Developing nutrient-enriched cereal grains with large embryos.

Cereal grains are composed of three main components: husk, starchy endosperm and germ. The germ (also called the embryo) accounts for only a small proportion of grain weight (2-3% in barley and wheat) but compared to the larger endosperm, it is rich in nutrients. Very often, cereal grains are processed to produce white flour which involves removing the husk and germ. However, whole grains are richer than white flour in fibre, nutrients, vitamins and minerals and there is an increasing public demand for products made from whole grains. This is because we now know that people who eat whole-grain foods have a lower risk of almost all chronic diseases. Our project aims to increase germ size, thus enhancing whole-grain quality for human health and animal nutrition. It is a partnership between cereal scientists at NIAB, Cambridge and at the James Hutton Institute (JHI) in Dundee.
Our project aims to identify the factors responsible for the reduction in relative germ size that has occurred during the domestication of cereals. It has been shown that endosperm size has increased during domestication in wheat, whilst germ size has remained constant. By comparing collections of wild and domesticated grains we hope to identify when and how relative germ size became sub-optimal during the course of domestication. Identification of the genetic factors responsible for this will provide the tools needed to allow rapid breeding for improved grain quality.
Studies of variants of cultivated barley and other cereals (rice and maize) have shown that it is possible to drastically increase germ size (although this is accompanied by a decrease in endosperm size). At present three genes have been discovered that control relative germ size. These are: GIANT EMBRYO (GE) in rice and maize, BIG EMBRYO 1 (BIGE1) in maize and PROLAMIN-BINDING FACTOR (PBF) in barley. We will investigate these genes and the genetic and biochemical pathways in which they work. Our aim is to find a way to increase relative germ size without causing deleterious decreases in endosperm size, grain size or yield.
Of the three genes known thus far to control germ size, PBF has the most commercial potential as it impacts on barley grain development only, without any detrimental effects on plant growth. However, the negative effect on endosperm size that accompanies reductions in PBF function is greater than that seen with GE and BIGE variants. To find a way to overcome this unfavourable impact on yield, first we will test whether it is possible to separate the favourable effects of PBF on the germ from the unfavourable effects on the endosperm using genetic manipulation. We will produce a barley plant with a functional PBF protein in the endosperm but lacking functional PBF in the germ. Secondly, we will investigate the mode of action of PBF to identify germ-specific and endosperm-specific target genes. Selecting for variation specifically in these target genes will allow plant breeders to optimize relative germ size.
Finally, we will build on our knowledge of the control of germ size in barley and other cereals to produce wheat with improved nutritional value. We will transfer the trait for optimal germ size to wheat by selecting for variation in the three genes known to control this in rice, barley and maize: GE, BIGE1 and PBF. We will use publicly-available germplasm resources in durum/pasta wheat and bread wheat to identify variant genes and then combine these together in different combinations. The resulting large-germ wheat will be assessed for improved grain quality. This approach provides a non-GM route to deliver wheat plants with enhanced nutritional quality.

In cereal grains, the embryo accounts for only a small proportion of grain weight but it is rich in nutrients. Increasing relative embryo size is known to enhance grain quality. We aim to uncover the impact of domestication on embryo size, provide information on the modes of action of three genes controlling embryo size and provide nutritionally-improved large-embryo wheat for human consumption.
It has been shown that relative embryo size has decreased during domestication in durum wheat. By comparing collections of wild and domesticated grains, and populations derived from crosses between these, we hope to identify when and how relative embryo size became sub-optimal during the course of domestication, and to identify the genomic regions responsible.
Studies of mutants, GIANT EMBRYO (GE) and BIG EMBRYO 1 (BIGE1) have shown that it is possible to drastically increase embryo size in rice and maize. In addition, we recently discovered in barley the first transcription factor, PROLAMIN-BINDING FACTOR (PBF) that regulates embryo size. Our aim is to increase relative embryo size without causing deleterious decreases in endosperm size, grain size or yield. To do this, we will 1) produce barley with a functional PBF protein in the endosperm but lacking functional PBF in the embryo; 2) investigate the genetic and biochemical pathways in which these genes work; and 3) identify embryo-specific target genes of PBF and manipulate the expression of these.
Finally, we will build on our knowledge of the control of embryo size in other cereals to produce wheat with improved nutritional value. We will select wheat TILLING mutants with variations in the orthologs of GE, BIGE1 and PBF. To optimize embryo size, we will combine the variant genes together in different combinations. The resulting large-embryo wheat will be assessed for improved grain quality. This approach provides a non-GM route to deliver wheat plants with enhanced nutritional quality.

The aim of this project is to expand our understanding of an important aspect of cereal grain quality, the control of embryo (germ) size and to exploit genes known to influence this trait as a means to improve grain quality in wheat and barley. This work targets the BBSRC strategic priority 'Food, nutrition and health'. It has been shown that people who eat whole-grain foods have a lower risk of almost all chronic diseases. This is because flour made from whole grains contains more fibre, nutrients, vitamins, minerals and beneficial phytochemicals than white flour. The embryo is a concentrated source of nutrients and work on large-embryo mutants of maize, rice and barley show the nutritional benefits of large-embryo grains for human food and animal feed. However, further refinements are required to reduce undesirable yield penalties associated with these mutations. The nutritional potential of large-embryo wheat remains to be explored. However, there is data to suggest that the process of domestication in wheat, with its associated increase in grain size, has inadvertently led to a decrease in relative embryo size and consequently, a decrease in grain quality. We will explore how this unfortunate side effect of wheat domestication can be reversed.
To provide a deeper understanding of embryo and endosperm development and how it is orchestrated, we will use existing mutants of barley with abnormally-large embryos to explore the molecular mechanisms that govern embryo-size determination. We will use our existing knowledge of these plants to test ways to maximize embryo size and nutritional value whilst minimizing deleterious decreases in yield. We will characterize the extent of variation in embryo size in existing wheat and barley germplasm, both ancestral and modern, and we will create new variants of wheat with enlarged embryos. Our data and germplasm, after appropriate protection of IP, will be released into the public domain and will be available to industrialists and academics worldwide.

Who might benefit from this research?
Plant breeders, farmers, food processors and manufacturers, consumers and plant scientists.

How might they benefit from this research?
Breeders will benefit from an increased understanding of how the relative sizes of the embryo and endosperm are established in cereal grain and how this affects grain quality. Our information on relative embryos sizes for modern cultivars and legacy accessions of wheat and barley, together with marker information on the genes responsible for this variation, can be used in breeding programmes to improve grain quality. Our work will provide germplasm that is not presently available i.e. cultivars of wheat and barley with large embryos and minimal yield penalty. These novel materials will provide breeding companies, farmers and end-users with new market opportunities for nutritionally-improved wheat and barley. In the longer term, therefore this work will enhance quality of life and health of consumers (thus reducing the societal and economic burden of chronic health disorders) by leading to nutritionally-improved wheat and barley for food and feed.
Plant scientists, both academic and commercial, will benefit from the barley gene expression data which will be of broad utility (not just limited to use within this project) and our analysis of transcription factor gene targets will provide a paradigm for other similar work. Also, further understanding of the control of relative organ size in plants has wider implications for efforts to improve non-cereal crop productivity and quality. The research community will also benefit from knowledge of the control of embryo size in wheat and barley and the genes that control this in order to achieve increases in grain quality in other cereal/plant species by similar means.