From bread to beer — the gene mutation in barley

A research team led by Okayama University has discovered the gene mutation and enzyme that determine whether the dormancy of barley is long (better for food crops) or short (better for beer-making). Their results have been published in the journal Nature Communications.

Wild barley is characterised by long grain dormancy, which lasts for several months after grain maturation. This dormancy means that, initially, the grain will not germinate in response to transient moisture availability and will therefore survive hot, dry summers.

But while barley with long dormancy is ideal for the production of food crops, it is undesirable when malting barley kernels for brewing beer or distilling whisky, as seeds with long dormancy will by association require a long storage period prior to malting. Beverage producers are thus more inclined towards barley with short dormancy times.

Seeking to investigate the control of dormancy by the food and beverage industry, researchers from Okayama University, Japan’s National Institute of Agrobiological Sciences and the University of Adelaide compared DNA sequences of Haruna Nijo — a type of barley known to have short dormancy — with wild barley H602, known to have long dormancy. Haruna Nijo has a dominant short-dormancy allele called Qsd1, whereas H602 has a recessive long-dormancy allele called qsd1.

“The qsd1 gene for long dormancy appears to be a mutable gene that might be used for adaptation to different environments and this is consistent with the large variation in qsd1 sequence that exists in nature,” the researchers wrote.

“For example, the long dormancy qsd1 gene could be used to control pre-harvest sprouting in higher rainfall areas to enhance global adaptation of barley. On the other hand, certain haplotypes which carry the Qsd1 mutation are associated with barley lines that have been developed for industrial uses, such as in the malting and brewing industries.”

But what enabled the emergence of the Qsd1 mutation in the first place? After studying over 5000 plants, the researchers identified the section of the barley’s DNA that varies with expression of long or short dormancy — the gene AK372829.

AK372829 codes the enzyme alanine aminotransferase (AlaAT), which is known to play a pivotal role in nitrogen and carbon pathways and protein synthesis and has been implicated in stress responses to low oxygen and nitrogen availability. It has not, however, been linked with dormancy in plants — not until now, that is.

“We show that a single amino acid substitution in this enzyme reduces the dormancy period of mature barley grain,” the researchers wrote.

The researchers concluded that Haruna Nijo shares ancestry with long-dormancy, food-producing barley, suggesting “specific selection of reduced dormancy for the malting process”. They added that the selection and exploitation of plants expressing the Qsd1 mutation for short dormancy “contributes further to the debate as to what extent the development of ancient agrarian societies was driven by the human appetite for flour and bread, or for beer and alcohol”.

Image caption: The effects of qsd1 (left) and Qsd1 (right) alleles on seed germination after five weeks of 25°C dormancy reduction treatment.