Induction of SULTR1;1 sulfate transporter in Arabidopsis roots involves protein phosphorylation/dephosphorylation circuit for transcriptional regulation

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