De novo expression of beta-amylase2 (Bmy2) in barley grains during micromalting

Authors: Vinje, Marcus; DUKE, STANLEY - University Of Wisconsin; Henson, Cynthia

Submitted to: Journal of the American Society of Brewing Chemists
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/12/2019
Publication Date: 1/28/2020
Citation: Vinje, M.A., Duke, S.H., Henson, C.A. 2020. De novo expression of beta-amylase2 (Bmy2) in barley grains during micromalting. Journal of the American Society of Brewing Chemists. 78(2):126-135. https://doi.org/10.1080/03610470.2019.1705104.
DOI: https://doi.org/10.1080/03610470.2019.1705104

Interpretive Summary: Beta-amylase is an important enzyme to the malting and brewing industry because it is the main driver of diastatic power, one of the most important malting quality traits. In barley, there are two functional beta-amylases encoded by the Bmy1 and Bmy2 genes (Bmy1 and Bmy2, respectively). In order to make beer, barley first must be malted, which is a controlled germination, followed by mashing. Mashing is the process of mixing ground malt with hot water to break down large molecules such as protein and starch into their smaller subunits like amino acids and sugars. The high temperatures involved in mashing can inactivate Bmy1. Both Bmy1 and Bmy2 are found in the mature grain but Bmy1 is the predominant beta-amylase, whereas Bmy2 is not found at useful levels. Interestingly, Bmy2 is the more thermostable beta-amylase. Expression of beta-amylase is not thought to occur in barley during malting but, notably, expression of Bmy2 is seen in wheat and rye during germination. Therefore, this research was conducted to determine if barley Bmy2 is expressed during micromalting. High levels of Bmy2 gene expression is observed during micromalting in both a two- and six-row malting cultivar (Conrad and Legacy, respectively). Legacy Bmy2 transcript levels increased 40-f0ld and Conrad Bmy2 transcript levels increased 20-fold during micromalting. Legacy had significantly (1.9-fold) more Bmy2 transcript levels than Conrad by the end of micromalting. Beta-amylase activity and Bmy2 protein levels corroborated the gene expression data thus reliably demonstrating for the first time the expression and accumulation of a beta-amylase (Bmy2) during micromalting. This knowledge will lead to further exploration of cultivated and wild barleys to identify lines with high Bmy2 expression during micromalting.

Technical Abstract: Beta-amylase is important to the malting and brewing industry because it is one of four main enzymes involved in fermentable sugar production during mashing. There are two functional barley beta-amylases encoded by the Bmy1 and Bmy2 genes. Mashing is commonly performed at high temperatures and beta-amylase1 (Bmy1) is vulnerable to thermal inactivation at these temperatures. Unlike Bmy1, Bmy2 is not stored at useful levels in the mature grain but Bmy2 encodes a more thermostable beta-amylase. Expression of beta-amylase is not thought to occur during malting but, interestingly, de novo expression of Bmy2 is seen in other Triticeae tribe members during germination. Therefore, this research was conducted to determine if barley Bmy2 is de novo expressed during micromalting. De novo expression of Bmy2 is observed in both a two- and six-row malting cultivar (Conrad and Legacy, respectively). Legacy Bmy2 transcript levels significantly increased (40-f0ld) between 0 and 4 Days of Germination (DoG) and Conrad Bmy2 transcript levels significantly increased (20-fold) between 0 and 3 DoG. Legacy had significantly (1.9-fold) more Bmy2 transcript levels than Conrad by the end of micromalting. Beta-amylase activity and protein immunoblots corroborated the gene expression data thus reliably demonstrating the de novo expression of Bmy2 during micromalting.