The high quality genome sequence of the dry jujube cultivar ‘Junzao,’ along with sequences from trees throughout its range, have illuminated the domestication history of this popular Asian fruit tree.
‘Junzao’ jujube in Xinjiang, China. Image credit: Xingang Li.
The Chinese jujube (Ziziphus jujuba) is one of the oldest cultivated fruit trees, with more than 7,000 years of domestication history.
It is native to China and belongs to the Rhamnaceae family in the Rosales order.
Jujube is valued as a woody crop and traditional herbal medicine, and cultivated on 2 million hectares in China alone, with an annual production of approximately 4.32 million tons.
Jujube cultivars have been traditionally classified as fresh or dry, and dry jujubes account for approximately 80% of the total production. Ripe fruits of dry jujube have a coarse texture while those of fresh types have a crisp texture.
An international team of researchers from Northwest A&F University, Novogene Bioinformatics Institute, Cornell University’s Boyce Thompson Institute, Beijing Forestry University and Kunming Institute of Botany sequenced the dry jujube, as well as 31 cultivated and wild varieties, to gain insight into its domestication process.
The genome sequences showed that cultivated jujube plants interbred with wild varieties several times during its history of human cultivation.
Comparative analysis of the genomes also revealed that a type of jujube that is eaten fresh and has a crisper texture, called Dongzao, has a recent insertion into its genome that the Junzao variety does not have.
“Comparative analysis revealed that the genome of ‘Dongzao’, a fresh jujube, was 86.5 Mb larger than that of the ‘Junzao’, partially due to the recent insertions of transposable elements in the ‘Dongzao’ genome,” the authors explained.
The researchers found that genes involved in fruit sugar content and acid metabolism are located in genomic regions that are identical between varieties, showing that once humans had identified a jujube plant with a sweeter taste, only plants with those genes became widely cultivated.
“A lot of genes involved in cell wall metabolism were changed between the two species,” said Dr. Zhangjun Fei, a researcher at the Boyce Thompson Institute.
“Between the dried and fresh, the cell wall structure was totally different.”
The study provides insights into how the jujube has evolved under human cultivation and the role of domestication in shaping its genome.
“Tree breeding and domestication is much harder than vegetables because it’s a long process,” Dr. Fei said.
“One generation from seeds to fruit sometimes takes several years.”
The work also provides a valuable genomic resource for breeders working to create improved jujube varieties, and may be applicable to the study of other fruit trees, such as apples, which are under intensive breeding to produce fruit with the best flavor.
The findings were published online this week in the journal PLoS Genetics.
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J. Huang et al. 2016. The Jujube Genome Provides Insights into Genome Evolution and the Domestication of Sweetness/Acidity Taste in Fruit Trees. PLoS Genet 12 (12): e1006433; doi: 10.1371/journal.pgen.1006433
