Characterization of the Rice PHO1 Gene Family Reveals a Key Role for OsPHO1;2 in Phosphate Homeostasis and the Evolution of a Distinct Clade in Dicotyledons

Abstract

Phosphate homeostasis was studied in a monocotyledonous model plant through the characterization of the PHO1 gene family in rice (Oryza sativa). Bioinformatics and phylogenetic analysis showed that the rice genome has three PHO1 homologs, which cluster with the Arabidopsis (Arabidopsis thaliana) AtPHO1 and AtPHO1;H1, the only two genes known to be involved in root-toshoot transfer of phosphate. In contrast to the Arabidopsis PHO1 gene family, all three rice PHO1 genes have a cis-natural antisense transcript located at the 5# end of the genes. Strand-specific quantitative reverse transcription-PCR analyses revealed distinct patterns of expression for sense and antisense transcripts for all three genes, both at the level of tissue expression and in response to nutrient stress. The most abundantly expressed gene was OsPHO1;2 in the roots, for both sense and antisense transcripts. However, while the OsPHO1;2 sense transcript was relatively stable under various nutrient deficiencies, the antisense transcript was highly induced by inorganic phosphate (Pi) deficiency. Characterization of Ospho1;1 and Ospho1;2 insertion mutants revealed that only Ospho1;2 mutants had defects in Pi homeostasis, namely strong reduction in Pi transfer from root to shoot, which was accompanied by low-shoot and high-root Pi. Our data identify OsPHO1;2 as playing a key role in the transfer of Pi from roots to shoots in rice, and indicate that this gene could be regulated by its cis-natural antisense transcripts. Furthermore, phylogenetic analysis of PHO1 homologs in monocotyledons and dicotyledons revealed the emergence of a distinct clade of PHO1 genes in dicotyledons, which include members having roles other than long-distance Pi transport.

Spatio-Temporal Transcript Profiling of Rice Roots and Shoots in Response to Phosphate Starvation and Recovery

“…Interestingly, even after 7 d of Pi treatment, the Pi concentration in both root and shoot was still twofold higher than that observed after 21 d of Pi starvation, suggesting that after 7 d of Pi deprivation, plants may not be completely starved (Figures 1F and 1G). The Pi concentration observed after 21 d of Pi starvation in the roots and shoots was similar to that reported in previous long-term Pi starvation studies (Wang et al, 2009a;Secco et al, 2010;Jia et al, 2011;Rouached et al, 2011). In addition, the shoot Pi concentration observed after 21 d of Pi starvation was similar to that of rice shoots when grown in P-poor soils (4.5 mmol/g fresh weight) (H. Shou, unpublished data).…”

A Constitutive Expressed Phosphate Transporter, OsPht1;1, Modulates Phosphate Uptake and Translocation in Phosphate-Replete Rice

“…The PHO1 protein, primarily expressed in the root vascular cylinder, is known for mediating Pi efflux in loading Pi to root xylem in Arabidopsis (Hamburger et al, 2002;Stefanovic et al, 2011). In rice, it has been shown that OsPHO1;2 plays an important role in transferring Pi from roots to shoots (Secco et al, 2010). However, it is not clear if Pht1 members are Figure 9.…”

Phosphate homeostasis in the yeast Saccharomyces cerevisiae, the key role of the SPX domain‐containing proteins

“…In plants, although none of these proteins have yet been characterized as Pi transporters, several proteins possessing the SPX domain have been shown to be major regulators of Pi homeostasis, being involved in Pi signaling, remobilization, export [10,[14][15][16][17][18][19][20]. Moreover, recent work in both yeast and plants report that the SPX domain itself could be involved in fine-tuning of Pi transport and signaling, through mechanisms such as physical interactions with other proteins [12,13,21].…”