Dataset Information

Structural organization and functional divergence of high isoelectric point α-amylase genes in bread wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.).

ABSTRACT:

Background

High isoelectric point α-amylase genes (Amy1) play major roles during cereal seed germination, and are associated with unacceptable high residual α-amylase activities in ripe wheat grains. However, in wheat and barley, due to extremely high homology of duplicated copies, and large and complex genome background, the knowledge on this multigene family is limited.

Results

In the present work, we identified a total of 41 Amy1 genes among 13 investigated grasses. By using genomic resources and experimental validation, the exact copy numbers and chromosomal locations in wheat and barley were determined. Phylogenetic and syntenic analyses revealed tandem gene duplication and chromosomal rearrangement leading to separation of Amy1 into two distinct loci, Amy1θ and Amy1λ. The divergence of Amy1λ from Amy1θ was driven by adaptive selection pressures performed on two amino acids, Arg₉₇ and Asn₂₃₃ (P > 0.95*). The predicted protein structural alteration caused by substitution of Asp₂₃₃Asn in the conserved starch binding surface site, and significantly expressional differentiation during seed germination and grain development provided evidence of functional divergence between Amy1θ and Amy1λ genes. We screened out candidate copies (TaAmy1-A1/A2 and TaAmy1-D1) associated with high residual α-amylase activities in ripe grains. Furthermore, we proposed an evolutionary model for expansion dynamics of Amy1 genes.

Conclusions

Our study provides comprehensive analyses of the Amy1 multigene family, and defines the fixation of two spatially structural Amy1 loci in wheat and barley. Potential functional divergence between them is reflected by their sequence features and expressional patterns, and driven by gene duplication, chromosome rearrangement and natural selections during gene family evolution. Furthermore, the discrimination of differentially effective copies during seed germination and/or grain development will provide guidance to manipulation of α-amylase activity in wheat and barley breeding for better yield and processing properties.

SUBMITTER: Ju L

PROVIDER: S-EPMC6404323 | biostudies-literature |

REPOSITORIES: biostudies-literature

ACCESS DATA

Similar Datasets

Project description:The food enzyme considered in this opinion is a 4-?-d-glucan maltohydrolase (EC 3.2.1.2) obtained from grain of barley (Hordeum vulgare), by the companies Genencor International B.V. and Senson Oy. This ?-amylase is intended to be used in several food-manufacturing processes: baking and brewing processes, distilled alcohol production, and starch processing for the production of glucose syrups. The compositional data provided for the food enzyme were considered sufficient. The manufacturing process did not raise safety concerns. Based on the maximum use levels recommended for the respective food processes, dietary exposure to the food enzyme-total organic solids (TOS) was estimated on the basis of individual data from the EFSA Comprehensive European Food Consumption Database. This exposure estimate is similar to or lower than the exposure to a fraction of barley comparable to the food enzyme-TOS, resulting from the consumption of barley-derived foods. As the food enzyme is derived from edible parts of barley, in line with the requirements of the guidance document on food enzyme assessment, the Panel accepted that there was no need for the provision of toxicological data for this food enzyme and the Panel concluded that this food enzyme does not give rise to safety concerns under the intended conditions of use. Considering the potential for allergenicity, the gluten content of the food enzyme was below the detection limit of the analytical method, which is well below the level of 20 mg/kg for 'gluten-free' products. The amino acid sequence of the ?-amylase was compared to those of known allergens and no match was found. The food enzyme ?-amylase from barley is an occupational respiratory allergen and may contain low levels of other allergenic barley proteins that may trigger adverse reactions upon oral challenges in individuals with an oral sensitisation to cereals. The Panel considers that dietary exposure to the food enzyme ?-amylase from barley may result in incidental cases of food allergic reactions.