Sequencing the apple genome
The genome sequence of the Golden Delicious apple was published in 2010. It sheds light on the history of the apple and should make apple breeding faster and more accurate.
What’s in a genome?
Sequencing DNA
Sequencing machines can work out which DNA base is present at each position in a DNA fragment because each one is labelled with a different fluorescent molecule (shown as black, blue, green and red on the graph).
A is the complete set of that’s carried in each of an organism. It contains all the organism’s genes, as well as other sections of DNA that regulate activity and structure. There’s also a lot of DNA that has no known function at all.
‘Sequencing the genome’ means working out the exact order in which DNA bases (A, G, C and T) occur in an organism’s DNA.
The sequencing project: New Zealand’s role
The apple genome was a collaborative effort between Italy, the USA, Belgium, France and New Zealand. Golden Delicious is a key apple variety in Italy, which is why it was chosen for sequencing. New Zealand scientists provided access to Golden Delicious trees, in and a lot of hard work!
Find out more about the work undertaken by New Zealand scientists on m
The apple genome: lots of genes
The scientists who sequenced the apple genome made several unexpected findings. For one, it had a huge number of genes (approximately 57,000). This was more genes than had yet been found in a plant genome and twice as many as in the human genome. The apple genome also contained an unusually large number of transposons – short chunks of DNA that can ‘jump around’ within the genome sequence.
What the apple genome can tell us
Andy Allan of Plant & Food Research discusses what we can learn from the apple genome sequence (published in 2010) and how it will impact on breeding programmes.
What the apple genome can tell us
Andy Allan of Plant & Food Research discusses what we can learn from the apple genome sequence (published in 2010) and how it will impact on breeding programmes.
An Asian ancestor for apple
The apple genome sequence confirmed that the central Asian apple Malus sieversii is the ancestor of the modern apple – not the European apple Malus sylvestris , which has previously been proposed as an ancestor. Researchers worked this out by comparing the DNA sequence at many places within the Golden Delicious genome with the same place in the DNA of wild apple . They showed that Malus sieversii DNA had the most similarity to Golden Delicious at these sites.
This finding fits well with our current understanding of how the apple became domesticated. It is thought that Silk Route traders and their animals ate wild apples from Kazakhstan, helping them spread east to Europe and west to China. Programmes of domestication were then begun in these areas and eventually developed into programmes.
For further information read the article The germplasm collection: a library of apples.
The apple genome sequence and breeding
The apple genome sequence should make the apple breeding process considerably faster and more accurate. Because it tells us the location and sequence of every gene in the apple, it will enable the design of many more DNA markers for desirable traits. In turn, this should improve and – 2 breeding techniques that rely on DNA markers.
DNA markers and apple breeding
Andy Allan and Richard Espley, of Plant & Food Research, explain what DNA markers are and how they can be used to make apple breeding more efficient.
Select here to view the Teaching points, the full transcript and copyright information.
The article
It’s also likely that the genome of individual apple seedlings will be sequenced routinely in the future, when the cost of sequencing is less. Eventually, this might provide an alternative to marker-dependent breeding techniques.
The genome sequence also provides insight into how existing apples function. As the genomes of other apple cultivars are sequenced, it will help researchers understand the basis of important apple characteristics like flavour, texture and disease .
Useful links
Read the original research paper that reported the apple genome sequence (published in the journal Nature Genetics ).
These short videos give a step-by-step account of how a genome is sequenced (with specific reference to the human genome).
This article from PHYS.ORG explores the history of the apple from its wild origins.
