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

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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.