How do eukaryotic phytoplankton produce the most abundant organo-sulphur compound in the world's oceans?

There is a molecule, called dimethylsulphoniopropionate (DMSP) which is made in very large amounts - a billion tons per year, worldwide - by myriads of tiny single-celled marine plankton, many seaweeds and a few land plants that live near the seaside. In some of these, most of the sulphur and much of the carbon is in the form of this molecule, but the influence of DMSP is even more wide-ranging than that. Despite its abundance, there is no clear agreement as to what is the function of the DMSP - maybe it buffers the cells from the saltiness of the sea, maybe it acts as a defence compound against attack by predators, maybe it protects against ultraviolet light. - maybe it is a molecular jack of all trades.
DMSP is not only interesting in its own right, but it also has a chemical legacy, since it is the parent compound for other molecules that are also very important. When the plant-like organisms that make DMSP release it into the environment, either by leakage, or more dramatically when they are lysed by viruses or microscopic animals, it is used as a tasty food source by the teeming marine bacteria and some fungi in a process of DMSP catabolism. This represents a massive part of the global sulphur cycle, but even that is not all.
One of the DMSP breakdown products is a gas, called dimethyl sulphide (DMS), which has important environmental impacts in its own right. Of the 300 million tons of DMS made each year in the oceans and their margins, around 10% escapes into the atmosphere, where it gets oxidised to sulphate and sulphuric acid. These molecules act as "Cloud Condensation Nuclei", which cause clouds to form, just as specks of dust can start crystals growing in crystal gardens. This occurs on such a scale that it is responsible for much of the cloud cover over the seas and oceans and may affect the amount of solar heat and light that arrives on Earth - a form of "Global Dimming". The DMS also acts as a signal for many marine animals - birds, seals and tiny crustaceans - since it is a chemical signature for their plankton food supplies. Also to us, as Homo sapiens, DMS is part of the smell of the seaside, especially when there is a lot of seaweed about.
Although there have been some nice preliminary studies in which the general pathways for DMSP synthesis have been described, none of the purified enzymes or corresponding genes have been identified in any DMSP-producing organism. This lack of knowledge has made it hard to work out unambiguously what are the true functions of DMSP.
This study focuses on one group of phytoplankton, collectively known as diatoms, which produce large amounts of DMSP. These microscopic plant-like organisms are abundant in the world's oceans - all told, they make up a quarter of Earth's plant life by weight and they produce around the same proportion of the oxygen that we breathe.
We have very recently identified four key genes in diatoms that we strongly believe encode enzymes that are involved in DMSP production. We now plan to study the exact functions of these genes and the enzymes that they encode by making mutants that no longer make DMSP and, conversely, by engineering strains that over-produce it. This will allow us, for the first time in any organism, to figure out with certainty what are the functions of this key molecule. We will also discover how the genes are expressed; are they switched on all the time, or do they respond to (for example) various stresses in the environment? Does this differ between different species? Not only will this provide new insights on the role(s) of DMSP in diatoms, but our results should shed light on the mechanisms that are involved in this process in other important marine organisms that make this key molecule. Such studies will only strengthen our ability to assess the effects of future environmental changes on this crucial biosynthetic process.

This project is primarily driven by the need to address a fundamental gap in the knowledge of how "DMSP", the precursor molecule for the climatically active gas "DMS", is made and what is its role in the organisms that produce it. The field of research into biological DMS release is a well funded and publicised area of NERC-based research, exemplified in NERC's Summer 2009 edition of Planet Earth, as a special feature report entitled " Sea, cells, genes, smells, on the sea shore", highlighting this research. Indeed in this report the editor specifically choose to highlight the phrase "It is astonishing that we still do not know of a single gene for DMSP synthesis", clearly emphasising the potential impact of this proposal.

The "diatoms" being studied in this proposal are ubiquitous in the world's oceans, are literally the drivers of many of the Earth's most vital processes, and are also of significant interest to bioindustry. DMSP synthesis enzymes provide a novel set of genes that could provide stress (drought) tolerance to crop plants. Parallel studies have found genes for synthesizing the tertiary nitrogen analog to DMSP, glycine betaine, confers stress tolerance in Arapidopsis and overexpression of antioxidant enzymes have been used to improve salinity tolerance. DMSP is believed to be a multi-faceted anti-stress molecule providing osmoprotectant, cryoprotectant, and antioxidant properties. It therefore has great potential to enhance stress tolerance in crops. Importantly, Mock is also involved in work to overexpress genes from diverse diatoms involved in lipid metabolism in higher plants therefore is in a great position to translate discoveries from the proposed work towards development of new strains of transgenic crops.

As we have set out in the Pathway to Impact, there is clear evidence that the media - and indeed NERC - find our work to be interesting and, in some cases amusing and provocative. This was exemplified by the media kerfuffle that followed the publication of the Todd et al (2007) Science paper, with appearances on TV, both in the UK and in Germany, radio interviews and press reports throughout the world. This stemmed from the public interest in "Cloning the smell of the seaside" and in the influence of DMS on climate and animal behaviour. We regard this media attention as invaluable because it directly allows the public to see that their investment has outputs that although are not immediately to the financial advantage of UK PLC, do add to the bank of human knowledge in ways to which they can relate.

We have capitalised on this popularity in our Pathway to Impact that focuses on delivering the outcome and the conduct of this, and related work to our younger generation. Partly through the auspices of the SAW (Science Art Writing) scheme (http://www.sawtrust.org/), we will involve several local primary schools near UEA. Also, several of the past and planned events build on the "Beacon of Public Engagement" award "CueEast" (Community University Engagement East) to UEA and its partners. In addition, we will also target school students at 6th form level and key stages 3 and 4, our labs playing host to a few such selected, local 6th form students.

Finally, we will, of course, continue to disseminate our findings through the usual channels of publications, and will also strive to include other publications in journals that have a wider and less specialised audiences.