Sulfur Metabolism in Plants

Abstract Sulfur is an essential element found in plants in a variety of compounds with many different functions. The sulfur‐containing amino acids cysteine and methionine are essential components of proteins. Sulfur is the active component of many coenzymes, such as iron–sulfur centres, lipoic acid or coenzyme A, and metabolites important for plant defence against biotic and abiotic stress, for example glutathione or glucosinolates. In addition, the sulfur‐containing natural compounds glucosinolates and alliins are important for human food and health. Sulfur is taken up as inorganic sulfate from the soil, reduced to sulfide and incorporated into amino acid cysteine, which serves as a donor of reduced sulfur for other metabolites. Sulfate uptake and assimilation are highly regulated by sulfur supply and demand. Research into plant sulfur nutrition has been boosted by the growing appearance of sulfur‐deficiency syndromes in crops, which lowers grain quality and increases disease susceptibility, caused by a reduction in atmospheric sulfur dioxide emissions. Key Concepts Sulfur is an essential nutrient for all organisms, and a large portion of sulfur in nature exists in bioorganic compounds. Sulfur is a very mobile element moving between oceans, atmosphere and terrestrial ecosystems often undergoing transformations of its chemical state in the biosphere. In the sulfate assimilation pathway, sulfate taken up by sulfate transporters, is reduced to sulfide and incorporated into bioorganic compounds, forming the amino acid cysteine. The sulfate assimilation pathway is present in bacteria, fungi, plants and algae but not in metazoans or in most parasitic microorganisms. Sulfate assimilation is a highly regulated process requiring coordination with carbon and nitrogen metabolism across a range of tissues and in multiple subcellular organelles. Sulfate assimilation is regulated in a demand‐driven manner through a robust transcriptional network, but also includes post‐transcriptional and post‐translational regulation. In Arabidopsis, Sulfur LIMitation 1 (SLIM1) is a transcriptional activator of many sulfate transporters and genes involved in the sulfur starvation response. The sulfur‐containing tripeptide glutathione is important as redox buffer, acts as a storage and transport form of reduced sulfur and regulates the cell cycle and protein translation. Sulfur‐containing natural compounds glucosinolates and alliins are responsible for the smell and taste of cruciferous and allium family vegetables and for the benefits of these vegetables for human health.