Abstract
Wheat is a major source of energy and nutrition worldwide, but it is also a primary cause of frequent diet-induced health issues, specifically celiac disease, for which the only effective therapy so far is strict dietary abstinence from gluten-containing grains. Wheat gluten proteins are grouped into two major categories: high-molecular-weight glutenin subunits (HMWgs), vital for mixing and baking properties, and gliadins plus low-molecular-weight glutenin subunits (LMWgs) that contain the overwhelming majority of celiac-causing epitopes. We put forth a hypothesis that eliminating gliadins and LMWgs while retaining HMWgs might allow the development of reduced-immunogenicity wheat genotypes relevant to most gluten-sensitive individuals. This hypothesis stems from the knowledge that the molecular structures and regulatory mechanisms of the genes encoding the two groups of gluten proteins are quite different, and blocking one group's transcription, without affecting the other's, is possible. The genes for gliadins and LMWgs have to be de-methylated by 5-methylcytosine DNA glycosylase/lyase (DEMETER) and an iron-sulfur (Fe-S) cluster biogenesis enzyme (DRE2) early during endosperm development to permit their transcription. In this study, a TILLING (Targeting Induced Local Lesions IN Genomes) approach was undertaken to identify mutations in the homoeologous DEMETER (DME) and DRE2 genes in common and durum wheat. Lines with mutations in these genes were obtained that displayed reduced content of immunogenic gluten proteins while retaining essential baking properties. Although our data at first glance suggest new possibilities for treating celiac disease and are therefore of medical and agronomical interest, it also shows that inducing mutations in the DME and DRE2 genes analyzed here affected pollen viability and germination. Hence there is a need to develop other approaches in the future to overcome this undesired effect.
Highlights
Wheat is the primary staple or source of energy to more than one-third of the world population [1, 2]
Other than the outlined benefits, wheat and derived products are the elicitors of several frequent diet-induced health issues, celiac disease (CD), wheat allergy, and nonceliac wheat sensitivity (NCWS), which collectively affect more than 7.5% of the US population [2, 8–10]
Seeds of the selected DRE2 TILLING mutants were obtained from the University of California, Davis, and seeds of the common wheat cultivar “Chinese Spring” nullisomic-tetrasomic lines lacking chromosome 5A, 5B, or 5D were obtained from the Wheat Genetics Resource Center (Kansas State University, Manhattan)
Summary
Wheat is the primary staple or source of energy to more than one-third of the world population [1, 2]. Carbohydrates (excluding non-starch polysaccharides), proteins, and dietary fibers like β-glucan and arabinoxylans, constitute 70–80%, 8– 14%, and 3.5–4.0% of the dry matter in wheat grain, respectively [3, 4]. Besides these macro-biomolecules, wheat serves as a source of a wide range of health-beneficial phytochemicals and minerals, such as vitamins B, E, and A, anti-oxidants phytosterols, phenolic acids, alkylresorcinols, lignans, choline, and betaine, and microelements Ca, Mg, Fe, Zn, and Cu [5–7]. There are 630 prolamin sequences identified; 351 of these sequences correspond to gliadins and 229 to glutenins [12]. An update to this database has been recently offered by Daly et al [13], which brought the number of curated common wheat prolamin sequences to 699 [13]
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