Researchers tweak corn to get more kernels

A laboratory in the United States used gene editing to increase crop yield per acre in both ear size and kernel number

In its former wild state, corn was a weedy plant with ears that contained maybe a dozen kernels. Today, an average ear of corn has about 800 kernels in 14 to18 neat rows. Some scientists want to improve on that.

At the Cold Spring Harbor Laboratory near New York City, professor David Jackson and postdoctoral fellow Lei Liu used CRISPR gene-editing technology to further increase the number of kernels per cob.

The corn genome is complex, and its DNA is divided into two parts: the gene and the regulatory regions that promote or suppress gene activity.

“A lot of people were using CRISPR in a very simple sense just to disrupt genes completely, to knock out the gene,” said Jackson in a news release. “But we came up with this new idea to CRISPR the promoter regions that turn the gene down, on. And that is what gives this very interesting result where we can get the variation in traits that we need in agriculture.”

The research was published in Nature Plants.

Corn yield is a function of harvested kernel number and kernel weight. The kernel number is set by ear size, which is influenced by the development of inflorescence meristems, a group of cells responsible for replenishing the stem cell pool. An inflorescence is a system of flower-bearing branches. Understanding how the meristem maintains its proper size is key to improving crop yields.

Jackson and Liu expect that their new CRISPR strategy will increase crop yield per acre in both ear size and kernel number, and help meet global food demands more sustainably.

“We looked at different varieties of corn and asked what the differences are between them and what explains why one variety may have better yields than another,” he said. “When researchers do those studies, they find that it’s not that different varieties have genes knocked out but it’s just a fine tuning. That is what accounts for the changes in productivity. It is natural evolution and natural variation. It’s not really a dramatic thing but small changes, tweaking.”

He said genetic mapping of the necessary traits were not well defined.

Jackson’s team used CRISPR to tinker with the corn genome promoter regions and modify stem cell growth. The pathway for kernel development includes genes that promote stem cell growth and differentiation into distinct plant organs.

Jackson’s team focused on a family of genes called CLEs that stops stem cell growth and plays vital roles in plant growth and development by promoting cell-to-cell communication.

“Corn has about 50 CLE genes with promoter regions that vary from gene to gene, and we are slowly trying to figure out what they are all doing,” said Jackson.

Jackson’s lab is one of the first to apply CRISPR to corn’s complex genome. He said his research team turned down selected genes to produce weak alleles that maintain normal ear shape but exhibit an increase in kernel rows.

“If you turn a gene off completely, the stem cells grow too much and become out of control, like a tumour. It makes the ears of corn look grotesque and the yield is low. What we did with CRISPR was turn the gene down.”

Disrupting the functions of CLE genes results in abnormal growth of ears that cannot be used in breeding. During the process of CRISPR gene editing to produce the weak alleles, the research team used data to help predict which gene promoter regions could be the most effective in manipulating the intended gene expression. The goal was that it would lead to an increase in kernel row number and grain yields without undermining other important agricultural traits.

Jackson said that this is the first step, a work in progress. He emphasized that the corn varieties used for the lab study are not the varieties grown commercially by farmers. Commercial varieties are all under commercial patents that cannot be genetically manipulated.

He is hoping that companies will pick up on the research and develop the CRISPR modifications into their brands. He added that there are so many things that affect crop yields, including climate change. A lot of people do not realize that there are thousands of crop varieties and breeders breed corn for local climate conditions.

“So, we basically randomly targeted the promoter region, but we have no idea which part of the promoter region is important,” said Liu in the news release.

“Probably the next step is that we will focus more on figuring out which part of the promoter is critical. And then, we will probably make our promoter CRISPR more efficient. We can get a better allele, which can produce more grain yield or ear size.”

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