N.C. State, international effort reveals peach genome
The peach genome sequence should be particularly useful to plant breeders who want to develop peaches with particular characteristics or, perhaps, to use genetic transformation techniques to move desirable peach traits to other plants.Photo courtesy Dr. Bryon Sosinski
An international effort coordinated at N.C. State University that has revealed the genetic makeup of the peach could have far-reaching implications for the future of peaches as well as related plants such as roses, strawberries, raspberries, cherries, apples, plums and even poplar and chestnut trees.
Dr. Bryon Sosinski, associate professor of horticultural science, was the American coordinator of an effort to sequence the genome of the peach. Sosinski said the International Peach Genome Initiative (IPGI) spanned the globe, involving scientists in Italy, Spain and Chile. In the United States, N.C. State, the DOE Joint Genome Institute, Clemson University and Washington State University were the principal partners.
Sosinski said that in the U.S., the effort was funded by the U.S. Department of Energy, while the Italian government funded the international effort. He added that the peach genome sequence will be available online beginning April 1 at http://www.peachgenome.org.
When the genome of an organism is sequenced, scientists determine the order, or sequence, in which the nucleotides, or molecules, that make up DNA appear on chromosomes. These nucleotides are identified by the letters A,T,C,G, so a genome sequence is a long list of these letters.
While sequencing the genome of an organism is a significant scientific achievement, Sosinski said it is just the beginning of scientific work related to the genome. The genomic sequence of an organism is roughly equivalent to a book that is simply a long list of letters, without spaces between words or punctuation, paragraphs or chapters.
This long list of letters, by itself, has little meaning; however, if the letters are organized into words, and punctuation added, and sentences organized into paragraphs and chapters, the book begins to make sense.
Scientists will work with the peach genome sequence to create the scientific equivalent of a readable book by identifying areas of the genome and their functions. For example, not all the letters in a genomic sequence are genes. Indeed, some strings of letters have no discernable function and are known as junk DNA. Other letter strings do form genes, while other strings of letters have still other functions.
The genomes of a number of organisms, including humans, have been sequenced. Sosinski said those various genome sequences have not been created equally. Some are more accurate and thus more useful than others. He said the peach genome appears to be particularly accurate.
“In the plant world, this looks like it’s arguably one of the superior genomes out there,” Sosinski said. “It’s going to have a lot of utility.”
In other words, the peach genome sequence should be particularly useful to scientists like plant breeders who want to develop peaches with particular characteristics or, perhaps, to use genetic transformation techniques to move desirable peach traits to other plants.
Sosinski said the peach genome sequence is unusually accurate because the sequence was derived from a peach variety called ‘Lovell,’ which has a doubled haploid genome. A haploid cell, such as sperm and egg cells, is homozygous, containing only one set of chromosomes. Heterozygous cells, such as cells other than egg or sperm that make up the human body, are diploid, containing two sets of chromosomes. There are variations in the nucleotide sequences in these different sets of chromosomes.
“This is important because when an individual is heterozygous or largely heterozygous, the sister copies of the genes and DNA are different, making the assembly of the sequence problematic,” Sosinski explained.
He added, “Imagine if you took two jigsaw puzzles that had the same picture on them, but the pieces of each puzzle were cut differently, and you mixed the pieces of the two puzzles together, then tried to put them back together. Some of the pieces wouldn’t fit together properly. In our case, the pieces of the two puzzles are identical, so it doesn’t matter which puzzle a piece originally came from, it will fit correctly.”
Also adding to the accuracy of the peach sequence is the fact that the DNA content of the peach genome is relatively small at about 230 Mbp (millions of bases), as compared to over 2 billion bases for the corn genome.
Sosinski said the peach genome should be useful to scientists working with a number of peach relatives whose genomes appear to be similar to that of the peach. Some of these relatives, such as apple or plum, might be expected, but others, such as strawberries and raspberries and trees such as poplar and chestnut, would seem unlikely in that the plants are quite different from peaches.
It is likely, he added, that all these plants had common ancestors. While they have evolved to be quite different today, their genetic makeup remains similar. As a result, what scientists learn about the peach genome may transfer to these relatives, as the peach genome appears to be relatively unchanged or ancestral in nature. If, for example, scientists identify a peach gene that influences sugar content in the fruit, strawberries and raspberries may have that same gene, and it may have the same function.
The peach tree whose genome was sequenced is on the Clemson University campus, Sosinski said, and arrangements have been made to send 10 cuttings of the tree to NC State, where Sosinski hopes to plant the trees around campus.
The Department of Horticultural Science is part of N.C. State’s College of Agriculture and Life Sciences.
– Dave Caldwell