Two distinct high-affinity sulfate transporters with different inducibilities mediate uptake of sulfate in Arabidopsis roots.
Sulfate transporters present at the root surface facilitate uptake of sulfate from the environment. Here we report that uptake of sulfate at the outermost cell layers of Arabidopsis root is associated with the functions of highly and low-inducible sulfate transporters, Sultr1;1 and Sultr1;2, respectively. We have previously reported that Sultr1;1 is a high-affinity sulfate transporter expressed in root hairs, epidermal and cortical cells of Arabidopsis roots, and its expression is strongly upregulated in plants deprived of external sulfate. A novel sulfate transporter gene, Sultr1;2, identified on the BAC clone F28K19 of Arabidopsis, encoded a polypeptide of 653 amino acids that is 72.6% identical to Sultr1;1 and was able to restore sulfate uptake capacity of a yeast mutant lacking sulfate transporter genes (K(m) for sulfate = 6.9 +/- 1.0 microm). Transgenic Arabidopsis plants expressing the fusion gene construct of the Sultr1;2 promoter and green fluorescent protein (GFP) showed specific localization of GFP in the root hairs, epidermal and cortical cells of roots, and in the guard cells of leaves, suggesting that Sultr1;2 may co-localize with Sultr1;1 in the same cell layers at the root surface. Sultr1;1 mRNA was abundantly expressed under low-sulfur conditions (50-100 microm sulfate), whereas Sultr1;2 mRNA accumulated constitutively at high levels under a wide range of sulfur conditions (50-1500 microm sulfate), indicating that Sultr1;2 is less responsive to changes in sulfur conditions. Addition of selenate to the medium increased the level of Sultr1;1 mRNA in parallel with a decrease in the internal sulfate pool in roots. The level of Sultr1;2 mRNA was not influenced under these conditions. Antisense plants of Sultr1;1 showed reduced accumulation of sulfate in roots, particularly in plants treated with selenate, suggesting that the inducible transporter Sultr1;1 contributes to the uptake of sulfate under stressed conditions.
Yoshimoto
Naoko
N
Department of Molecular Biology and Biotechnology, Graduate School of Pharmaceutical Sciences, Chiba University, Yayoi-cho 1-33, Inage-ku, Chiba 263-8522, Japan.
Takahashi
Hideki
H
Smith
Frank W
FW
Yamaya
Tomoyuki
T
Saito
Kazuki
K
D000595:Amino Acid Sequence; D027321:Anion Transport Proteins; D017360:Arabidopsis / Q000235:genetics* / Q000502:physiology; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000502:physiology; D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D018506:Gene Expression Regulation, Plant / Q000235:genetics; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D019441:Plant Epidermis / Q000235:genetics / Q000502:physiology; D018515:Plant Leaves / Q000235:genetics / Q000502:physiology; D018517:Plant Roots / Q000235:genetics* / Q000502:physiology; D030821:Plants, Genetically Modified; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D064586:Selenic Acid; D018036:Selenium Compounds / Q000494:pharmacology; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D000076988:Sulfate Transporters; D013431:Sulfates / Q000378:metabolism* / Q000494:pharmacology; D013455:Sulfur / Q000172:deficiency / Q000378:metabolism
D027321:Anion Transport Proteins; D029681:Arabidopsis Proteins; D002352:Carrier Proteins; D018076:DNA, Complementary; D008164:Luminescent Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D012333:RNA, Messenger; C085609:SLC26A4 protein, human; D018036:Selenium Compounds; D000076988:Sulfate Transporters; D013431:Sulfates; C455459:Sultr1;1 protein, Arabidopsis; C455460:Sultr1;2 protein, Arabidopsis; D049452:Green Fluorescent Proteins; D013455:Sulfur; D064586:Selenic Acid