Enhanced capacity for grain filling in wheat: WHEASE

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Wheat is one of world's main crops. The starch contained in wheat grains is a vitally important source of dietary calories for billions of people. Demand for food is rising as world population grows and dietary habits change, but despite the best efforts of crop breeders the world-wide yields of wheat are not increasing at the necessary rates to keep up with future demands. Urgent efforts are required to understand the limitations on yield and to suggest new ways in which yield may be increased through crop breeding. One major factor that determines wheat yield is the capacity of the developing grains to make starch from the sugars they receive from the leaves. If the capacity for starch synthesis in the grains is low, the plant will have relatively small numbers of small grains, and much of the sugar produced by photosynthesis in the leaves will be wasted. Scientists have a relatively good understanding of the way in which sugars are converted into starch in the developing grain. It is possible to identify some components of this process that may limit how much starch is made. If amounts of these components (enzymes called ADPglucose pyrophosphorylase and starch synthase) could be increased, starch accumulation and hence grain number and size might be increased. We will attempt to increase amounts of these enzymes in two ways. First, we will study large numbers of different kinds of wheat, including ancient varieties and wild ancestors, to see whether any of them already have large amounts of either of the two enzymes, or different genes for these enzymes. Second, we will use transgenic techniques to increase amounts of the two enzymes by adding extra gene copies. For both of these approaches, we will assess whether high activities of the enzymes are associated with high yields. We expect that this work will produce information that will help crop breeders and biotechnologists to increase wheat yield. We will also work closely with other scientists trying to increase sugar production in wheat leaves, using the same kinds of approaches. Together, we hope to be able to increase both leaf sugar production and the capacity for grains to convert sugars to starch in a single plant. This plant is expected to have a high yield, and to enable us to understand better how we can breed higher-yielding crops in future.