Genetic engineering of higher leaf vein density in rice towards improved yield

到2050年，世界人口预计将达到91亿。当目前有10亿人长期处于饥饿状态时，我们将如何养活这些人口？水稻和小麦提供的食物比其他任何作物都多。由于几个原因，这些作物的大幅增产将很难实现。这两个物种都利用了被称为C3的光合作用的最常见变体，由于一种被称为光呼吸的过程，特别是在高温和缺水的环境中，光合作用的产量都降低了。全球变暖已经加剧了这些问题。世界范围内正在努力探索通过改造C4光合作用植物的典型性状来减少水稻和小麦光呼吸的可能性。转化为C4性状可以使产量提高到接近玉米的水平，C4植物在高温下的光合作用产量比水稻高50%。C4植物将二氧化碳集中在叶脉周围的束鞘细胞中，从而避免光呼吸。由于C4光合作用与叶脉有关，C4植物需要高叶脉密度以获得高光合产物产量。虽然对C4光合作用的分子遗传学基础的了解取得了相当大的进展，但对高脉密度的基本要求尚未解决。我们已经率先证明，通过操纵植物激素生长素的运输和分布，可以在双科植物中获得更高的静脉密度。我们现在已经获得了单子叶植物的类似证据，包括小麦和水稻。我们还证明，进入未确定的地面细胞强烈影响对生长素的反应和更高静脉密度的形成。综上所述，这使我的实验室在培育基因诱导的叶脉密度更高的水稻植株方面处于有利地位。我们建议从四个平行的方向来解决这个问题；增加诱导生长素的水平，增加对生长素的感知，减少生长素的管道化，最后，提供更多的未成熟的地面细胞，这些细胞可以通过静脉形成对生长素作出反应。我们还试图鉴定与C4叶脉典型的增强束鞘层分化有关的基因。这个程序将使我们对单子片植物中调节静脉模式的参数有一个基本的了解。更重要的是，目前的数据与我们正在采用的平行方法一起，为提高水稻叶脉密度提供了很高的成功机会。这将使我们能够与国际合作，并有可能获得资助，来改造C4水稻，最终也改造C4小麦，以增加粮食产量。这个项目对加拿大有几个潜在的长期好处。首先，它可能成为解决未来世界粮食安全问题的重大贡献，这从人道主义、经济和政治角度都对加拿大感兴趣。其次，该项目的成果也可以应用于加拿大的农作物，主要是在加拿大大规模种植的小麦和油菜。这些作物经历高温和周期性干旱，导致产量下降，主要是由于光呼吸作用。

The world’s population will reach an estimated 9.1 billion by the year 2050. How will we feed this population when currently 1 billion people already are chronically hungry? Rice and wheat provide more food than any other crops. Big production increases in these crops will be hard to achieve for several reasons. Both species, utilizing the most common variant of photosynthesis known as C3, have reduced photosynthetic yield due to a process known as photorespiration especially in environments with high temperatures and reduced access to water. Global warming is already exacerbating these problems.There is a world-wide effort underway to explore the possibility of reducing photorespiration in rice and wheat by engineering traits typical of plants utilizing C4 photosynthesis. A conversion to C4 traits could increase yields to levels approaching that of maize, a C4 plant, whose photosynthetic yield at higher temperatures is 50% higher than rice. C4 plants concentrate CO2 in bundle sheath cells surrounding leaf veins, thereby avoiding photorespiration. Since C4 photosynthesis is associated with leaf veins, C4 plants require a high vein density for a high yield of photosynthates. While considerable advances have been made in the understanding of the molecular genetic basis of C4 photosynthesis, the fundamental requirement of a high vein density is unresolved. We have pioneered work demonstrating that higher vein density can be obtained in dicot plants by manipulating transport and distribution of the plant hormone auxin. We have now obtained similar evidence for monocots, including wheat and rice. We have also demonstrated that access to undetermined ground cells strongly influences the response to auxin and the formation of higher vein density. Taken together, this puts my laboratory in an excellent position to generate rice plants with genetically induced higher leaf vein density. We propose to approach this problem from four parallel directions; to increase levels of inductive auxin, to increase to the perception of auxin, to reduce canalization of auxin and finally, to provide a larger number of immature ground cells that can respond to auxin by vein formation. We also seek to identify genes involved in the differentiation of the enhanced bundle-sheath layer typical of C4 leaf veins.This program will allow us to generate a basic understanding of the parameters that regulate vein patterning in monocot plants. More important, present data together with the parallel approaches that we are taking provide high chance of success in enhancing leaf vein density on rice. This will allow us to collaborate with and potentially get funded by international efforts to engineer C4 rice and ultimately also C4 wheat to increase food production. There are several potential long-term benefits of this program to Canada. First, it may become a substantial contribution to addressing future food security in the world, which is of interest to Canada from humanitarian, economical and political perspectives. Second, the outcomes of this program can also be applied to Canadian crops, primarily wheat and canola, grown in large scale in Canada. These crops experience high temperatures as well as periodic drought, leading to reduced yield in large part due to photorespiration.