Identifying the genetic basis of large-embryo mutants of barley affected at the Lys3 locus

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Grain quality in cereals is determined by the composition and relative sizes of the three main components of the grain: the endosperm, embryo (or germ) and the husk. The endosperm is starch-rich and it provides the bulk of dietary calories. In contrast, the embryo accounts for a small proportion of grain weight but it is nutrient-rich. The embryo contains several essential nutrients that are lacking or less abundant in the other grain components. In barley, we have shown that a locus, Lys3 that controls grain lysine content also controls embryo size. Barley mutants affected at the Lys3 locus have embryos that are approximately twice the mass of normal embryos. As with the giant embryo mutants of maize, lys3 mutants of barley have also shown improved nutritional value as animal feed. Unfortunately, their uptake has been limited by reduced grain yield caused by reduced endosperm size and therefore low grain weight. In addition to the effects of lys3 mutations on grain quality and organ size, we recently discovered an unexpected side-effect on the efficiency of barley transformation. One of the lys3 mutants consistently gives transformation efficiencies equivalent to those of Golden Promise. To understand the biological basis of the control of embryo size in barley and in the long term, to manipulate this most effectively and efficiently in cereal species generally, we need to identify the Lys3 gene. To do this, we propose to fine map the region of the barley genome containing Lys3. In addition we aim to transfer a lys3 mutant allele to elite barley cultivars thus generating tools for future barley improvement by genetic engineering.

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