Poster: Nutrient Biology

Abs # 406: Regulatory roles of plasma membrane and vacuolar sulfate transporters for the uptake and root-to-shoot translocation of sulfate in Arabidopsis

Presenter:	Takahashi, Hideki , hideki@postman.riken.go.jp
Authors	Takahashi, Hideki  (A)   Watanabe-Takahashi, Akiko  (A)   Yoshimoto, Naoko  (A) (B)  Kataoka, Tatsuhiko  (A)   Saito, Kazuki  (B)   Yamaya, Tomoyuki  (A) (C)
Affiliations:	(A): RIKEN Plant Science Center (B): Chiba University (C): Tohoku University

Here we report the in planta roles of four distinct isoforms of sulfate transporters that regulate uptake and internal translocation of sulfate in Arabidopsis. Sultr1;1 and Sultr1;2 encode high-affinity transporters responsible for the initial uptake of sulfate in the epidermis, cortex and root hairs of Arabidopsis root. The sultr1;2 T-DNA insertion mutant showed substantial accumulation of Sultr1;1 mRNA, however this compensatory regulation was not able to restore the sulfate uptake. The mutant showed general symptoms of sulfur deficiency as indicated by activation of sulfur assimilation and induction of oxidative stress response. The growth of sultr1;1 sultr1;2 double mutant was significantly impaired particularly under sulfur limited conditions. The result indicated that both Sultr1;1 and Sultr1;2 are the components of the initial high-affinity sulfate uptake system in Arabidopsis roots. Sulfate transporters encoded by Sultr4;1 and Sultr4;2 are localized in the tonoplast membranes. Both transporters were abundantly expressed in the pericycle and xylem parenchyma cells. Disruption of Sultr4;1 and Sultr4;2 by T-DNA insertion caused increased accumulation of sulfate and decrease of glutathione contents. During sulfur starvation, the sulfate pool of sultr4;1 sultr4;2 double mutant was retained at higher levels than in the wild type plants, suggesting that Sultr4;1 and Sultr4;2 are facilitating the efflux of sulfate from vacuole to cytoplasm. The sultr4;1 sultr4;2 double mutant showed substantial increase of sulfate uptake. Additionally, the rate of root-to-shoot transport of sulfate was significantly restricted in this mutant, suggesting that release of sulfate to the xylem is controlled by efflux of sulfate from the vacuole.