Ruprecht-Karls-Universität Heidelberg
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Plant Molecular Biology

Prof. Dr. Rüdiger Hell

Regulation of the assimilatory sulfate reduction pathway by internal signals
Fig. 1: Overview of the assimilatory sulfate reduction pathway.
Besides nitrogen (N) and phosphor, sulfur (S) is the most important macronutrient, which is taken up from the soil. The uptake of S as sulfate is mediated via specific transporters and strictly regulated in higher plants to ensure optimal growth. After the uptake of sulfate in the root, sulfate is transported to the shoot, reduced to sulfide and fixed in the proteinogenic amino acid cysteine. The entire reaction cascade including the uptake, activation, reduction and fixation of S is called assimilatory sulfate reduction pathway (ASRP, Fig 1). The strict regulation and coordination of ASRP with diverse metabolic pathways, like carbon (C) and N- fixation, implies the presence of internal signals. The C and N containing precursor of cysteine, O-acetylserine (OAS), is supposed to act as such a signal. The sulfate transporters at the plasmalemma of root cells are known to be induced by high intracellular concentration of OAS, which is dependant of the actual S, C and N supply of the plant (Fig 2). The signal perception and transduction cascade that results in the transcriptional activation of sulfate transporters and key regulators of sulfate reduction are not known at present. A custom made gene array, which covers the complete transcriptome of the ASRP, will be used in combination with N and S-deprivation experiments and knock out mutant of key steps in the ASRP to reveal new targets of regulation by OAS (Fig 3). In addition transgenic plants, which express proteins encoding for key steps in ASRP, will be produced to identify regulatory steps in OAS production and homeostasis.

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