The Secret Behind Bristle-Free Asian Rice? Human Selection.

The lack of awns in cultivated Asian rice has been linked to early agriculture and domestication by humans.

AsianScientist (Aug. 22, 2016) – An international research team has identified the genetic cause for the elongation of awns, the bristles that grow from grass ears, in rice. The study was recently reported in the Proceedings of the National Academy of Sciences.

During cultivation of wild cereals such as rice for human agricultural use, a number of domestication-related traits have been selected for over time. These include an upright growth habit, the ability of the plant to keep its seed when ripe rather than dispersing it, and a lack of awns.

Both Asian and African cultivated rice species share these traits, despite their geographical isolation from each other. This suggests the traits’ usefulness in promoting agriculture. However, the mechanism underlying awnlessness, in particular, was unclear.

Researchers at Nagoya University in Japan and their collaborators used a genetic mapping technique to identify a region on rice chromosome 8 that appeared responsible for awn elongation. They used a crossbreed between awnless African and Asian rice parents.

Methodical analysis of the region identified the RAE2 gene, which encodes a protein related to plant-specific peptides known to control plant development. The RAE2 peptide was shown to be functional in cultivated African rice, but dysfunctional in cultivated Asian rice.

A comparison of amino acid sequences between RAE2 and related peptides from other plants, including awned grasses, revealed six cysteine residues that allow the peptide to form a particular structure. However, the peptide present in awnless Asian rice lacked two cysteine residues.

“We compared the DNA sequence of RAE2 in different rice populations, and found a guanine-cystocine-rich region prone to genetic variation that encodes proteins with variable cysteine residues and, consequently, different lengths,” said first author Dr. Kanako Bessho-Uehara from the Nagoya University Bioscience and Biotechnology Center.

According to Bessho-Uehara, this variation disrupts the protein function and leads to awnlessness in Asian rice, but not African rice.

“Our findings show that the awn can be used to view the role of human selection in early agriculture and cereal domestication,” said Professor Motoyuki Ashikari of Nagoya University, a co-corresponding author on the study.

The article can be found at: Bessho-Uehara et al. (2016) Loss of Function at RAE2, a Previously Unidentified EPFL, is Required for Awnlessness in Cultivated Asian Rice.


Source: Nagoya University.
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