Tiny plant, big deal

The chickpea, also known as the garbanzo bean, is the world’s second-most widely grown legume crop after the soybean, making it a major component of the world’s diet. It is an important crop especially for small-farm operators in Asia and sub-Saharan Africa. An international team of 49 scientists from 23 organizations in 10 countries have been able to sequence the genes of this notable food supply.

The chickpea plant is a type of legume, making it very different from other agricultural crops.

“[Chickpeas] can be grown on poor soils worldwide, without application of nitrogen fertilizer,” said Alison Berry, a professor of plant sciences at UC Davis. “This is because legumes are hosts for beneficial bacteria that live inside the roots, in symbiotic structures called root nodules. These bacteria directly provide the plants with nitrogen through the enzymatic process of nitrogen fixation.”

Fixing nitrogen refers to the plant’s ability to draw nitrogen out of the atmosphere and incorporate it into its cellular structure. The ability of this plant to fix nitrogen also makes this crop especially nutritious for humans.

“Crop legumes, like chickpeas, soybeans, peanuts, etc. are major dietary staples for millions of people globally, in large measure because the seeds are very high in protein as a result of the nitrogen fixation process,” Berry said.

The chickpea contains an estimated 28,269 genes. It was sequenced randomly and then put back together using the overlapping regions. The 28,000 genes contain nearly 750 million base pairs. These pairs were taken apart and put back together 100 at a time. Each group of 100 base pairs overlaps slightly with the next set, allowing them to be reassembled like a puzzle.

Since there are 7.5 million sets of 100, the reassembly was carried out by a computer algorithm, since doing it by hand would take hundreds of years.

“The assembly ‘problem’ is actually quite significant, because large genomes such as chickpeas contain many repeated sequence motifs, comprising about 50 percent of the genome, and these motifs complicate assembly,” said Douglas Cook, a UC Davis professor of plant pathology and a lead author on the research paper. “In the case of chickpeas, only about 75 percent of the genome could be assembled.”

With this discovery, scientists have been able to start separating the information and matching genes with traits in the species. This makes selective breeding easier for scientists, like Paul Gepts, at UC Davis. Gepts has been working with garbanzo beans in his lab where he is responsible for producing new varieties of lima beans, garbanzo beans and common beans.

“The sequencing of the genome will make the process of selective breeding more efficient,” Gepts said.

This means scientist now can better understand how to improve the species and promote the maximum crop yield.

“In the case of legumes, like chickpeas, we can apply genomic knowledge for the improvement of crop traits — drought tolerance, resistance to disease, increased yields in poor soils — that can be of benefit,” Berry said. “In addition, it may eventually be possible to understand how legumes manage to form nitrogen-fixing associations with bacteria. Maybe this trait, or some parts of it, can be transferred to other crops.”

In the future, this can lead to a great number of improvements for the species and understanding how to apply this strategy to other crops.

According to Berry, a sequenced genome is like a treasure chest of future discoveries. The precise information about every gene of an organism can open doors to understanding fundamental questions about life.

KELLY MITCHELL can be reached at science@theaggie.org.

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