Scientists decode genome of mold that causes potato infection

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Washington, September 10 (ANI): An international team of scientists has decoded the full genetic sequence, or genome, of Phytophthora infestans, which is a water mold that causes the serious potato disease known as late blight or potato blight.

The genome resulted from a large international effort to understand the genetics of a plant disease that has evaded many control efforts.

"This pathogen has an exquisite ability to adapt and change, and that's what makes it so dangerous," said senior author Chad Nusbaum, co-director of the Genome Sequencing and Analysis Program at the Broad Institute of MIT and Harvard, which directed the sequencing project.

About 75 percent of the genome contains repetitious DNA, which is now seen as key to understanding late blight's destructive potential.

"We now have a comprehensive view of its genome, revealing the unusual properties that drive its remarkable adaptability. Hopefully, this knowledge can foster novel approaches to diagnose and respond to outbreaks," said Nusbaum.

To cope with the confusing level of repetition, Broad Institute researchers contacted David Schwartz, a professor of chemistry and genetics at UW-Madison.chwartz was the principal inventor of the "optical mapping" system, which uniquely complements the traditional, letter-by-letter approach to gene sequencing.

The DNA of late blight contains about 240 million sub-units, or "bases."

To efficiently identify these units, scientists first cut the DNA into shorter chunks, and later digitally reassemble the chunks into one long sequence.

"It's full of repeated DNA sequences, so all the windows look the same and it's hard to know where the house should go. Combining the letter-by-letter information from sequencing with the broader view from optical mapping allowed us to put the genome together," said Schwartz.

The DNA chunks that used optical mapping "are much longer than those used in traditional sequencing and mapping, which means we can span lots of gaps that others cannot," said Shiguo Zhou, Schwartz's colleague in the Laboratory for Molecular and Computational Genomics and the principal scientist constructing the map.

"We can characterize regions where you see the same code repeated over and over and put whole genome together," he added.

The study found that the late blight genome is two and a half to four times larger than those of its relatives, mainly due to a massive amount of repetitive DNA. lthough these repetitive regions contain only a few genes, they are specialized for attacking plants; so understanding the repetitions may help explain why late blight is such an effective plant pathogen.

The research group hopes that further exploration of the genome will reveal weak links in the organism's offensive strategy. (ANI)

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