The DNA code of the Golden Delicious apple has been
sequenced for the first time.
A global team of 86 scientists from Italy, France,
New Zealand, Belgium, and the United States have published their
findings on the apple genome in Nature
Genetics. Researchers from Washington State
University and the UW
were among the contributors.
The breakthrough could help agricultural scientists selectively
breed new apple varieties that have desired traits—in appearance, color, taste,
and texture—and that are more resistant to disease and drought.
Apple, and its close relative, the pear, have 17
chromosomes. This is about twice the number of chromosomes in
other plants from this same family. Sequencing the apple's genome revealed
that large lengths of apple chromosomes are copied in other chromosomes. Many
of the duplicate genes in apple trees are related to fruit development.
The apple DNA study suggests that a major step in the
evolution of the apple coincided with a catastrophic event some
60 million years ago, and may have been a survival response during a time of
mass extinctions.
Washington State University
horticultural genomicist Amit Dhingra coordinated the Washington state portion of the
international study. This part of the study included sequencing and analyzing a
unique version of the genome of the Golden Delicious apple in which all
duplicated chromosomes are genetically identical. This information was used to
validate the sequence of the more complicated Golden Delicious apple in which
duplicated chromosomes are not identical.
Microbiologist Roger Bumgarner's lab at the UW provided the
initial sequencing expertise and capability to the project, which was later
complemented by sequencing expertise in the Dhingra genomics lab.
The international Apple Genome Study was coordinated by
Riccardo Velasco at the Edmund Mach Foundation in Italy.
The domestic apple is the main fruit crop of the world's
temperate regions. Apple is a member of the plant family Rosaceae which
includes many other economically important species, including cherry, pear,
peach, apricot, strawberry, and rose, to name just a few.
After the apple sequencing was completed, WSU computational
biologist Ananth Kalyanaraman compared its genome with that of pear, peach and
grape to identify the differences and commonalities between these fruit crops.
The state of Washington
accounts for approximately 60% of total apple production in the United States.
Rosaceae fruit production is a multi-billion dollar industry in the state.
Where did the apple originate? Scientists have long wanted
to know—and have for years argued vehemently about—the ancestor of the modern
domesticated apple. The question is now settled. Malus sieversii, native to the mountains
of southern Kazakhstan,
is the apple's wild ancestor, according to the Nature Genetics paper. It appeared about 4,000
years ago. There are now more than 7,500 known varieties of apple.
"Having the apple genome sequence will greatly
accelerate our ability to define the differences between apple cultivars at the
genetic level," said Kate Evans, an apple breeder based at the WSU Tree
Fruit Research and Extension
Center. "This will
allow us to exploit these differences and target areas of diversity to
incorporate into the breeding program. We hope these will result in cultivars
that are better for consumers and for long-term, sustainable production."
"Before genome sequencing, the best we could do was
correlate traits with genes. Now we can point to a specific gene and say, 'This
is the one; this gene is responsible for this trait'. That trait of interest
might be, for instance, a disease. Or the trait might be for something
desirable, like flavor in a piece of fruit. We are already working on finding
physiological solutions to issues like bitter pit in current apple varieties
with the gene-based information available to us," Dhingra said
Dan Bernardo, dean of the WSU College of Agricultural,
Human, and Natural Resource Sciences, said, "The Washington apple is an icon of quality
around the globe. Washington
is a natural home for the advanced science necessary to map the tree fruit
genome and actively study how it functions."
The United States
portion of the apple genome project was supported by a National Research
Initiative competitive grant from the USDA National Institute of Food and
Agriculture and the Washington Tree Fruit Research Commission. Additional
funding came from the WSU Department of Horticulture and Landscape Architecture
and the Agriculture
Research Center
at WSU.
SOURCE
