Identification of a dominant glaucous inhibitor in wheat (Iw1) and its effect on yield and senescence

If you walk through a park in the early morning or after rain has fallen you will notice drops of water on the surface of the grass or the leaves in the trees. Water drops tend to roll off the leaves and are not absorbed by the plant since leaves and all plant surfaces are sealed by a thin continuous layer that repels water. This layer, called the cuticle, is of great importance as it protects the inside of the plant (clean and humid) from the harsh external environment (dirty and dry). Without a cuticle, plants would not survive on land. The cuticle is made up of a series of different types of waxes that vary depending on the plant species examined. These different wax compositions greatly affect how the plant can interact with the environment, for example, by impeding certain insects from recognizing the plant. They also determine the physical properties of the plant, such as its color, by affecting how much sunlight is captured or reflected from the plant. This is very important as the amount of sunlight reaching the plant determines how much energy the plant can produce via photosynthesis. In crops such as wheat, this has significant implications as increases in energy production lead to higher grain yields. Despite these apparent benefits, excess sunlight can also have negative effects on the plant. Therefore, the cuticle pays a key role in the plant by optimizing light capture whilst securing its survival and reproduction. This is a complex balancing act that will change depending on the environmental conditions in which the plant is grown. A promising strategy to produce wheat varieties that can provide higher yields and adapt to different environmental conditions is to modify the cuticular wax composition. This is an important objective as our society looks for ways to produce more food with less energy and water input. This is especially relevant as the threat of global warming materializes over the next decades. Our ability to develop these improved varieties will depend on our understanding of the genes controlling or regulating cuticular wax composition in wheat as our current knowledge is limited and incomplete. We need to do better, and fast. We have recently identified a region of the wheat genome that affects the amount of cuticular wax deposited in leaves and stems. This region contains several hundred or even thousands of genes, but provides an initial entry point to start understanding the genetic components that determine this important trait. Interestingly, we also discovered that this same region has a significant effect on grain yield and on the plant's aging process. These observations could be explained in two possible ways: there is a single gene within this region controlling cuticular wax which indirectly affects grain yield and aging or alternatively, the individual genes affecting these traits are completely independent and unrelated. It is important to decipher this so that we can determine the cause and the consequences of these important traits. In this proposal we will identify the gene responsible for the change in cuticular wax deposition in wheat and test whether this gene also affects yield and plant aging under UK environmental conditions. We will also develop wheat varieties with modified cuticular wax and test how they perform under field conditions compared to unmodified control plants. Identifying the molecular nature of the gene responsible for cuticular wax deposition in wheat and testing the effects on yield is the first, but essential step, towards better understanding and possibly modifying cuticular wax composition. This will allow the production of more adaptable higher yielding wheat varieties.

The cuticle is the outermost layer of aerial plant organs and forms the interface between the plant and its environment. Cuticle composition is a vital determinant of a plant's physical properties, affecting water relations and light reflectance as well as interactions with fungal pathogens and insects. Despite its importance, we have limited understanding of the molecular mechanisms controlling its formation and composition. This has delayed progress towards understanding the costs and benefits of different cuticle compositions on plant yield and resource use efficiency. We have recently identified a wild emmer introgression that includes Iw1, a dominant glaucous inhibitor, which has a large effect on epicuticular wax morphology in wheat. This introgression has also been associated with consistent and significant increases in grain yield (average 4.15%) and extended grain fill in elite UK material under high yielding environments. The co-localization of these effects suggests that these multiple phenotypes are pleiotropic effects of Iw1. This challenges the long-held assumption that non-glaucousness is associated with reduced yield. In this proposal we will clone Iw1 to identify the molecular identity of this important gene. We will characterise cuticle and physiological properties of the Iw1 germplasm to understand its effect on plant performance and possible pleiotropic effects on yield and senescence. We will also examine the alternative hypothesis of linkage and not pleiotropy between these phenotypes. We have backcrossed this wild emmer segment into six UK varieties to validate these effects in multiple genetic backgrounds. The cloning of Iw1 will provide significant insights into the molecular mechanisms controlling cuticular wax deposition in wheat and provide an entry point to dissect this complex network in an important crop species. This should reveal strategies to optimize grain production under current and future UK growing conditions.

The most important potential impact of this research is the development and release of wheat varieties with improved yield and climate resilience based on a more comprehensive understanding of the molecular mechanisms underlying these traits. We expect several different beneficiaries of the proposed work, including the private sector in the form of wheat breeding companies, public sector policy makers, the UK environment and the wider public in general. Communications and Engagement Breeders and Industry: Cloning and characterizing Iw1 provides added value to breeders who currently use 'linked' markers and only the Shamrock allele. It will allow breeders to access allelic diversity in this gene and its homoeologues, provide more effective predictions on materials likely to benefit from this introgression and will decipher the exact role of Iw1 on yield and grain filling. We have shown before the importance of identifying and characterizing the underlying genes to advance our biological understanding of these processes and to develop new approaches for breeding. UK environment and society: The total UK wheat production in 2008 was 17 million tonnes and was valued at over £2.2 billion. This project will define a narrow genetic interval that has been shown to increase yield by an average 4.15% in an elite UK breeding line and in very high yielding environments. An increase in yield of just a quarter of this would increase production by 180 thousand tonnes with an estimated £23 million impact on the UK economy. In addition, understanding the effect of cuticle composition on yield and other parameters should inform on strategies to develop more climate resilient crops. This will directly benefit farmers by providing more stable yielding wheat varieties which in turn leads to better resource use efficiency as wastage is reduced. These benefits will have a broad impact in social well being and in the UK environment. Public sector policy makers: The research included in the proposal directly addresses the BBSRC priorities of 'Food Security' and 'Living with Environmental Change', thereby addressing policy makers' strategic goals. This research will inform policy makers of the importance and methodology of using biological diversity by providing a clear example of the potential benefits associated with using wild relatives for improvement of UK agriculture. Collaboration, Exploitation and Application To ensure quick delivery on this potential impact we have developed isogenic lines carrying this wild emmer introgression into six UK recommended varieties. To exploit this information we have established excellent links with the major UK wheat breeding companies who will provide important in kind contributions to this proposal. This comes as a consequence of the strong engagement between our group and breeders as they provide the conduit to channel our research into improved wheat varieties. Any material that is shown to have enhanced productivity in our proposal would be very close for public release. The isogenic and transgenic material plus the wild emmer BAC library developed in this proposal will allow new collaborations to be formed with plant biologist in other UK institutions. To convey the value and importance of this work to decision makers, the JIC is in constant conversation with local and national authorities to ensure that the outcomes of this and other research projects are effectively communicated. In summary, the strong collaboration with industry and our previous track record demonstrates that this research will be translated into commercial wheat varieties, ensuring that the potential impacts of this work are quickly transferred to society. Capability I strongly believe in the importance and mutual benefits that arise from interacting with the community. We will continue to pursue opportunities to engage with the community and establish more effective communication between scientists and society