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

每年有数十亿吨的有机硫化合物二甲基磺基丙酸酯（DMSP）由海藻、珊瑚和细菌产生，但一些植物也会产生这种重要的分子。DMSP是全球硫循环的关键海洋营养物，因为它是气候活性气体二甲基硫（DMS）的主要前体。二甲基硫醚赋予海滨独特的气味，被许多动物和鸟类用作与藻类食物相关的化学引诱剂。在大气中，二甲硫醚被氧化成硫酸盐，加速了海洋上空云层的形成。这些云影响到达地球表面的阳光量，这反过来又影响气候。硫以雨水的形式返回陆地，完成循环。DMSP和DMS的生产集中在海岸，盐沼是DMSP/DMS合成的热点，预计将占全球DMS排放量的10%。我们最近已经确定了不同的细菌和藻类在盐沼泥，使DMSP，但在这些栖息地的植物（特别是多年生草米草）被认为是主要的DMSP和DMS生产盐沼。事实上，在所有已知植物中，米草具有最高的细胞内DMSP浓度，这远远超过了大多数产生DMSP的细菌和藻类。DMSP的生产可能会保护植物免受与海滨生长相关的环境压力，例如盐度和营养限制，但这一点尚未得到充分测试或证实。有趣的是，一些米草属物种不能产生DMSP（即使它们在海岸生长良好），而一些作物（如番茄和玉米-通常不生长在海岸）在特定的环境压力下生长时能够产生DMSP，如高盐度或干旱。因此，我们对植物产生DMSP的原因缺乏了解，这是我们将在这里进行调查的内容，重点关注特定的米草属物种，要么产生DMSP，要么不产生DMSP，以及作物番茄。我们将确定哪些发育触发因素和环境条件导致植物合成DMSP，并确定DMSP生产对植物的益处。此外，我们将研究自然生产和周转率的DMSP和DMS米草生长在盐沼超过一个赛季。这将使我们能够更好地理解和预测这种环境对这些有影响的化合物的生产的重要性。目前还不清楚植物实际上是如何生产DMSP的。我们对细菌和藻类的研究确定了DMSP合成的不同生物合成途径以及所涉及的关键基因和酶。基于这一先前的工作，我们现在已经确定了负责植物中DMSP生产的候选基因。我们将对这些基因进行突变并检测其酶产物，以确定它们在植物DMSP合成途径中的功能。我们还将研究这些植物基因是如何表达的，即何时以及在哪些特定组织和细胞区室中表达，以及受哪些环境条件的调节。目前，植物对全球二甲氧基磺隆和二甲硫醚产量的贡献可能被大大低估，因为很少有植物在适当条件下接受过二甲氧基磺隆测试。了解植物DMSP合成的关键基因及其调控因子将使我们能够更好地评估能够进行这一过程的植物的多样性及其对环境生产的潜在影响。总体而言，这项工作将使我们了解植物如何，为什么和在哪里产生DMSP以及植物如何对全球DMSP和DMS生产做出贡献。这将使我们能够更好地预测DMSP和DMS对自然环境和气候的影响。利用DMSP生产对植物的保护作用，还可以使我们在压力条件下改善作物生长和生产力，从而加强未来的粮食安全。

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.