Inter-organ signaling in plants: regulation of ATP sulfurylase and sulfatetransporter genes expression in roots mediated by phloem-translocated compound

Sulfate uptake and ATP sulfurylase activity in the roots of Arabidopsis tha liana and Brassica napus were enhanced by S deprivation and reduced followi ng resupply of SO42-. Similar responses occurred in split-root experiments where only a portion of the root system was S deprived, suggesting that the regulation involves inter-organ signaling. Phloem-translocated glutathione (GSH) was identified as the likely transducing molecule responsible for re gulating SO42- uptake rate and ATP sulfurylase activity in roots. The regul atory role of GSH was confirmed by the finding that ATP sulfurylase activit y was inhibited by supplying Cys except in the presence of buthionine sulfo ximine, an inhibitor of GSH synthesis. In direct and remote (split-root) ex posures, levels of protein detected by antibodies against the Arabidopsis A PS3 ATP sulfurylase increased in the roots of A. thaliana and B. napus duri ng S starvation, decreased after SO42- restoration, and declined after feed ing GSH. RNA blot analysis revealed that the transcript level of APS1, whic h codes for ATP sulfurylase, was reduced by direct and remote GSH treatment s. The abundance of AST68 (a gene encoding an SO42- transporter) was simila rly affected by altered sulfur status. This report presents the first evide nce for the regulation of root genes involved in nutrient acquisition and a ssimilation by a signal that is translocated from shoot to root.