Food and nutrition security requires safe access to affordable and nutritious food supplies. Work Package 2 aims to enhance grain quality for human health, combat non-communicable diet-related diseases and improve the resilience of wheat production systems to biotic stresses. It addresses two topics, with shared objectives across Designing Future Wheat and other Rothamsted Research, John Innes Centre, Earlham Institute, Quadram Institute and National Institute of Agricultural Botany programmes. Both exploit previous BBSRC investments in germplasm resources and the latest genomic developments, to understand and manipulate the genes and pathways defining wheat grain composition and host resistance or susceptibility to pathogens or pests.
Dietary fibre and resistant starch are generally accepted as beneficial for human health. We plan to manipulate their amount, composition and properties, by dissecting the genetic and biochemical mechanisms determining their beneficial properties in material produced by the exploitation of natural and induced genetic variation. This will allow us to work with breeders and food processors to develop wheat products with improved quality for human health. Wheat is also an important source of the essential micronutrients iron and zinc. Many diets are deficient in micronutrients, (iron in the UK) and both elements worldwide. We aim to increase the amount and bioavailability of these essential micronutrients in wheat grain.
Wheat products such as bread, pasta and biscuits are a major source of dietary carbohydrates, mainly in the form of starch. Starch properties, such as amylose:amylopectin ratio and the proportion of A/B-type granules, influence starch functionality and digestibility. There is increasing evidence of health benefits from starches resistant to digestion, however resistant starch levels remain very low in wheat foods. The exome-sequenced Cadenza mutant population will be used to systematically generate and characterise a panel of wheat lines with various combinations of mutations in starch biosynthesis genes anticipated to affect starch structure, composition and digestibility. An available high-amylose mutant will be used to characterise modifier genes and lines with altered A/B-type granule composition to investigate their influence on starch functionality. These studies will provide the understanding and tools required to breed wheat varieties with improved starch quality and diverse functionality.
- Novel wheat starch panel with unique combinations of mutations and characterised starch phenotypes available for wheat quality, agronomic and human health trials.
- Identified and characterised genetic modifiers of amylose content and tools for their transfer to elite UK varieties.
- Understanding of the influence of starch granule size on grain nutritional properties and of the stability of these properties to environmental change in lines lacking B-type granules.
Dietary fibre is severely deficient in the UK diet, with adults consuming on average about half their recommended daily intake. This is of concern because dietary fibre, particularly cereal, reduces the risk of a range of chronic diseases, including cardiovascular disease, type 2 diabetes and certain types of cancer (notably colorectal). These effects are not fully understood but several mechanisms are thought to contribute, including reduced rate of duodenal digestion, decreased intestinal transit time, increased binding of cholesterol and carcinogens and increased colon fermentation (increasing short fatty acid levels such as butyrate which is beneficial for colonocytes).
Bread is a significant source of UK dietary fibre, accounting for about 20% of daily adult intake. White bread accounts for about half of this, and about 80% of total consumption. Although white bread fibre content (~2-3%) is lower than that of wholemeal (~11-15%), a higher proportion is soluble, which may have some advantages. The programme aims to increase the amount of total and soluble dietary fibre in white flour, particularly arabinoxylan, which accounts for about 70% of total fibre. Beta-glucan accounts for about 20% of total fibre in wheat, but has higher solubility and viscosity than in barley and oats, where it is known to have beneficial effects on serum cholesterol. The programme aims to explore the content and understand the properties of beta-glucan in wheat, aiming to increase both total and soluble forms.
Finally, fructans (fructooligosaccharides) account for about 2-3% of whole grain dry weight and being rapidly fermented to short chain fatty acids (SCFA) in the colon, are beneficial to most consumers. However, fermentation of fructans may also produce gas, which causes discomfort to a significant proportion of irritable bowel syndrome sufferers. The programme will therefore seek sources of both high and low levels of fructans in whole wheat grain and white flour
Iron and zinc are essential for human health, with deficiencies estimated to affect about 40% and 33% respectively of the world population. Although zinc deficiency does not generally affect the UK population, iron deficiency anaemia is the most widespread form of anaemia, affecting about 6% of women of child-bearing age. Cereals are significant sources of both elements, and white bread is fortified with iron to the levels in wholemeal. However, there are concerns about the bioavailability of the forms of iron used, and they may be harmful for some individuals due to the formation of iron sulphides in the colon.
The endogenous forms of both elements in wheat also have low bioavailability because they are largely located in the aleurone layer and embryo where they are bound to phytic acid to give insoluble phytates. Hence, the programme will not only identify variation in the partitioning of iron and zinc to and within the grain, but will also determine their pathways and mechanisms of transport within the developing grain as a basis for developing strategies to increase their accumulation in bioavailable forms within the starchy endosperm.
- Characterised sources of natural variation for high iron and zinc plant uptake and in partitioning in whole grain and white flour, and major QTL for accumulation mapped.
- Pathway of transport of iron and zinc from transfer cells to aleurone layer (iron), and embryo (zinc) identified in developing caryopses.
- Identification of transporters and genes associated with iron and zinc trafficking in the grain.
Wheat suffers from devastating epidemics/pandemics due to diseases and pests affecting yield and quality; requiring costly methods of control. Pathogens and pests manipulate host metabolism to enable successful colonisation. However, plants are capable of withstanding diverse pathogens and pests through the action of broad spectrum and more specialist resistance genes. The diversity, evolution and mechanism of action of these different resistance genes will be studied to achieve a more durable and broader spectrum of plant defence.
The infection biology of key pathogens, communication events and molecular processes targeted in successful colonisation will be investigated, focussing on rusts, Zymoseptoria, Fusarium, take-all, eyespot, and two aphid species, the bird cherry-oat aphid (Rhopalosiphum padi) and the English grain aphid (Sitobion avenae). These are the major biotic threats to high yielding UK-European wheat cropping systems, and also contribute repeatedly to significant global problems. Grain yield losses per threat are typically in the range 10 to 25%, even when fully integrated control options have been correctly applied. In some cases, these biotic threats are currently intractable to the breeding community.
We aim to understand different types of host resistance and how they can be combined to achieve durable and broad-spectrum resistance. We will exploit the rich diversity present in the Watkins landraces, synthetic hexaploid wheats (SHW) and the ancestral wheat relative donors and amphidiploids, which have become amenable to genetic analysis through the WISP wheat pre-breeding programme. Parents and mapping populations of these germplasm collections will be screened for reduced susceptibility to Zymoseptoria isolates, scored as differences in the duration of the latent (symptomless) phase of infection. Similarly, germplasm resistance to take-all, Fusarium, eyespot, the bird cherry-oat aphid and the English grain aphid will be assessed under field and controlled environment/laboratory conditions. Germplasm with Fusarium resistance will be assessed for resistance to mycoxtoxin deoxynivalenol (DON) accumulation in grain.
- Characterised diversity panels and historical wheat precise genetic stocks in UK winter wheat adapted backgrounds for a diverse set of pathogens and pests.
- New markers, genes and alleles (natural and induced) to enhance plant resistance.
- QTL/genes/alleles minimising trade-off with resistance to other pathogens (biotrophic, hemi-biotrophic and necrotrophic).
- Lines with broad-spectrum and durable disease resistance through optimal gene combinations.
- Modified host susceptibility targets hijacked by pathogens and pests.
- Minimised initial pathogen and pest population establishment on the host.
We aim to investigate the core and variable mechanisms implicated in virulence/ avirulence, and the infection biology of wheat pathogenic fungi and cereal aphids. This will include studies on their evolution, feeding behaviour, interactions with host targets, and in the case of the Take-all fungus, their interactions with other components of associated wheat rhizosphere/endosphere microbial communities.
The approaches we will use range from field scale analysis through to detailed single cell procedures, all underpinned by robust bioassays and molecular gene functional analyses. Whole tissue and single cell ‘omics experiments will be performed to elucidate the regulatory mechanisms by which pathogenic fungi and aphids infect/ colonise wheat tissues. The full range of secreted candidate virulence factors (metabolites, proteins, RNAs) will be predicted via transcriptomic analyses, and functionally characterised through genetics, bioimaging and biochemistry. Combining fungal mutagenesis and NGS re-sequencing approaches, the key fungal genes/processes required for ‘core’ (all interactions) and ‘specific’ (isolate x cultivar) disease establishment on wheat will be elucidated, as well as those essential for pathogen fitness (viability). Target genes will be validated by reverse genetics and complementation approaches.
Advances in technology facilitate adoption of new ways of working with wheat. WP2 aims to complement traditional approaches with modern practices, expediting the discovery, exploitation and translation into commercial varieties and fully integrating control strategies. Coordinating with WP3, conditions for accelerated generation advancement of wheat and its progenitor species will be established and refined. Protocols for scoring adult plant disease phenotypes under accelerated growth conditions will be developed. Work with WP1 and WP4 will expand robotic phenotyping and image analysis to supplement traditional visual field inspection with image based phenotyping of wheat pathogens and pests.
Technologies will be extended into improved growth-chamber based pathology/ pest assessment, microscopy and phenotyping, with molecular signatures of resistance and susceptibility to better understand pathogen and pest progression during infection.