Hot potato news

A research team based in Germany and China has announced the first sequencing and assembly of a potato genome.

Potatoes have a tetraploid genome, meaning that they have four copies of each chromosome – two copies inherited from each plant parent.

Humans and most other animals have diploid genomes – we have two copies of each chromosome, one from each parent. However, because of differences between plant and animal reproduction, it’s not uncommon for plant genomes to be tetraploid or even hexaploid (six copies).

Four copies of each chromosome means four copies of each gene, and this presents some difficulty for both scientists and farmers seeking to understand the potato.

For one, the number of potential combinations of gene variations (alleles) makes it more complicated to reliably breed new varieties of potato with desirable traits.

When it comes to genome sequencing, having similar data from four different copies of a gene rather than only two makes it more challenging to figure out how all the sequences fit together. 

Potato genome concept a cartoon showing a haploid genome with one copy of each chromosome, a diploid genome with two copies of each chromosome, a triploid with three copies and a tetraploid with four copies
Ploidy refers to the number of copies of each chromosome a genome has: the human genome is diploid (two copies of each chromosome), while the potato genome is tetraploid (four copies). Credit: Ehamberg / Wikimedia Commons.

The research team developed a clever approach to circumvent this latter problem and successfully reconstruct the potato genome.

Instead of trying to use DNA from ordinary tetraploid potato cells, they focused their sequencing effort on the plant’s pollen cells.

Pollen is part of the plant reproductive system. It contains the male gametes (sex cells), making it roughly analogous to sperm in animals.

Because sex cells fuse together to create offspring, they contain half as many chromosome copies as the other cells, so that the offspring ends up with the right number of copies.

In humans, sperm and egg cells have only one copy of each chromosome, with the offspring ending up with two copies. For the tetraploid potato, the pollen cells contain only two copies of each chromosome, rather than four.

By sequencing the pollen cells, the research team successfully reduced the complexity of the data to the point that they could reconstruct the entire potato genome.

Potato genome concept two potatoes in foreground with potato leaves and flowers in the background
Before the potato was recognized as edible, it was grown in Europe as an ornamental plant. The pollen in the large flowers is normally collected by bumblebees for pollination. In the new study, genomes from individual pollen grains were analysed to produce the first complete map of a potato genome. Credit: Ulrich Pollmann.

The work was led by Hequan Sun and Korbinian Schneeberger, of the Max Planck Institute for Plant Breeding Research and LMU Munich in Germany.

The researchers hope that making the full potato genome available will pave the way to more successful breeding of new potato varieties, allowing breeders to more easily identify which genes or variants are desirable or undesirable for future crops.

“Building on this work, we can now implement genome-assisted breeding of new potato varieties that will be more productive and also resistant to climate change,” says Schneeberger.

“This could have a huge impact on delivering food security in the decades to come.”

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