Sweet potato: complex genome unlocked
Scientists from China and Germany trace the origin of the huge sweet potato genome back to a crossbreeding between two ancestors 50,000 years ago.
With a yield of 100 million tons per year the sweet potato has become the seventh most important crop in the world, and even continues to gain popularity worldwide and in Germany. Thus, researchers are also focussing more and more on this extraordinary plant. An international team of researchers based in China and Germany and including the Max Planck Institute for Molecular Genetics in Berlin and the Max Planck Institute of Molecular Plant Physiology in Potsdam managed to decipher the complex genome of the sweet potato and published their results in the journal .
A difficult candidate for genome sequencing
In order to achieve higher yields or higher resistance against inclement weather patterns targeted breeding schemes are necessary, which are oftentimes only possible with deep understanding of the genetic material. Germany’s most important crop plants thus far have been the potato and wheat – both of which have been characterised in detail. Researchers from five different research institutes in China and Germany were able to sequence the complete genome of the sweet potato Ipomoea batatas. This plant belongs to the family Convolvulaceae and even before sequencing began it was clear that due to its complex genome the sweet potato would be a difficult candidate for a complete genome sequencing: the sweet potato has 90 chromosomes – even for plants an unusually high number.
The complex genome of the sweet potato was unlocked in a cooperation of these institutes:
Chenshan Botanical Garden in Shanghai (CSBG)
Max Planck Institute for Molecular Genetics in Berlin (MPIMG)
Shanghai Institute of Plant Physiology and Ecology (SIPPE)
Tai’an Academy of Agricultural Sciences in Shandong (TAAS)
Max Planck Institute of Molecular Plant Physiology in Potsdam (MPIMP)
Six sets of chromosomes
A diploid or double (2n) set of chromosomes is most common in nature. If there are more than two sets of chromosomes it is called polyploidy. Similarly to wheat the sweet potato does in fact have six sets of chromosomes – the plant is hexaploid. Such a genome duplication or multiplication can be caused by a faulty cell division, or environmental influences. Additionally, also cross breeding with related species can lead to genome multiplication.
In fact, the German-Chinese cooperation was able to show that the polyploid genome of the sweet potato can be traced back to a cross breeding 50,000 years ago: A diploid (2n) and a tatraploid (4n) ancestor plant crossed and lead to the hexaploid Ipomoea batatas.
Polyploidy provides evolutionary advantage
The researchers developed a novel haplotyping method with which they were able to unlock the origin of each single chromosome. Furthermore they could show that a number of genes have accumulated deleterious mutations on different alleles. This lead them to the assumption that the selection pressure on redundant chromosomes is much lower: because of the polyploidy sweet potatoes are evolutionarily advanced, since the additional sets of chromosomes can compensate for the ones that have collected mutations and can thus still produce a healthy and normal plant.