Inducing Plastid Terminal Oxidase for Photoprotection

粮食安全是人类面临的最大挑战之一。人口增长和饮食变化正在增加粮食需求，而人类活动引起的气候变化正在使天气变得难以预测，威胁到作物生产。干旱、洪水、高温和低温，即使是相对较短的时间，都会影响农作物的最终产量。在此背景下，迫切需要培育既高产又能承受环境胁迫的作物。环境胁迫的主要目标之一是光合作用。光合作用是植物捕获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。光合作用是我们所有食物的最终来源。当植物受到压力时，叶子吸收的能量和光合作用所消耗的能量之间就会出现不平衡。当这种情况发生时，多余的能量会导致有害分子活性氧（ROS，包括漂白剂、过氧化氢）的产生。这些活性氧会破坏细胞，破坏细胞膜、蛋白质和DNA。在整个植物界，我们看到了一系列有助于保护植物免受活性氧侵害的机制。植物含有高浓度的抗氧化剂，如维生素A和E，它们是人类饮食的重要组成部分。它们还具有阻止ROS产生的调节机制。其中一个例子是质体末端氧化酶（PTOX），迄今为止只在少数耐极端胁迫的植物中自然存在。在耐胁迫植物中，如白菜相对盐芥（Eutrema salsugineum，属于芸苔科），PTOX作为光合作用的安全阀，以水的形式无害地消散多余的能量，避免ROS的产生。然而，PTOX尚未在普通作物物种中发现。以前试图通过基因改造在其他物种中诱导PTOX的尝试不仅失败了，而且使事情变得更糟，增加了而不是防止了压力。在最近的一项突破中，我们已经证明有可能在一个新物种中诱导PTOX的活性，通过将蛋白质靶向一个叫做类囊体腔的特定细胞室。管腔靶向PTOX不是组成活性，但在应激条件下变得活跃。我们已经证明，之前在盐芥中看到的这种活性，可以转移到另一种芸苔属植物，泰利芥。在这项资助中，我们将研究压力诱导的腔内靶向PTOX激活所必需的因素。我们还将尝试用同样的方法，在重要的作物物种中诱导PTOX——油菜（另一种芸苔属植物）、大豆（一种豆科植物）和小麦和大麦（禾草类植物）。如果成功，这种方法将为产生具有更好的抗逆性的作物铺平道路，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.