Newly developed tool reveals key mechanisms in major cereal, biofuel crop


Posted on July 23rd, 2019

Sorghum is one of the top five cereal crops in the world, and as academics have noted, a changing climate would make the plant even more important as a sustainable food and nutrition source. Sorghum is one of the single most efficient crops when it comes to water use and converting solar energy. 

Researchers at the HudsonAlpha Institute for Biotechnology contributed to a new reference genome for sweet sorghum in order to compare it to the reference genome for grain sorghum. This comparison can help scientists understand the genetic mechanisms that contribute to the different varieties having different strengths.

Grain Sorghum vs Sweet Sorghum

To understand the importance of comparing grain and sweet sorghum, you first need to understand the differences between the plants.

There are various types of grain sorghum, but as the name implies, they are all harvested for the grain they produce. That grain comes in red, orange, bronze, tan, cream, white, black and burgundy. Sorghum grain is commonly used in the food industry for products like flour. 

Sweet sorghum farmers, by contrast, care much more about the stalks of the plant than the grain. Sweet sorghum stalks are crushed to make a syrup, the same way producers crush sugarcane or beets. 

The difference in sugar storage distinguishes the two varieties, but the molecular reason the varieties function so differently is not well understood. With a new reference genome for sweet sorghum, scientists can compare the sequences for the two different varieties to understand the genetic mechanisms involved in sorghum sugar production and storage. In the long run, this knowledge could be used to breed sorghum varieties that are even more efficient in resource consumption and sugar production.

Finding Purpose

Throughout history, when people have newly domesticated crops, they typically do it in two steps. First, a wild species is cultivated by humans. Second, that domesticated species is then adapted to new environments and specialized uses. 

Sorghum has been developed to grow under a variety of water, solar and altitude conditions. The different varieties have also been selectively bred to increase various aspects of their production. Grain sorghum is bred for the quality of its grain. Biomass sorghum is bred for the quantity of biomass, which is used for biofuel. Sweet sorghum is bred for sugar accumulation in the stalks.

The breeding pressure that diversifies the crop leads to obvious differences between varieties. Exploring the genetic mechanisms that create those differences will help us better understand how to breed even more productive and versatile crops.

More Alike than Different

The comparison of the sweet and grain sorghum reference genomes showed that their genetic structure is largely the same. That stands out against crops like maize, where even closely related varieties show significant genetic differences. 

However, among the relatively few differences between the sweet and grain sorghum samples, scientists found changes in the plant’s sugar transport system. The research paper notes that the changes in sugar transport mechanisms could reveal the genetic pathways that lead to sugar remaining in the stalk, rather than moving to the seed.

By clueing in on the genetics of sugar storage, research could help guide breeding to produce an even more efficient sweet sorghum.

Crops of Tomorrow

A changing climate means changing demands for crops. Especially in parts of the world that rely more directly on subsistence farming, important food crops will need to be adapted in order to secure nutrition.

Sorghum also may prove essential as a biofuel crop. Understanding the mechanisms that help the plant efficiently store its sugars in its stalk will help in developing more productive varieties of the plant going forward.

These reference genomes reveal vast swathes of similarities between grain and sweet sorghum, but the few mechanisms that set the two apart could make all the difference.