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

Lead Research Organisation: John Innes Centre
Department Name: Crop Genetics

Abstract

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.

Technical Summary

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.

Planned Impact

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 iluded 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
 
Description We developed a publicly-accessible BAC library of wild emmer wheat in collaboration with CNRGV in Toulouse, France.

We have fine mapped Iw1 to a sub-cM interval on chromosome 2BS and characterise the changes in wax composition conferred by this gene (Adamski et al Plant Journal 74:989).

We assembled a physical map across Iw1 and identified a small number of candidate genes. We have assessed one with negative results and are currently characterising additional genes.

We observed reduced recombination across this region due to the presence of a unique haplotype from wild emmer that does not allow recombination with modern wheat. We have generated a set of mapping populations to circumvent this. They are currently being characterised. We have also generated deletion lines across the Iw1 locus to further define the gene.

We identified consistent yield effects of Iw1 in one UK genetic background (~5% yield across three years) and have mapped the effect to a small interval including Iw1. However, this effect was not consistent in other genetic backgrounds suggesting that the yield effect might not be transferable across varieties.

The increased marker density has allowed us to develop a recombinant chromosome which includes both Iw1 and Sm1 (midge resistance) which previously could not be bred together since the alleles were in repulsion.

We have shown that Iw1 does not affect water use efficiency under UK environments and highlighted the importance of a more detailed characterisation of wax profiles in wheat genetic stocks differing in visual waxes.

We have validated the effect of the Iw1 interval on delayed senescence. We are conducting the final fine mapping of this effect which was consistent across six different UK varieties.

We have mapped the Wax producing gene (W1) and recently cloned this gene. We have also cloned the homologous cer-cqu genes in barley using the genetic knowledge of the Iw1/W1 region.
Exploitation Route We have developed more precise markers to incorporate Iw1 into breeding programmes. Importantly we have generated recombinant lines which carry both Iw1 and Sm1 (midge resistance) which is a major target of UK breeders.

We have shown that Iw1 increases yield in certain genetic backgrounds, but that this effect is not consistent across all germplas. This will allow breeders to deploy the gene in a more rationale manner.
Sectors Agriculture, Food and Drink

 
Description The information we have generated has informed breeders of the relative merits of this region in terms of yield and water use efficiency.
First Year Of Impact 2015
Sector Agriculture, Food and Drink
Impact Types Societal

 
Description UK Global Food Security Science Advisory Board
Geographic Reach Multiple continents/international 
Policy Influence Type Participation in a advisory committee
URL https://www.foodsecurity.ac.uk/
 
Title Wheat Training 
Description This website provides background information and practical resources to help both budding wheat scientists as well as researchers looking to expand their work into wheat. There is a need to improve crops to feed the world's growing population with the backdrop of climate change. Translation of fundamental plant biology research (e.g. from Arabidopsis thaliana) into crops such as wheat provides a potential route to deal with this challenge. However learning even simple tasks such as growing and crossing wheat plants requires time and effort, while material and methods sections in published articles are often short and cannot substitute teaching aids. This is also true for more complex topics such as the genomics aspect of wheat. 
Type Of Material Database/Collection of data 
Year Produced 2016 
Provided To Others? Yes  
Impact >4,500 sessions from >2,700 users 
URL http://www.wheat-training.com/
 
Description Bayer 
Organisation Bayer
Department Bayer CropScience Ltd
Country United Kingdom 
Sector Private 
PI Contribution Wheat genetics and genomics
Collaborator Contribution Wheat breeding and molecular knowledge
Impact joint projects
Start Year 2012
 
Description KWS 
Organisation KWS UK
Country United Kingdom 
Sector Private 
PI Contribution Genetics and genomics
Collaborator Contribution Breeder know how and germplasm
Impact joint projects
Start Year 2009
 
Description Limagrain 
Organisation Limagrain
Country France 
Sector Private 
PI Contribution Genetics and genomics
Collaborator Contribution Germplasm and breeder know-how
Impact Phd Studentship, field trails, among others
Start Year 2009
 
Description RAGT 
Organisation RAGT Seeds
Country United Kingdom 
Sector Learned Society 
PI Contribution Genetics and genomics
Collaborator Contribution Wheat germplasm and know how
Impact Shared projects
Start Year 2009
 
Description Discussion Norman Lamb, MP 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Policymakers/politicians
Results and Impact Discussion Norman Lamb, MP
Year(s) Of Engagement Activity 2017
 
Description Discussion with Gov Office Science 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Policymakers/politicians
Results and Impact Discussion with Gov Office Science
Year(s) Of Engagement Activity 2017
 
Description JIC Open day 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact JIC Open Day
Year(s) Of Engagement Activity 2018
 
Description • EPSO-EC Conference at EXPO Milano 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Policymakers/politicians
Results and Impact EU meeting on new breeding technologies
Year(s) Of Engagement Activity 2015