Characterization of the primary cell walls of seedlings of Brachypodium distachyon – A potential model plant for temperate grasses

Abstract

The genome of Brachypodium distachyon, also known as purple false brome, was fully sequenced in 2008 largely in response to the demand for a model plant for temperate grasses. A comparative study of the primary cell walls of seedlings of B. distachyon, Hordeum vulgare and Triticum aestivum was carried out. The cell walls of the three species were characterized by similar relative levels of, and developmental changes in, hemicelluloses. The occurrence of (1,3;1,4)-β- d-glucans was correlated with phases of growth involving cell elongation. Expression profiling of the genes involved in (1,3;1,4)-β- d-glucan synthesis ( cellulose synthase-like F family ( CSLF), CSLH and a putative synthase gene CSLJ) did not show a transcriptional regulation that corresponded to the abundance of (1,3;1,4)-β- d-glucans. CSLF6 transcripts were similarly highly expressed in all three grasses, and were much more abundant than any of the other transcripts. The CSLH transcript was relatively abundant in B. distachyon but almost undetectable in the other species. The deposition of arabinoxylans increased steadily during seedling growth in all three grasses, but they became less substituted and more cross-linked into the wall matrix during cell maturation. Moreover, arabinoxylans in B. distachyon differed from the two other grasses in having a lower degree of arabinose substitution, a higher percentage of ferulic acid in form of dimers and a larger proportion of ester-linked p-coumaric acid.