Spatial and temporal mapping of the pea root secretome and its control of bacterial rhizosphere colonisation

细菌是简单的单细胞生物体，缺乏动植物高等细胞中的膜结合结构。然而，尽管细菌可能具有不那么复杂的细胞组织，但它们进行的化学反应范围之广，在动植物中是找不到的。细菌负责许多营养物质的循环，如氮气(氮气也被称为氮气，由两个被强三键结合的氮原子组成)，这是一种非常惰性的大气气体。氮气占大气的78%，但非常不活跃，不能直接用作氨基酸、蛋白质和DNA合成所需的氮源。然而，少数细菌可以通过包括细菌和植物在内的各种生物将氮气还原(添加氢气)并将其转化为氨(NH3)，氨很容易被结合到氨基酸中，然后进入生命的所有其他组成部分。在世界上许多地方，植物生长的限制是氨或相关化合物的氮供应，而植物反过来又支持动物的生命。由于高达65%的有效氮(如氨)来自细菌，这使得它们对地球上的生命至关重要。在细菌内部，大部分氮实际上是由一个被称为根瘤菌科的家族产生的。这组引人注目的细菌与豆科植物形成了共生关系(双方都受益)，导致了根瘤的形成(在豌豆植物上，这些根瘤是2-3毫米的鳞茎，通过拔出植物并检查其根可以很容易地看到)。根瘤菌保存在根瘤内，植物为它们提供了理想的环境(低氧气和大量能量)，在那里它们可以将氮气还原为氨。氨被提供给植物作为氮源，这就是为什么这被称为共生相互作用。这意味着植物确实需要向土壤中添加任何氮素，并使其快速生长。这项研究的目的是了解细菌(根瘤菌)在一个称为定殖化的过程中如何首先与根相关联。如果细菌要继续诱导植物形成根瘤，并将氮气还原为氨，这是至关重要的一步。许多根瘤菌具有令人满意的生物学特征，如将大量氮气固定为氨的能力，但不太受欢迎的根瘤菌在形成根瘤方面处于竞争地位。我们想要了解一些菌株“适合度”的遗传基础，这使得它们能够在竞争中击败其他菌株。

Bacteria are simple single celled organisms that lack the membrane bound structures found in higher cells of plants and animals. However, while bacteria may have a less complex cellular organisation they carry out a huge range of chemical reactions not found in plants and animals. Bacteria are responsible for the cycling of many nutrients such as N2 (N2 is also known as nitrogen gas and consists of two nitrogen atoms bound by a strong triple bond), which is a very inert atmospheric gas. N2 makes up 78% of the atmosphere but is very unreactive and cannot be used directly as a source of nitrogen, which is needed for amino acid, protein and DNA synthesis. However, a small number of bacteria can reduce (add hydrogen) to N2 and convert it into ammonia (NH3), which is readily incorporated into amino acids and then all the other building blocks of life, by a wide range of organisms including bacteria and plants. In many parts of the world the limitation to growth of plants, which in turn support animal life, is the supply of nitrogen as ammonia or related compounds. Since up to 65% of available nitrogen (eg ammonia) comes from bacteria this makes them essential for life on earth. Within the bacteria, most of the nitrogen is actually produced by one family known as the Rhizobiacea. This remarkable group of bacteria form a symbiotic association (both partners benefit) with plants of the legume family, that results in the formation of root nodules (on pea plants these are 2-3 mm bulbs that can easily be seen by pulling up a plant and inspecting its roots). The rhizobia are held inside the nodules where the plant provides them with an ideal environment (low O2 and lots of energy) in which they can reduce N2 to ammonia. The ammonia is supplied to the plant as its nitrogen source so this is why this is known as a symbiotic interaction. It means that the plant does need any nitrogen added to the the soil and enables rapid growth. The purpose of this research is to understand how the bacteria (rhizobia) first associate with roots in a process called colonisation. This is a vital step if the bacteria are going to go on to elicit nodule formation by the plants and reduce N2 to ammonia. Many rhizobia with desirable argonomic features, such as the ability to fix large amounts of N2 to ammonia, are out competed for nodule formation by less desirable rhizobia. We want to understand the genetic basis for the "fitness" of some strains that allows them to out compete other strains.