Rhizosphere bacterial sulfatases and their control by interactions with plants

植物生长需要硫，但农业土壤中的大部分硫以结合形式(硫酸酯)存在，可以被一些细菌利用，但不能直接被植物利用。其中许多细菌与植物根部密切相关，在根部本身和紧邻其周围的土壤(根际)形成密集的群落。它们受到植物的积极营养，植物利用光合作用产生糖和氨基酸，从根部释放出来促进细菌生长，反过来，许多与根相关的细菌通过动员土壤中的矿物质营养(包括硫)来促进植物的生长。这种相互作用依赖于植物和微生物之间的交流网络，由负责土壤中某些功能的细菌专业组负责，植物使用特定的信号来刺激这些细菌产生它所需的营养。该项目将研究根际硫代谢的两个主要方面。首先，我们将研究哪些细菌家族在促进土壤中结合硫的释放以供植物利用方面起重要作用。由于许多土壤细菌不能在实验室中培养，我们将首先建立一个来自可培养土壤细菌的硫酸酯利用基因数据库，这些细菌可以代谢硫酸酯。然后，我们将使用这个数据库来调查英国种植的三种最重要的农作物--小麦、大麦和油菜--根际微生物群落的总体情况。这将为鉴定我国主要农作物根际硫酸酯代谢最重要的细菌种类提供重要的新信息。为了增加这一数据的预测能力，我们将在从彭赞斯到阿伯丁的英国各地的田间试验点，在这些作物最具商业价值的品种的根际验证这些发现。在确定了在土壤硫酸酯代谢中最活跃的细菌后，下一步是确定植物如何控制它们的活动。我们的初步发现表明，植物可以促进硫酸酯代谢最重要的细菌酶-芳基硫酸酯酶的产生，并且一旦产生也可以刺激其活性。这两个过程发生的机制将在包括农作物和其他物种在内的一系列植物中进行研究，方法是分离负责刺激芳基硫酸酯酶活性的拟南芥蛋白，并初步阐明植物根分泌物如何超越正常的细菌控制芳基硫酸酯酶的产生。这一结果将为植物如何控制根际环境中的养分循环提供新的见解，在促进英国可持续农业方面具有潜在的应用前景。

Plants require sulfur for growth, but much of the sulfur in agricultural soils is present in a bound form ('sulfate esters') that can be used by some bacteria, but not directly by plants. Many of these bacteria live in close association with plant roots, forming dense communities on the root itself and in the soil immediately surrounding it (the 'rhizosphere'). They are actively nourished by the plant, which uses photosynthesis to produce sugars and amino acids that are released from the root to promote bacterial growth, and in return many of these root-associated bacteria promote plant growth by mobilizing mineral nutrients (including sulfur) from the soil for plant utilization. This interaction relies on a network of communication between plants and microbes, with specialist groups of bacteria responsible for certain functions in the soil, and the plant using specific signals to stimulate these bacteria to produce the nutrients it needs. This project will examine two main aspects of sulfur metabolism in the rhizosphere. First, we will investigate which bacterial families are important in promoting the release of bound sulfur from the soil for plants to use. Because many soil bacteria cannot be cultivated in the laboratory, we will start by establishing a database of sulfate ester utilization genes from cultivable soil bacteria that can metabolize sulfate esters. We will then use this database to investigate the overall microbial community in the rhizosphere of the three most important agricultural crops that are grown in the United Kingdom, wheat, barley and oilseed rape. This will provide vital new information to identify the most important bacterial species for sulfate ester metabolism in the rhizosphere of our major crops. To increase the predictive power of this data we will then validate these findings in the rhizospheres of the most commercially important cultivars of these crops, on field trial sites across the UK from Penzance to Aberdeen. Having identified the bacteria that are most active in soil sulfate ester metabolism, the next step is to characterize how plants control their activity. Our preliminary findings show that plants can promote the production of the most important bacterial enzyme for sulfate ester metabolism, arylsulfatase, and can also stimulate its activity once produced. The mechanisms by which these two processes occur will be investigated in a range of plants, including both crops and other species, by isolating the Arabidopsis protein that is responsible for stimulating arylsulfatase activity, and taking the first steps in elucidating how plant root exudates can override the normal bacterial control of arylsulfatase production. The results will provide new insights into how plants control nutrient cycling in the rhizosphere environment, with potential applications in promoting sustainable agriculture in the United Kingdom.