The shoot and root growth of Brachypodium and its potential as a model for wheat and other cereal crops

The grass genetic model Brachypodium (Brachypodium distachyon (L.) Beauv., sequenced line Bd 21) was studied from germination to seed production to assess its potential as a phenotypic model for wheat (Triticum aestivum L.) and other cereal crops. Brachypodium and wheat shoot and root development and anatomy were highly similar. Main stem leaves and tillers (side shoots) emerged at the same time in both grasses in four temperature and light environments. Both developed primary and nodal axile roots at similar leaf stages with the same number and arrangement of vascular xylem tracheary elements (XTEs). Brachypodium, unlike wheat, had an elongated a mesocotyl above the seed and developed only one fine primary axile root from the base of the embryo, while wheat generally has three to five. Roots of both grasses could develop first, second and third order branches that emerged from phloem poles. Both developed up to two nodal axile roots from the coleoptile node at leaf 3, more than eight nodal axile roots from stem nodes after leaf 4, and most (97%) of the deepest roots at flowering were branches. In long days Brachypodium flowered 30 days after emergence, and root systems ceased descent 42 cm from the soil surface, such that mature roots can be studied readily in much smaller soil volumes than wheat. Brachypodium has the overwhelming advantage of a small size, fast life cycle and small genome, and is an excellent model to study cereal root system genetics and function, as well as genes for resource partitioning in whole plants.