Genetic manipulation of photoprotection and photooxidative stress tolerance in rice

所有植物，包括农作物，都需要吸收来自太阳的光能，才能生长、发育并最终生产出水果或谷物等可收获的产品。植物生长需要光，光合作用也需要光，光合作用中光与二氧化碳和水结合，合成糖。可利用的光量不能由植物控制，取决于气候因素，光合作用可能会受到光的限制，也可能会吸收超过需要的光。当太多的光被吸收或‘收获’时，能量将被传递给氧气形成自由基，从而破坏植物组织，甚至导致植物死亡，这是一个真正的危险。有许多运行在分子水平上的机制，它们可以感知多余能量的数量，并在一种称为非光化学猝灭或NPQ的过程中无害地将其消散。一种机制涉及一种名为PSB的蛋白质，这种蛋白质存在于所有植物中，充当光收集和能量消耗之间的“开关”。另一种机制涉及类胡萝卜素分子的合成(特别是叶黄素循环XC类胡萝卜素)，这是一种五颜六色的色素(也存在于所有植物中)。它们也是人类饮食中重要的抗氧化剂。在植物中，它们有双重作用：首先，它们也调节NPQ的过程，“调节”它的持续时间或短或长。其次，它们是叶子中被证明有效的抗氧化剂，可以防止对膜的破坏。到目前为止，这些分子只在模式植物拟南芥中被研究过。确实有必要研究如何将这些特性用于作物，以促进作物的生长和产量，特别是在高温、干旱或寒冷的环境中，在这些环境中，再加上强光，氧自由基可能会造成很大的损害。该项目使用了一种模式作物水稻，其中PSB和XC类胡萝卜素的水平已经通过植物转化程序进行了操纵。之所以选择水稻，是因为它很容易转化，而且有测序的基因组。已经产生了PSB含量升高和降低以及XC类胡萝卜素含量升高和降低的植物。这项提议的目的是测试这些改变对植物吸收和利用光的效率的影响。它们是处于最佳水平，还是我们可以改善它们？其次，这些植物，特别是XC类胡萝卜素水平升高的植物，应该对以膜为目标的胁迫具有增强的抵抗力，例如在寒冷或高温和光照下。我们将寻求对这些压力的更强的容忍度。我们将检查植物膜的生物化学，以找出存在多少更多或更少的耐药性。最后，我们将研究这些植物在类似于谷物生产田地生长的情况下的生长速度和生产潜力。我们将找出提高的抗逆性水平和改变的光利用效率是否为植物付出了代价，或者它是否提供了真正的优势。要问的一个重要问题是，我们在野外看到的自然波动的光线水平是否通过这些过程得到有效转换，或者是否有改进的余地。我们有充分的理由相信，这个项目将表明，我们可以让农作物更能抵抗环境压力。随着农业感受到气候变化的影响，植物对环境胁迫的反应应该变得更加重要。此外，这些过程应有利于所有农作物，包括用于能源作物或生物燃料的作物。

All plants, including crop plants need to absorb light energy from the sun in order to grow, develop and eventually produce a harvestable product such as fruit or grain. Light is needed for plant development and it is also needed in photosynthesis where it is combined with carbon dioxide and water to synthesis sugars. The amount of light available cannot be controlled by the plants and depending on climatic factors, photosynthesis can be limited by light or it can absorb more than it needs. When too much light is absorbed, or 'harvested' there is a real danger that the energy will be passed to oxygen to form radicals which will damage plant tissues and even cause plant death. There are a number of mechanisms operating at the molecular level which sense the amount of surplus energy and 'dissipate' it harmlessly in a process called non photochemical quenching or NPQ. One mechanism involves the protein called PsbS which is present in all plants and acts as a 'switch' between light harvesting and energy dissipation. Another mechanism involves the synthesis of carotenoid molecules (specifically xanthophyll cycle XC carotenoids) which are colourful pigments (also present in all plants). They are also important antioxidants in the human diet. In plants they have a dual role: firstly they too regulate the process of NPQ, 'tuning' it to last a short or a long time. Secondly they are proven and powerful antioxidants in leaves, preventing damage to membranes. So far these molecules have only been investigated in the model plant Arabidopsis thaliana. There is a real need to investigate how these properties could be used in crop plants in order to improve growth and yield especially in stressful situations such as heat, drought or cold where, combined with high light, much damage from oxygen radicals can occur. This project uses a model crop, rice, in which the levels of PsbS and XC carotenoids have been manipulated by plant transformation procedures. Rice was chosen because it is easy to transform and has a sequenced genome. Plants with raised and lowered amounts of PsbS and raised and lowered amounts of XC carotenoids have been produced. The objectives of this proposal are to test the effects of these alterations on the efficiency with which light is absorbed and utilised by the plant. Are they at optimum levels or can we improve them? Secondly these plants, especially with raised levels of XC carotenoids should have an enhanced resistance to stress where membranes are the target, for example cold or heat and in the light. We will look for an enhanced tolerance to these stresses.. We will examine the biochemistry of plant membranes to find out how much more, or less, resistance exists. Lastly we will examine the growth rate and the potential for production of these plants in situations similar to growth in the field for grain production. We will find out whether the enhanced level of resistance to stress and the altered light use efficiency has a cost for the plant, or if it provides a real advantage. An important question to ask is whether the natural fluctuating levels of light we see outside in the field situations is efficiently converted by these processes or whether there is scope for improvement. There is good reason to believe that this project will show that we can make crop plants more resistant to environmental stress. Responses of plants to environmental stress should become more important as the impact of climate change is felt by agriculture. Additionally these processes should be of benefit to all crop plants including those which are used for energy crops or biofuels.