Redox-dependent interaction between thaumatin-like protein and β-glucan influences malting quality of barley

Abstract

Barley is the cornerstone of the malting and brewing industry. It is known that 250 quantitative trait loci (QTLs) of the grain are associated with 19 malting-quality phenotypes. However, only a few of the contributing genetic components have been identified. One of these, on chromosome 4H, contains a major malting QTL, QTL2, located near the telomeric region that accounts, respectively, for 28.9% and 37.6% of the variation in the β-glucan and extract fractions of malt. In the current study, we dissected the QTL2 region using an expressionand microsynteny-based approach. From a set of 22 expressed sequence tags expressed in seeds at the malting stage, we identified a candidate gene, TLP8 (thaumatin-like protein 8), which was differentially expressed and influenced malting quality. Transcript abundance and protein profiles of TLP8 were studied in different malt and feed varieties using quantitative PCR, immunoblotting, and enzyme-linked immunosorbent assay (ELISA). The experiments demonstrated that TLP8 binds to insoluble (1, 3, 1, 4)-β-D glucan in grain extracts, thereby facilitating the removal of this undesirable polysaccharide during malting. Further, the binding of TLP8 to β-glucan was dependent on redox. These findings represent a stride forward in our understanding of the malting process and provide a foundation for future improvements in the final beermaking process.Hordeum vulgare | malting | β-glucan | quantitative trait loci | thaumatin-like protein

Direct comparison of β-glucan content in wild and cultivated barley

“…The interaction has been found to be redox-dependent. [44] Since barley is mostly used in the brewing industry, during the breeding and genetic improvement process, the effect of genes which are coding for β-glucan synthesis could be automatically depleted. Due to low genetic influence for β-glucan synthesis, cultivated varieties may record a lower amount of β-glucan than wild barley accessions.…”

Impact on physiology and malting quality of barley exposed to heat, drought and their combination during different growth stages under controlled environment

“…The lowering of beta‐glucan levels in response to single and combined stress in variety Garnet is particularly interesting. It has been reported that stress‐induced thaumatin‐like proteins bind to beta‐glucans and facilitate their removal during malting (Singh et al ). It is tempting to speculate that an increase in protein levels in Garnet may be contributing to the lowering of the beta‐glucan levels in this variety.…”

Genome-Wide Exploration of Thaumatin-like Protein (TLP) Gene Family in Cereals

“…In Plants, TLPs are members of the PR-5 gene family that includes permatin, osmotin, osmotin-like proteins (OLPs), synthesis of which is mainly triggered in response to biotic and abiotic stress. However, it is also developmentally regulated during seed germination [1] and fruit ripening [2], which perform defense and development related functions 93 [3].…”

“…TLPs have roles in plant development and physiology, including tolerance to freezing stress [12] , antifungal activity [11], fruit ripening [13] and seed germination [14]. TLPs have been identified in various plants including Moss (Physcomitrella), Arabidopsis, Rice, Maize, Poplar and Barley [1,5,15].…”

“…Barley grain is typically used for malting purpose, and recently the role of TLPs has been shown in the germinating grains during the malting process [1]. Barley grain endosperm is composed of 75% nonstarch polysaccharides, such as (1, 3, 1, 4)-β-D glucan "(hereafter, β-glucan)" and arabinoxylans [16].…”