SAGE of the Developing Wheat Caryopsis

Understanding the development of the cereal caryopsis holds the future for metabolic engineering in the interests of enhancing global food production. We have developed a Serial Analysis of Gene Expression (SAGE) data platform to investigate the developing wheat (Triticum aestivum) caryopsis. LongSAGE libraries have been constructed at five time-points post-anthesis to coincide with key processes in caryopsis development. More than 90,000 LongSAGE tags have been sequenced generating 29,261 unique tag sequences across all five libraries. Tag abundance, generated from cumulative tag counts, provides insight into the redundancy and diversity of each library. Annotation of the 500 most abundant tags spanning development highlights the array of functional groups being expressed. The relative frequency of these more abundant transcripts allows quantitative analysis of patterns of expression during grain development. We have identified activities of cellular proliferation/differentiation, the accumulation of storage proteins and starch biosynthesis. The abundance of calcium-dependent protein kinases indicate their importance in signalling across development. Acquisition of a broad array of defence coincides with storage accumulation and is dominated by inhibitors of amylase activity. Differential expression profiles of abundant tags from each library reveal the coordinated expression of genes responsible for the cellular events constituting caryopsis development. This SAGE platform has also provided a resource of novel sequence and expression information including the identification of potentially useful promoter activities. Further investigations into both the abundant and low expressing transcripts will provide greater insight into wheat caryopsis development and assist in wheat improvement programmes.