Description and functional analysis of the transcriptome from malting barley

Authors: Vinje, Marcus; Henson, Cynthia; DUKE, STANLEY - University Of Wisconsin; Simmons, Carl; LEE, KHOA - University Of Minnesota; HALL, EVAN - University Of Minnesota; HIRSCH, CORY - University Of Minnesota

Submitted to: Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/7/2021
Publication Date: 9/1/2021
Citation: Vinje, M.A., Henson, C.A., Duke, S.H., Simmons, C.H., Lee, K., Hall, E., Hirsch, C. 2021. Description and functional analysis of the transcriptome from malting barley. Genomics. 113(5):3310-3324. https://doi.org/10.1016/j.ygeno.2021.07.011.
DOI: https://doi.org/10.1016/j.ygeno.2021.07.011

Interpretive Summary: Malting and brewing share a common goal, which is to provide the nutrient solution that brewer's yeast uses to produce alcohol. Two of the major ingredients in malts that must be converted into smaller nutrients that yeast can adsorb are starch and protein. This conversion is the result of specific enzymes that are either present in the dry grain or are made by the grain during the malting process. This study investigated the specific genes that make the enzymes responsible for converting starch to small sugars and how these genes work together during the malting process. Unraveling these complex interactions revealed new enzymes and established the timing of how these genes integrate their actions to produce a high quality malt that is useful to brewers and distillers. Of particular interest is the discovery of a new enzyme which is in the category of enzymes thought to be most important in converting starch to small sugars that yeast use to produce alcohol. The impact of this work is that new opportunities to optimize grain quality and to improve the malting process have been discovered.

Technical Abstract: Barley malt is the primary ingredient used to brew beer. Simply explained, brewing beer is accomplished in three steps: malting, mashing, and fermentation. Malting is a form of controlled germination that occurs when raw barley is imbibed to ~45 % moisture, incubated at cool temperatures with rotation for 4-5 days, and kilned to stop the biological processes. During malting and mashing, large polymers (e.g. starch and protein) are converted into smaller polymers (e.g. maltose and amino acids) that are utilized by yeast during the fermentation process. However, a complete understanding of the genes and, most importantly, gene networks involved in the malting process have not been firmly established. Therefore, this work was undertaken to 1.) establish an early model of the malting transcriptome (i.e. The Maltome) that describes the expression of genes and their ontologies 2.) identify the period during malting with the largest dynamic shift in gene expression for future analysis and 3.) find all alpha-amylase, beta-amylase, alpha-glucosidase, and starch debranching genes in the barley genome and determine their expression patterns in the Maltome. Deep sequencing of the transcriptome on each day of malting was performed to identify as many differentially expressed genes as possible enabling us to report on an early model of the Maltome that describes the relevant changes in gene expression during malting. A search of the literature and barley genome identified 12 genes for alpha-amylase, beta-amylase, and alpha-glucosidase, one limit dextrinase gene and four isoamylase genes. Twenty-five of these starch degrading genes were differentially expressed in the Maltome including eleven alpha-amylase genes, six beeta-amylase genes, three alpha-glucosidase genes, and all starch debranching genes. A newly identified beta-amylase,Bmy3, was found to be highly expressed during malting and has great potential for relevance to the malting and brewing industry.