Location: Cereal Crops ResearchTitle: Comparative gene expression analysis of the beta-amylase and hordein gene families in the developing barley grain
Submitted to: Gene
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/14/2018
Publication Date: 4/20/2019
Citation: Vinje, M.A., Walling, J.G., Henson, C.A., Duke, S.H. 2019. Comparative gene expression analysis of the beta-amylase and hordein gene families in the developing barley grain. Gene. 693:127-136.
Interpretive Summary: Malt quality is an extremely complex agronomic trait that requires the coordination of numerous genes and their products in both the developing stages of barley as well as during controlled germination (i.e. malting). During barley development seed storage protein genes and starch-degrading genes are expressed and stored in the mature grain for use during germination or malting. Protein levels and starch-degrading levels are important in determining malt quality levels and they are significantly and positively correlated traits. Hordeins are the main contributors to protein levels and beta-amylase is one of the most important starch-degrading enzymes and both are expressed during barley grain development. However, stakeholders require low to moderate protein levels with high levels of starch-degrading power for use in the malting and brewing industries. The temporal expression of the major seed storage proteins, hordein, and one of the main contributors to starch degradation, beta-amylase, are not completely understood. Therefore, a comprehensive gene expression analysis was undertaken to document the temporal expression of hordeins and beta-amylase during barley grain development. Initiation of gene expression occurs during the pre-storage phase of barley grain development, which is earlier than previous known, in both hordeins and beta-amylase 1. Hordeins accumulate slightly earlier than beta-amylase 1 and is attributed to hordeins having more gene copies, whereas beta-amylase 1 is a single copy gene. Beta-amylase 2 is the main contributor to beta-amylase activity during the beginning to middle of grain development, whereas, beta-amylase 1 is the main contributor to beta-amylase activity during the middle to end of grain development. The impact of this research is twofold: 1) it eliminates expression time as a potential means of separating these two traits and 2) it directs future research to identify key genetic regulators that dictate gene expression during barley grain development.
Technical Abstract: Expression of hordeins and beta-amylase during barley grain development is important in determining malting quality parameters controlled by protein and malt enzyme levels. The relationship between protein and enzyme levels is confounding because, in general, protein and malt enzyme activity are significant and positively correlated and the malting and brewing industries demand relatively low levels of protein and relatively high levels of enzymes. Separation of these two traits is highly desired in the malting and brewing industry because high protein levels are a main cause of barley failing to meet malt quality. Gene expression studies on barley grain development have not resulted in a consensus on the temporal accumulation of hordein and beta-amylase transcript or protein. Therefore, the temporal expression patterns of hordeins (B- [Hor2], C- [Hor1], D- [Hor3], and gamma-hordein [Hor5]) were compared to endosperm-specific beta-amylase (Bmy1) throughout the entirety of grain development and determined to occur simultaneously with transcript accumulation beginning during the pre-storage phase of grain development. The largest increase in hordein and endosperm-specific beta-amylase transcript levels occurred between 5 and 9 (Hor2, Hor2-B1, Hor2-B3, Hor3, Hor5-gamma 1, and Hor5-gamma 3) or 9 and 13 days after anthesis (Hor1 and Bmy1). Additionally, ubiquitous beta-amylase (Bmy2) was determined to be the predominant beta-amylase present during early to mid-grain development whereas endosperm-specific beta-amylase was the predominant beta-amylase present during mid- to late grain development.