Selenate‐resistant mutants of Arabidopsis thaliana identify Sultr1;2, a sulfate transporter required for efficient transport of sulfate into roots

Abstract

SummaryTo investigate how plants acquire and assimilate sulfur from their environment, we isolated and characterized two mutants of Arabidopsis thaliana de®cient in sulfate transport. The mutants are resistant to selenate, a toxic analogue of sulfate. They are allelic to each other and to the previously isolated sel1 (selenate-resistant) mutants, and have been designated sel1-8 and sel1-9. Root elongation in these mutants is less sensitive to selenate than in wild-type plants. Sulfate uptake into the roots is impaired in the mutants under both sulfur-suf®cient and sulfur-de®cient conditions, but transport of sulfate to the shoot is not affected. The sel1 mutants contain lesions in the sulfate transporter gene Sultr1;2 located on the lower arm of chromosome 1. The sel1-1, sel1-3 and sel1-8 mutants contain point mutations in the coding sequences of Sultr1;2, while the sel1-9 mutant has a T-DNA insertion in the Sultr1;2 promoter. The Sultr1;2 cDNA derived from wild-type plants is able to complement Saccharomyces cerevisiae mutants defective in sulfate transport, but the Sultr1;2 cDNA from sel1-8 is not. The Sultr1;2 gene is expressed mainly in roots, and accumulation of transcripts increases during sulfate deprivation. Examination of transgenic plants containing the Sultr1;2 promoter fused to the GUS-reporter gene indicates that Sultr1;2 is expressed mainly in the root cortex, the root tip and lateral roots. Weaker expression of the reporter gene was observed in hydathodes, guard cells and auxiliary buds of leaves, and in anthers and the basal parts of¯owers. The results indicate that Sultr1;2 is primarily involved in importing sulfate from the environment into the root.

Isolation and Characterization of an Arabidopsis Mutant That Overaccumulates O-Acetyl-l-Ser

“…We showed that the expression of endogenous S-responsive genes was also up-regulated in osh1-1. During the course of this study, a mutant having a lesion in the sulfate transporter 1;2 gene (Shibagaki et al, 2002;Yoshimoto et al, 2002) was also isolated (N. Ohkama-Ohtsu, Y. Ide, and T. Fujiwara, unpublished data), which supports the validity of our screening strategy. To our (Arunachalam et al, 2000) are italicized and underlined, respectively.…”

Phloem-Localizing Sulfate Transporter, Sultr1;3, Mediates Re-Distribution of Sulfur from Source to Sink Organs in Arabidopsis

“…We have recently characterized the function of two distinct high-affinity sulfate transporters, Sultr1;1 and Sultr1;2, that facilitate the initial uptake of sulfate at the root epidermis and cortex in Arabidopsis (Shibagaki et al, 2002;Yoshimoto et al, 2002). In the present study, a putative open reading frame, At1g22150, that potentially encodes the third isoform of the high-affinity sulfate transporter in Arabidopsis was identified on the BAC clone F2E2 (accession no.…”

“…In the past few years, numbers of genes encoding high-affinity sulfate transporters in vascular plants have been isolated and characterized (Smith et al, 1995(Smith et al, , 1997Vidmar et al, 1999;Takahashi et al, 2000;Shibagaki et al, 2002;Yoshimoto et al, 2002). These high-affinity sulfate transporters are predominantly expressed in roots of sulfur-starved plants and are suggested to serve for the initial uptake of sulfate from the soil.…”

“…These high-affinity sulfate transporters are predominantly expressed in roots of sulfur-starved plants and are suggested to serve for the initial uptake of sulfate from the soil. The Arabidopsis Sultr1;1 and Sultr1;2 localize at the epidermis and cortex of roots, and are highly regulated by sulfur nutrition (Takahashi et al, 2000;Shibagaki et al, 2002;Yoshimoto et al, 2002). Direct contribution of Sultr1;1 or Sultr1;2 to the uptake of sulfate in root was elucidated in the knockout mutant and antisense plants in Arabidopsis (Shibagaki et al, 2002;Yoshimoto et al, 2002).…”

“…The Arabidopsis Sultr1;1 and Sultr1;2 localize at the epidermis and cortex of roots, and are highly regulated by sulfur nutrition (Takahashi et al, 2000;Shibagaki et al, 2002;Yoshimoto et al, 2002). Direct contribution of Sultr1;1 or Sultr1;2 to the uptake of sulfate in root was elucidated in the knockout mutant and antisense plants in Arabidopsis (Shibagaki et al, 2002;Yoshimoto et al, 2002). In the present study, the third isoform of the high-affinity sulfate transporter, Sultr1;3, was identified in Arabidopsis and was demonstrated to show specific function for the loading of sulfate into the sieve tube, facilitating retranslocation of sulfur source in plants.…”