SULTR1;1 high-affinity sulfate transporter is highly regulated by sulfur deficiency (-S) in the epidermis and cortex of Arabidopsis roots. The regulatory mechanism of SULTR1;1 expression was studied using inhibitors for transcription, translation, protein phosphorylation and dephosphorylation. The induction of SULTR1;1 mRNA during -S was blocked by the addition of actinomycin D in the medium, suggesting that SULTR1;1 is transcriptionally regulated. Cycloheximide repressed the -S induction of SULTR1;1, but enhanced the basal mRNA level of SULTR1;1 under sulfur replete (+S) condition. In addition, the induction of SULTR1;1 by -S was significantly blocked by okadaic acid (OKA) and calyculin A (CalyA). Regulation of SULTR1;1 was further confirmed in transgenic plants expressing green fluorescent protein (GFP) under the control of SULTR1;1 promoter. Accumulation of GFP during -S was dependent to SULTR1;1 promoter, and the effects of OKA and CalyA were reproducible in the SULTR1;1 promoter-GFP plants. These results suggested that the up-regulation of SULTR1;1 by -S requires protein phosphatase as an upstream regulatory factor.
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