Inducing Plastid Terminal Oxidase for Photoprotection

粮食安全是人类面临的最大挑战之一。不断增长的人口和不断变化的饮食正在增加粮食需求，而此时人类引发的气候变化正在使天气变得更难预测，威胁到作物产量。干旱、洪水、高温和低温，即使是相对较短的时期，都可能损害最终的作物产量。在这种背景下，迫切需要培育出既高产又能耐受环境胁迫的作物。环境胁迫的主要目标之一就是光合作用。光合作用是植物捕捉光能并利用光能固定空气中的二氧化碳，从而产生糖的过程。光合作用是我们所吃的所有食物的最终来源。当植物受到压力时，叶子吸收的能量和可用于光合作用的能量之间可能会出现不平衡。当这种情况发生时，多余的能量可能会导致有害分子的产生，称为活性氧物种(ROS；包括漂白剂，例如过氧化氢)。这些ROS可以破坏细胞，破坏细胞膜、蛋白质和DNA。在整个植物王国中，我们看到了一系列有助于保护植物免受ROS伤害的机制。植物含有高浓度的抗氧化剂，如维生素A和维生素E，它们是人类饮食的基本成分。他们还拥有防止ROS产生的监管机制。其中一个例子，到目前为止，只在少数极端耐受胁迫的植物中自然出现，被称为叶绿体末端氧化酶，或PTOX。在耐胁迫植物中，如甘蓝相对盐生水芹(Eutrema salsugineum，十字花科)，PTOX作为光合作用的安全阀，以水的形式无害地消耗多余的能量，避免ROS的产生。然而，PTOX还没有在常见的作物物种中被发现。以前使用基因修饰在其他物种中诱导PTOX的尝试不仅失败了，而且还使情况变得更糟，增加而不是防止了压力。在最近的一项突破中，我们证明了通过将蛋白质靶向称为类囊体腔的特定细胞室，在一个新的物种中诱导PTOX的活性是可能的。腔靶向PTOX在结构上不是活性的，但在应激条件下变得活性。我们已经证明，这种以前在盐水芹中看到的活性，可以转移到另一种十字花科植物--水芹上。在这项资助中，我们将研究应激诱导的管腔靶向PTOX激活所必需的因素。我们还将尝试使用相同的方法，在重要的作物物种--油菜(另一种油菜)、大豆(一种豆科植物)以及小麦和大麦(草)中诱导PTOX。如果成功，这种方法将为培育耐逆性更强的作物铺平道路，从而在极端环境条件下提高作物产量。

Food security is one of the greatest challenges facing humanity. Growing populations and changing diets are increasing food demand at a time when human-induced climate change is making weather less predictable, threatening crop production. Episodes of drought, flooding, high and low temperatures, even for relatively short periods, can all undermine final crop yields. Against this background, there is an urgent need to breed crops which combine high productivity with the ability to tolerate environmental stress.One of the main primary targets of environmental stress is photosynthesis. Photosynthesis is the process by which plants capture light energy and use that energy to fix carbon dioxide from the air, producing sugars. Photosynthesis is the ultimate source of all the food we eat. When plants are stressed, imbalances can occur between the amount of energy a leaf absorbs and the amount that can be used in photosynthesis. When this happens, the excess energy can result in the production of harmful molecules called reactive oxygen species (ROS; including for example the bleach, hydrogen peroxide). These ROS can damage the cell, destroying membranes, proteins and DNA.AAcross the plant kingdom we see a range of mechanisms that help protect plants from ROS. Plants contain high concentrations of antioxidants, such as Vitamins A and E, which are essential components of the human diet. They also possess regulatory mechanisms that prevent ROS production. One example, so far only seen naturally in a handful of extreme stress tolerant plants, is called the Plastid Terminal Oxidase, or PTOX. In stress tolerant plants, such as the cabbage relative salt cress (Eutrema salsugineum, in the brassica family), PTOX acts as a safety valve for photosynthesis, dissipating excess energy harmlessly as water, avoiding ROS production. PTOX has not however been seen in common crop species. Previous attempts to use genetic modification to induce PTOX in other species have not only failed, they have made matters worse, increasing rather than preventing stress.In a recent breakthrough, we have shown it is possible to induce activity of PTOX in a new species, by targeting the protein to a particular cellular compartment called the thylakoid lumen. Lumen-targeted PTOX is not constitutively active, but becomes active under stress conditions. We have shown that this activity, seen previously in salt cress, can be transfered to another brassica species, thale cress. In this grant, we will examine the factors that are necessary for the stress-induced activation of lumen-targeted PTOX. We will also attempt, using the same approach, to induce PTOX in important crop species - oilseed rape (another brassica), soybean (a legume) and wheat and barley (grasses). If successful, this approach will pave the way to generate crop plants with improved stress tolerance, increasing crop yields under extreme environmental conditions.