gene engineering of phosphate transport as one approach toward enhancing plant cell growth.

Closely Related Members of the Medicago truncatula PHT1 Phosphate Transporter Gene Family Encode Phosphate Transporters with Distinct Biochemical Activities

“…As shown by the data presented here, M. truncatula has at least one P i transporter, MtPT5, that shows a high affinity for P i when expressed in yeast. The apparent K m of 13 M is similar to that of the PHO84 transporter of yeast, which shows a K m for P i of 8 M, and to K m values of P i transporters from Arabidopsis and barley as assessed in plant cell cultures (24,28). In contrast, the MtPT1, MtPT2, and MtPT3 transporters show a moderate to low affinity for P i with apparent K m values in the 500 -800 M range.…”

“…Overlapping expression patterns have been reported for the PHT1 P i transporters in other plant species also (14,19,20,(22)(23)(24)(25)(26). The biochemical activities of only a few PHT1 P i transporters have been analyzed, either by expression in yeast P i transport mutants, or in plant cells (11,13,15,24,27,28). The transporters show a range of affinities for P i with apparent K m values between 9 and 668 M. In Arabidopsis two P i transporters, Pht1;1 and Pht1;4, mediate 75% of the P i uptake capacity of the roots system and consistent with their expression patterns, they appear to function in a wide range of P i environments (29).…”

Identification and Characterization of the Arabidopsis PHO1 Gene Involved in Phosphate Loading to the Xylem

“…The AtPT1 gene from Arabidopsis was the first high-affinity H ϩ -Pi cotransporter identified in higher plants (Muchhal et al, 1996). At least nine genes showing similarity to AtPT1 have been identified in Arabidopsis from expressed sequence tags and genome sequence analysis, although the expression of only AtPT1 and AtPT2 are readily detectable by RNA gel blot analysis (Muchhal et al, 1996;Lu et al, 1997;Mitsukawa et al, 1997;Smith et al, 1997;Okumura et al, 1998;Raghothama, 2000). Homologs of AtPT1 also have been identified in Catharanthus roseus ( CrPT1 ; Kai et al, 1997), potato ( StPT1 and StPT2 ; Leggewie et al, 1997), tomato ( LePT1 and LePT2 ; Daram et al, 1998;Liu et al, 1998a), Medicago trunculata ( MtPT1 and MtPT2 ; Liu et al, 1998b), tobacco ( NtPT1 ), and wheat ( TaPT1 ) (Raghothama, 2000).…”

Promoter Analysis of the Barley Pht1;1 Phosphate Transporter Gene Identifies Regions Controlling Root Expression and Responsiveness to Phosphate Deprivation

“…Pi transporters belonging to two major gene families (Pht1 and Pht2) have now been identified for a range of plant species (for review, see Rausch and Bucher, 2002) and have been most extensively studied in Arabidopsis (Arabidopsis thaliana; Muchhal et al, 1996;Mitsukawa et al, 1997;Smith et al, 1997Smith et al, , 2000Okumura et al, 1998;Karthikeyan et al, 2002;Mudge et al, 2002). The members of the gene family that are expressed in roots are typically up-regulated under P deficiency, but the molecular basis of the regulation has not been investigated.…”