Sulfate is transported at significant rates through the symbiosome membrane and is crucial for nitrogenase biosynthesis

Sebastian Schneider, Arno Schintlmeister, Manuel Becana, Michael Wagner, Dagmar Woebken, Stefanie Wienkoop

Legume-rhizobia symbioses play a major role in food production for an ever growing human population. In this symbiosis, dinitrogen is reduced ('fixed') to ammonia by the rhizobial nitrogenase enzyme complex and is secreted to the plant host cells, while dicarboxylic acids derived from photosynthetically-produced sucrose are transported into the symbiosomes and serve as respiratory substrates for the bacteroids. The symbiosome membrane contains high levels of SST1 protein, a sulfate transporter. Sulfate is an essential nutrient for all living organisms, but its importance for symbiotic nitrogen fixation and nodule metabolism has long been underestimated. Using chemical imaging, we demonstrate that the bacteroids take up 20-fold more sulfate than the nodule host cells. Furthermore, we show that nitrogenase biosynthesis relies on high levels of imported sulfate, making sulfur as essential as carbon for the regulation and functioning of symbiotic nitrogen fixation. Our findings thus establish the importance of sulfate and its active transport for the plant-microbe interaction that is most relevant for agriculture and soil fertility. This article provides a comprehensive explanation for the importance of the nodule specific sulfate transporter (SST1) and the role of sulfate by dissecting the sulfur distribution across the nodule tissue and directly linking sulfate incorporation to nitrogenase biosynthesis.

Department of Ecogenomics and Systems Biology
Plant, Cell and Environment
Publication date
Publication status
E-pub ahead of print
Peer reviewed
Austrian Fields of Science 2012
106022 Microbiology, 106031 Plant physiology, 106002 Biochemistry
legume nodules, nanoSIMS, nitrogen fixation, stable isotope labeling, sulfur deficiency, symbiotic sulfate transporter (SST1)
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