A genome-wide analysis of 21 black rice varieties as well as red- and white-grained landraces demonstrated that black rice arose in a rice subspecies called tropical japonica (Japanese rice), one of the two independently domesticated Asian rice subspecies.
Black rice in Haikou, Hainan, China. Image credit: Anna Frodesiak.
Black rice has a rich cultural history. Called Emperor’s rice, it was amongst a number of foods that were set aside only for the Emperor in ancient China due to their quality or health benefits. No one else was allowed to eat these foods without approval from the Emperor.
In the time since, it remained popular in certain regions of China and recently has become prized worldwide for its high levels of antioxidants. Despite its long history, the origins of black rice have not been clear.
A new study, led by Dr Takeshi Izawa of Japan’s National Institute of Agrobiological Sciences, reveals the answer to the question of how black rice became black.
“The grain color of cereals is determined by the pigmentation of certain phytochemicals. In rice (Oryza sativa), most varieties have white grains, but some have brown, red, or black grains,” Dr Izawa and co-authors wrote in a paper published in the journal Plant Cell.
“The red grain color is due to the deposition and oxidative polymerization of proanthocyanidins in the pericarp.”
“The black grain color is caused by deposition of anthocyanins, but how these came to be made in the grains was not known.”
Dr Izawa and his colleagues from the National Institute of Agrobiological Sciences and the Forestry and Fisheries Research Center in Toyama, Japan, examined the genetic basis for the black color in rice grains.
The scientists discovered that the trait arose due to a rearrangement in a gene called Kala4, which activates the production of anthocyanins.
They concluded that this rearrangement must have originally occurred in the tropical japonica subspecies of rice and that the black rice trait was then transferred into other varieties, including those found today, by cross-breeding.
“The birth and spread of novel agronomical traits during crop domestication are complex events in plant evolution,” Dr Izawa said.
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Tetsuo Oikawa et al. The Birth of a Black Rice Gene and Its Local Spread by Introgression. Plant Cell, published online September 11, 2015; doi: 10.1105/tpc.15.00310
