Brachypodium distachyon grain: characterization of endosperm cell walls

Abstract

The wild grass Brachypodium distachyon has been proposed as an alternative model species for temperate cereals. The present paper reports on the characterization of B. distachyon grain, placing emphasis on endosperm cell walls. Brachypodium distachyon is notable for its high cell wall polysaccharide content that accounts for ∼52% (w/w) of the endosperm in comparison with 2-7% (w/w) in other cereals. Starch, the typical storage polysaccharide, is low [<10% (w/w)] in the endosperm where the main polysaccharide is (1-3) (1-4)-β-glucan [40% (w/w) of the endosperm], which in all likelihood plays a role as a storage compound. In addition to (1-3) (1-4)-β-glucan, endosperm cells contain cellulose and xylan in significant amounts. Interestingly, the ratio of ferulic acid to arabinoxylan is higher in B. distachyon grain than in other investigated cereals. Feruloylated arabinoxylan is mainly found in the middle lamella and cell junction zones of the storage endosperm, suggesting a potential role in cell-cell adhesion. The present results indicate that B. distachyon grains contain all the cell wall polysaccharides encountered in other cereal grains. Thus, due to its fully sequenced genome, its short life cycle, and the genetic tools available for mutagenesis/transformation, B. distachyon is a good model to investigate cell wall polysaccharide synthesis and function in cereal grains.

Loss of Cellulose Synthase-Like F6 Function Affects Mixed-Linkage Glucan Deposition, Cell Wall Mechanical Properties, and Defense Responses in Vegetative Tissues of Rice

“…The presence of large amounts of MLG in rice mature stems (after grain filling) is noteworthy, as most other studies in grasses have heavily focused on MLG analysis in coleoptiles, grains, or leaves (Carpita et al, 2001;Gibeaut et al, 2005;Doblin et al, 2009;Christensen et al, 2010;Guillon et al, 2011). Importantly, using electron microscopy, we were able to show that secondary cell walls of sclerenchyma fibers and xylem vessels of rice stems are heavily labeled with anti-MLG epitopes.…”

“…However, MLG also accumulates in cells that are not typically associated with growing tissues such as fibers and xylem vessels in the leaf (Trethewey and Harris, 2002;Doblin et al, 2009), which contain thick, lignified, secondary cell walls that provide structural and mechanical support. Another important role of MLG is as a storage compound particularly in barley (Hordeum vulgare), oats (Avena sativa), and Brachypodium distachyon grains where levels can represent as much as 70% to 80% of the endosperm cell wall (Fincher, 2009b;Guillon et al, 2011). In contrast to other cereals, rice does not accumulate significant amounts of MLG in the grain (Shibuya et al, 1985;Demirbas, 2005).…”

Tomato GDSL1 Is Required for Cutin Deposition in the Fruit Cuticle

“…Fruit exocarp (including cuticle) was collected from three independent 20-DPA fruits from wild-type and P35S-SlGDSL1 RNAi L-3 and L-17 lines and fixed as previously described (Guillon et al, 2011). Thin ultramicrotome sections (Microm RMC MT 700) of either 1 mm for confocal laser scanning microscopy or 100 nm for electron microscopy were obtained.…”

Brachypodium as a Model for the Grasses: Today and the Future

“…Therefore, for the vast majority of traits (e.g. cell wall composition, yield, stress tolerance, cell wall biosynthesis, root growth, development, and plant-pathogen interactions), Brachypodium can serve as a useful functional model for the grasses, and initial studies on cell walls, grain development, and root growth support Brachypodium's utility as a model system (Watt et al, 2009;Larré et al, 2010;Guillon et al, 2011;Opanowicz et al, 2011;Wang et al, 2011). f Assembly consists of sequenced BACs many of which contain unordered genes because of the difficulty associated with assembling repetitive DNA.…”