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Secret found to tripling grain number in sorghum

Discovery points toward strategy for significantly increasing yield of grain crops.

A simple genetic modification can triple the grain number of sorghum, a drought-tolerant plant that is an important source of food, animal feed and biofuels in many parts of the world.

In new research reported in Nature Communications, scientists at the Cold Spring Harbor Laboratory (CSHL) have figured out how that genetic change boosts the plant's yield. It does so by lowering the level of a key hormone, which then generates more flowers and more seeds.

Their discovery points toward a strategy for significantly increasing the yield of other grain crops, CSHL said.

Dr. Doreen Ware, a CSHL adjunct associate professor and research scientist with the U.S. Department of Agriculture's Agricultural Research Service (ARS), led the research, together with ARS colleague Dr. Zhanguo Xin. Their study focused on high-yield strains of sorghum that Xin generated several years ago.

According to the CSHL announcement, an unknown genetic mutation introduced by chemical mutagenesis — a method used for many decades by breeders and researchers to induce genetic variations in plants — resulted in an increase in the number of grains, i.e., seeds contained within fruits, that each plant produced.

Like many cereal crops, sorghum's grains are produced in clusters of flowers that develop from an elaborately branched structure at the top of the plant called a panicle. Each panicle can produce hundreds of flowers. There are two types of flowers, and usually only one of these — known as the sessile spikelet — is fertile. The other flower type — called pedicellate spikelets — does not make seeds.

In the modified plants Xin produced, however, both sessile spikelets and pedicellate spikelets produced seeds, tripling each plant's grain number, CSHL said.

Credit: Ware Lab, CSHL

Sorghum grains are produced in clusters of flowers that develop from an elaborately branched structure at the top of the plant called a panicle. Each panicle can produce hundreds of flowers. There are two types of flowers. In the plant one finds in the wild (left), only one of these, the sessile spikelet (SS), is fertile. The other type, pedicellate spikelets (PS), do not make seeds. In a modified version of the plant (right) both sessile and pedicellate spikelets produce seeds, tripling each plants grain number.

Ware and her team wanted to understand what caused this dramatic change. By completely sequencing the genomes of the modified plants, they found that the key mutations affected a gene that regulates hormone production. Plants carrying the mutation produce abnormally low levels of a development-regulating hormone called jasmonic acid, particularly during flower development.

Through subsequent experiments, the team learned that jasmonic acid prevents pedicellate spikelets from producing seeds.

"So, when the plant hormone is low, we get seeds set on every single one of the flowers, but when the plant hormone is high, we have a reduced number of fertile flowers, ending up in a reduced number of seeds," explained Dr. Yinping Jiao in Ware's lab and co-first author on the new paper.

Now that the team has uncovered the biological changes that triple sorghum's grain production, they hope to apply the same strategy to increase grain production in related plants that are vital in the global food supply, such as rice, corn and wheat.

The knowledge will help guide crop improvement through traditional breeding practices as well as approaches that take advantage of genome editing technologies, Ware said.

Founded in 1890, CSHL has shaped contemporary biomedical research and education with programs in cancer, neuroscience, plant biology and quantitative biology. The private, not-for-profit laboratory employs 1,100 people, including 600 scientists, students and technicians.

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