Comparative Grain Development in Temperate Grasses

Temperate or pooid cereal crops, such as wheat, barley and oat, represent a major world food source much of which is attributable to the storage capabilities of the cereal endosperm and influences of domestication selection. Brachypodium distachyon has recently become established as a genome-sequenced model system and the first wild member of the Pooideae be studied in detail. We provide the first detailed description of grain development in Brachypodium assessing its suitability as a model for grain development in crop species. Cellular and molecular mapping of developing Brachypodium endosperm domains reveals significant differences in aleurone differentiation reflecting differences in grain filling and endosperm storage reserves. We extend this survey of grain morphology and endosperm organisation to a wider sample of the Pooideae incorporating both wild and cultivated species. Focusing on the functionally important aleurone domains, distinct patterns of grain tissue organisation are described. Results indicate that organizational features are correlated to species’ ecological and grain quality characters and that the modified aleurone region, absent in Brachypodium, may be a feature of only a subset of cereals, specifically the Triticeae tribe. A more systematic candidate gene approach focusing on transcription factors was initiated in attempts to find the genes underpinning this variation. The identification of orthologous key regulatory genes with both similar and contrasting patterns of expression provides information on the differences and conservation of grain developmental pathways amongst the Pooideae. To investigate function of candidate genes, publically available insertional mutants for major MADS-box and YABBY genes were obtained and characterized, while simultaneously attempting to establish genetic transformation protocols to enable RNAi analyses of other candidate genes.