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Barley grain (1,3;1,4)-?-glucan content: effects of transcript and sequence variation in genes encoding the corresponding synthase and endohydrolase enzymes.

ABSTRACT: The composition of plant cell walls is important in determining cereal end uses. Unlike other widely consumed cereal grains barley is comparatively rich in (1,3;1,4)-?-glucan, a source of dietary fibre. Previous work showed Cellulose synthase-like genes synthesise (1,3;1,4)-?-glucan in several tissues. HvCslF6 encodes a grain (1,3;1,4)-?-glucan synthase, whereas the function of HvCslF9 is unknown. Here, the relationship between mRNA levels of HvCslF6, HvCslF9, HvGlbI (1,3;1,4)-?-glucan endohydrolase, and (1,3;1,4)-?-glucan content was studied in developing grains of four barley cultivars. HvCslF6 was differentially expressed during mid (8-15 DPA) and late (38 DPA) grain development stages while HvCslF9 transcript was only clearly detected at 8-10 DPA. A peak of HvGlbI expression was detected at 15 DPA. Differences in transcript abundance across the three genes could partially explain variation in grain (1,3;1,4)-?-glucan content in these genotypes. Remarkably narrow sequence variation was found within the HvCslF6 promoter and coding sequence and does not explain variation in (1,3;1,4)-?-glucan content. Our data emphasise the genotype-dependent accumulation of (1,3;1,4)-?-glucan during barley grain development and a role for the balance between hydrolysis and synthesis in determining (1,3;1,4)-?-glucan content, and suggests that other regulatory sequences or proteins are likely to be involved in this trait in developing grain.

SUBMITTER: Garcia-Gimenez G

PROVIDER: S-EPMC6872655 | biostudies-literature | 2019 Nov

REPOSITORIES: biostudies-literature

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Project description:Brachypodium distachyon is a small, fast growing grass species in the Pooideae subfamily that has become established as a model for other temperate cereals of agricultural significance, such as barley (Hordeum vulgare) and wheat (Triticum aestivum). The unusually high content in whole grains of ?-D-(1,3;1,4)-glucan or mixed linkage glucan (MLG), considered a valuable dietary fibre due to its increased solubility in water compared with cellulose, makes B. distachyon an attractive model for these polysaccharides. The carbohydrate composition of grain in B. distachyon is interesting not only in understanding the synthesis of MLG, but more broadly in the mechanism(s) of carbon partitioning in cereal grains. Several mutants in the major MLG synthase, cellulose synthase like (CSL) F6, were identified in a screen of a TILLING population that show a loss of function in vitro. Surprisingly, loss of cslf6 synthase capacity appears to have a severe impact on survival, growth, and development in B. distachyon in contrast to equivalent mutants in barley and rice. One mutant, A656T, which showed milder growth impacts in heterozygotes shows a 21% (w/w) reduction in average grain MLG and more than doubling of starch compared with wildtype. The endosperm architecture of grains with the A656T mutation is altered, with a reduction in wall thickness and increased deposition of starch in larger granules than typical of wildtype B. distachyon. Together these changes demonstrate an alteration in the carbon storage of cslf6 mutant grains in response to reduced MLG synthase capacity and a possible cross-regulation with starch synthesis which should be a focus in future work in composition of these grains. The consequences of these findings for the use of B. distachyon as a model species for understanding MLG synthesis, and more broadly the implications for improving the nutritional value of cereal grains through alteration of soluble dietary fibre content are discussed.

Dataset Information

Barley grain (1,3;1,4)-?-glucan content: effects of transcript and sequence variation in genes encoding the corresponding synthase and endohydrolase enzymes.

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