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Mentions: The outermost cell layer, or aleurone, is a functionally and structurally distinct but general feature of plant endosperm. The aleurone layer surrounds the central endosperm, except in the transfer cell region in temperate small grain cereals, and is composed of one (wheat) or more (barley) layers. The Brachypodium aleurone layer tends to be more irregular, being from one to three or more cells deep. It was noted that the Brachypodium aleurone layer appears to be structurally integrated with the central endosperm because it remains firmly attached to the endosperm during physical disruption of the grain (Fig. 3A). In wheat, the aleurone tends to adhere to the maternal tissues during disruption (Fig. 3B), a feature that is exploited during milling wheat grain and has the effect of separating the α-amylase activity in the aleurone from the starchy central endosperm.
Endosperm development in Brachypodium distachyon
Bottom Line: Development of Brachypodium grains is compared with that of wheat.The composition of these cell walls is more closely related to those of barley and oats than to those of wheat.Therefore, although endosperm development is broadly similar to that of temperate small grain cereals, there are significant differences that may reflect its phylogenetic position between the Triticeae and rice.
Affiliation: Department of Cell and Developmental Biology, John Innes Centre, Norwich NR4 7UH, UK.
Grain development and its evolution in grasses remains poorly understood, despite cereals being our most important source of food. The grain, for which many grass species have been domesticated, is a single-seeded fruit with prominent and persistent endosperm. Brachypodium distachyon, a small wild grass, is being posited as a new model system for the temperate small grain cereals, but little is known about its endosperm development and how this compares with that of the domesticated cereals. A cellular and molecular map of domains within the developing Brachypodium endosperm is constructed. This provides the first detailed description of grain development in Brachypodium for the reference strain, Bd21, that will be useful for future genetic and comparative studies. Development of Brachypodium grains is compared with that of wheat. Notably, the aleurone is not regionally differentiated as in wheat, suggesting that the modified aleurone region may be a feature of only a subset of cereals. Also, the central endosperm and the nucellar epidermis contain unusually prominent cell walls that may act as a storage material. The composition of these cell walls is more closely related to those of barley and oats than to those of wheat. Therefore, although endosperm development is broadly similar to that of temperate small grain cereals, there are significant differences that may reflect its phylogenetic position between the Triticeae and rice.
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