The frequent classes of expressed genes in wheat endosperm tissue as possible sources of genetic markers

Frequently expressed genes in wheat endosperm tissue provide a potentially useful source of genetic markers because genes that are relatively highly expressed in seed development may provide new candidate genes contributing to quality traits in wheat. Wheat endosperm tissue at 8-12 days post anthesis (DPA) was characterised with respect to the accumulation of the major classes of seed storage proteins. The accumulation of these proteins characterises the wheat endosperm and provides a framework within which the frequencies of different expressed sequence tags (ESTs) could be categorised. Major seed storage protein classes such as glutenins and gliadins comprised approximately 40% of the proteins in 8-12 DPA endosperm tissue, and the levels of transcripts from the respective genes provided a benchmark for assessing the frequency of transcripts from other genes. Based on the analysis of 4374 sequences, 2 categories were defined: frequent class, comprising ESTs occurring at a frequency of >4 copies, and a second category containing ESTs occurring at a frequency of <3. Comparison of frequent class sequences of wheat with sequences from a corn library of an equivalent category identified genes apparently characteristic of wheat and others that were conserved during endosperm development. A significant new class of seed storage protein genes present in wheat but absent from corn, and related to avenin-3 of oats, was identified. Other prominent wheat ESTs, including a glycine-rich cell wall protein, End-1 (originally identified in early barley endosperm), Brittle-1 (corn, possible adenylate translocator), and an endosperm specific protein (EST expressed specifically in endosperm), were mapped in wheat using single nucleotide polymorphisms. The analysis demonstrated the feasibility of identifying new genes by large-scale sequencing and targetting these as possible markers for quality attributes.