Discovered gene essential for making ears of corn

by | May 17, 2019

A normal corn plant, left, and a barren stalk2 (ba2) plant, right. Plants with a mutation in the ba2 gene cannot grow ears, hence the name barren stalk. (Photo courtesy University of Missouri)

COLUMBIA, Mo. — A team of scientists led by University of Missouri maize geneticist Paula McSteen has identified a gene essential for forming the ears in corn.
The new research, which appears in the journal Molecular Plant, extends the growing biological understanding of how different parts of corn plants develop, which is important information for a crop that is a mainstay of the global food supply.
“Corn is a vitally important crop, and the ears are the most crucial organ for plant yield. Knowing the genes that control this process and how they function together at a molecular level is crucial for efforts to increase crop yield,” said McSteen, who is an associate professor of biological sciences in the College of Arts and Science and a principal investigator in Christopher S. Bond Life Sciences Center. “The information we glean from corn is also likely to be applicable to other cereals, including rice and wheat, because they also form grains on branches.”
The researchers found that a gene called barren stalk2, or ba2, affects development of axillary meristems, which are special cells that give rise to the ears.
As a corn plant grows, these cells are formed at nodes along the stalk.
These nodes look like tiny grooves, or indentations, in the stem. When the plant is ready to make ears, these cells begin to divide and bud out from the stalk.
These buds elongate to form the ear shoots and ultimately become the harvestable ears.
The process is initiated by delivery of a hormone, called auxin, to the nodes that signals the cells to make ears.
To find the genes needed to produce organs like ears or anything else, geneticists look for plants that cannot make the organ properly.
Plants with mutations in the ba2 gene never make ears, hence the name “barren stalk.”
The mutant plants do not have the grooves where the ears would form, which suggests that the gene functions early, before the ear bud forms.
The ba2 mutant was discovered in a large genetic screen for corn plants unable to make ears, and the gene was identified by molecular mapping to chromosome 2.
Previous screens like this identified a mutation in a different gene, called barren stalk1 or ba1,
that is also essential for making an ear. This other gene plays a key role in a molecular signaling pathway that controls ear development.
To test whether the newly identified barren stalk plants have a different problem, the researchers performed genetic crosses, known as a complementation test, and concluded that the phenotype they observed in their plant was caused by a mutation in a totally different gene.
“Interestingly, this is actually a lost-and-found case,” said McSteen. “We found that our mutation had previously been identified and characterized back in 1930, but had been lost sometime in the intervening years. It’s exciting to have been able to rediscover it and add it back to the stock.”

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