Evolution of rice linked to climate change

Researchers have linked the evolution of rice to abrupt climate change 4,200 years ago. The study suggests that a major global cooling event was the catalyst for the diversification and spread of rice into both northern and southern Asia.

Rice is a major food source for more than half of the global population. It was first cultivated in the Yangtze Valley in China 9,000 years ago, before spreading to the south and east. Eventually, rice migrated into the Middle East, Africa, Europe, and America. 

As it emerged in new regions, rice adapted to survive under different environmental conditions. Despite being such an important crop, there is much about the historical movement and evolution of rice that is unknown.

Led by experts at the NYU Center for Genomics and Systems Biology, researchers analyzed the genomes of more than 1,400 rice varieties to get a better understanding of its movement across Asia. The investigation was also based on geographical, archaeological, and climate data.

For the first 4,000 years of its history, rice was mostly limited to China, where the subspecies japonica was grown.

According to the new study, diversification of japonica rice coincided with a global cooling event 4,200 years ago. This extreme climate event has also been linked to the collapse of civilizations from Mesopotamia to China.

Temperate strains of rice emerged and migrated into northern China, Korea, and Japan, while tropical varieties migrated into Southeast Asia.

“This abrupt climate change forced plants, including crops, to adapt,” said study lead author Rafal M. Gutaker. “Our genomic data, as well as paleoclimate modeling by our collaborators, show that the cooling event occurred at the same time as the rise of temperate japonica, which grows in milder regions.” 

“This cooling event also may have led to the migration of rice agriculture and farmer communities into Southeast Asia.”

Professor Michael D. Purugganan explained that these findings were confirmed by the analysis of archaeological rice remains excavated in Asia.

The data also showed that after the cooling event, tropical rice migrated south and temperate rice adapted to northern latitudes.

Tropical varieties of japonica rice continued to diversify and appeared in the islands of Southeast Asia about 2,500 years ago. The archeological data indicated that this movement was facilitated by extensive trade networks.

The spread of indica rice, a subspecies that originated in India about 4,000 years ago, was found to be more complex. The researchers traced its migration from India into China around 2,000 years ago.

The experts found that temperatures had the biggest environmental influence on rice diversity. The study revealed that heat accumulation was strongly linked to the genetic differences between tropical and temperate rice.

A better understanding of rice migration could help scientists develop new varieties that can endure the extreme conditions associated with climate change. 

“Armed with knowledge of the pattern of rice dispersal and environmental factors that influenced its migration, we can examine the evolutionary adaptations of rice as it spread to new environments, which could allow us to identify traits and genes to help future breeding efforts,” said Gutaker.

The study is published in the journal Nature Plants.

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By Chrissy Sexton, Earth.com Staff Writer