Our understanding of sulfur metabolism in plants lags far behind that of nitrogen and carbon metabolism. Sulfur metabolism can now be explored via molecular-genetic approaches, which have recently shown how plants reduce sulfate and synthesize the essential amino acid methionine (Met). There has been less progress in understanding plant sulfur metabolism from Met onwards. This area is a hub of metabolism because sulfur-and one-carbon pathways intersect at the level of Met and its metabolites S-adenosylmethionine and S-methylmethionine (SMM). It is also central to environmental biochemistry because Met and SMM are the starting points for the synthesis of dimethylsulfoniopropionate (DMSP), a compound that protects plants from salt stress and is of major significance to the biogeochemical sulfur cycle and global climate. The lack of understanding of sulfur metabolism from Met onwards is the rationale for this project, which addresses two related problems: the functions of SMM, and the biosynthetic pathway of DMSP in flowering plants. By clarifying the functions of SMM we will advance knowledge of how plants control their contents of Met, an essential amino acid in human and animal nutrition. By show how some plants have evolved a novel pathway to convert SMM into the protective compound DMSP we will advance understanding of basic mechanisms of stress resistance and of the biochemistry of the sulfur cycle. Two postdoctoral students and a Ph.D. student will be trained.
