Oh I do like to grow beside the seaside: understanding how and why plants produce DMSP

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Billions of tonnes of the organosulfur compound dimethylsulfoniopropionate (DMSP) are made each year by marine algae, corals and bacteria, but some plants also make this important molecule. DMSP is a key marine nutrient pivotal in global sulfur cycling, as it is the main precursor of the climate-active gas dimethylsulfide (DMS). DMS gives the seaside its distinctive smell and is used by many animals and birds as a chemoattractant associated with their algal food. In the atmosphere, DMS is oxidised to sulfates that accelerate cloud formation over the oceans. These clouds affect the amount of sunlight reaching the Earth's surface and this in turn affects the climate. Sulfur is returned to land in the form of rain, completing the cycle.Production of DMSP and DMS is concentrated at the coast, with saltmarshes being hotspots for DMSP/DMS synthesis and predicted to contribute up to 10% of global DMS emissions. We have recently identified different bacteria and algae in saltmarsh mud that make DMSP, but plants in these habitats (particularly the perennial grass Spartina) are believed to be the major DMSP and DMS producers in saltmarshes. In fact, Spartina has the highest intracellular DMSP concentration of all known plants, which is far in excess of that in most DMSP-producing bacteria and algae. DMSP production likely protects plants from environmental stresses associated with growing at the seaside, such as salinity and nutrient limitations, but this has not been fully tested or established. Interestingly, some Spartina species cannot make DMSP (even though they grow well at the coast), while some crop plants (such as tomato and maize - which don't usually grow at the coast) are able to produce DMSP when grown under particular environmental stresses like high salinity or drought. Our understanding of why plants produce DMSP is therefore lacking and this is something we will investigate here, focussing on specific Spartina species that either produce DMSP or do not and the crop plant tomato. We will establish which developmental triggers and environmental conditions cause plants to synthesise DMSP and will determine what benefits DMSP production confers to plants. Furthermore, we will study the natural production and turnover rates of DMSP and DMS by Spartina growing in saltmarshes over a season. This will allow us to better understand and predict the significance of such environments for the production of these influential compounds.It is also unclear how plants actually produce DMSP. Our work with bacteria and algae identified different biosynthetic routes for DMSP synthesis and the key genes and enzymes involved. Based on this previous work, we have now identified candidate genes responsible for DMSP production in plants. We will mutate these genes and characterise their enzyme products to confirm their function in the plant DMSP synthesis pathway. We will also study how these plant genes are expressed, i.e. when and in which specific tissues and cellular compartments, and regulated by which environmental conditions. Currently the contribution of plants to global DMSP and DMS production is likely vastly underestimated since few plants have been tested for DMSP under appropriate conditions. Knowing key plant DMSP synthesis genes and factors regulating them will allow us to evaluate better the diversity of plants capable of this process and their potential impacts on environmental production.Overall, this work will allow us to understand how, why and where plants produce DMSP and how plants contribute to global DMSP and DMS production. This will allow us to predict better the impacts of DMSP and DMS on the natural environment and climate. Harnessing the protective effects of DMSP production in plants may also allow us to improve crop growth and productivity under stressful conditions and thus enhance food security in the future.