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.
