Asian Pathogen Threatens Florida's Citrus Crops
Florida's vital citrus industry is under siege. Federal officials sounded the alarm in early September after sickly pummelo trees turned out to have been infected by a deadly microbe originally from Asia. Huanglongbing, which means "yellow dragon disease" in Chinese, has already devastated citrus groves in Asia, Africa, and South America and now threatens Florida's orange and grapefruit crops. "Wherever the disease has shown up, it's been pretty bad," says Ronald Brlansky, a University of Florida plant pathologist. "They've quit growing citrus in those areas for years until it goes away."
Huanglongbing is one of eight plant pathogens on the U.S. Federal Register's list of "bioterrorism select agents." But the culprit spreading the disease is probably the Asian citrus psyllid, an aphid-size insect first sighted in Florida in 1998. An infected tree may take a few months to several years to show signs of sickness, and by then it's often too late. "The leaves turn yellow and drop, and the fruit becomes bitter and misshapen, making it useless," says Caitlyn Allen, a University of Wisconsin plant pathologist. "Once the tree has it, it's toast."
There is no cure, save a painstaking regime of antibiotic injections that are prohibitively expensive and not certain to work. Most infected trees are simply burned. For now, growers have few options, except to be vigilant. "They try to live with it, try to stay ahead of it," says Brlansky. —Jessa Forte Netting
Further Adventures Of J. Craig Venter
When last we heard from J. Craig Venter, he was sailing around the world in his 95-foot sloop, Sorcerer II, collecting water samples from the sea and inland lakes. So far the voyage, which started in Nova Scotia and is now in the Caribbean, has more than doubled the number of known microorganisms—and uncovered millions of new genes. In 2005 Venter also began collecting and cataloging the microorganisms of urban air, starting with those floating in Midtown Manhattan. The J. Craig Venter Institute, a not-for-profit research group of more than 200 scientists and staff members, sequences the genes using the same techniques Venter developed to decode the human genome.
At the same time, institute scientists are trying to build new genes that have never existed on Earth. They hope to synthesize genes for specific purposes—the production of hydrogen, for instance. They are also sequencing cancer genes. Meanwhile, the institute is offering a $500,000 prize to anyone who can come up with a technique that would provide a full DNA analysis of a human for $1,000 or less.
In August Venter purchased the Norman Collection of microbiology archives, which contains the papers of genome pioneers like Francis Crick, James Watson, Rosalind Franklin, and Linus Pauling. It will be made available to researchers at the institute's Maryland headquarters. And if that isn't enough, keep an eye out for the institute's mobile education lab, a bus coming soon to a school near you. —Bruce Stutz
Plants Mend Their Own Faulty DNA
Upending a fundamental tenet of inheritance that has long served as the foundation of genetic theory, a study published in March revealed that plants can correct defective genes inherited from their parents by reverting to an ancestral gene sequence. A Purdue University research team led by Robert Pruitt and Susan Lolle stumbled onto this discovery while working with Arabidopsis, a member of the mustard family that is a favorite experimental model. The parent generation had a mutant version of a gene dubbed hothead, which causes the plants to have fused flowers. Even when each parent carried two mutant versions of the gene, 10 percent of the next generation had normal flowers. Pruitt and his colleagues found that these plants had somehow retrieved ancestral code that allowed them to repair the mutant gene.
Although the discovery was made in plants, Pruitt suspects that animals, including humans, might also use this method to correct faulty genes. "There's another way that genetic information can be inherited, which we've been blissfully unaware of the last 100 years or so," Pruitt says. "To me that just boggles the mind. Then you really start to wonder what else is out there." —Apoorva Mandavilli
Sequence of X Chromosome Holds Surprises for Men and Women
In March an international team of almost 300 scientists announced the provocative results of sequencing the X chromosome. Women carry two versions of the chromosome, while men, in addition to the Y chromosome, carry only one.
Researchers hope to use these data to pinpoint genes responsible for more than 100 poorly understood X-linked diseases. Meanwhile, they've found that although the X chromosome contains a meager 1,098 genes, 10 percent of them are turned on in the testes. And in a separate study, researchers have already used the sequence to chart a surprising degree of genetic variation among women.
The project leader, Mark Ross of the Wellcome Trust Sanger Institute in Hinxton, England, speculates that it may not be advantageous for some genes to be on the X chromosome because of its unequal distribution among men and women. On the other hand, gene variants that confer a benefit to males are more likely to accumulate on the X chromosome than on a nonsex chromosome because they will always be expressed on a male's single X chromosome. This might explain why about 10 percent of the genes newly identified on the X chromosome are turned on mainly in the testes, even though little is known about their function.
Inheriting a single X chromosome exposes men to a host of X-linked diseases, such as hemophilia or Duchenne muscular dystrophy, and researchers hope to use the new data to understand more fully the role of genes in other X-linked conditions. Women tend to be protected from diseases related to genes on the X because female cells randomly inactivate one of the X chromosomes, and that leaves some cells with a normal copy up and running.
Using the new data, Laura Carrel, a geneticist at Pennsylvania State College of Medicine in Hershey, and Huntington Willard, a geneticist at Duke University in Durham, North Carolina, discovered that 15 percent of the genes on the inactivated X chromosome are actually not silenced—and most are likely to be expressed at higher levels overall in women than men. Another 10 percent of the genes on the turned-down chromosome vary substantially in the degree of activity from woman to woman. Ross, who wasn't involved in the work, believes the scattershot silencing may prove "a source of considerable genetic variation." What that variation means remains an open question. —Erik Stokstad
Single Gene Transforms Fish in One Generation
A thumb-size fish has changed the way scientists think about evolution. In a study reported in March, a research team found that a variation in a single gene makes all the difference between ocean-going sticklebacks, which are covered in 35 bony plates to protect them from predators, and the many species of sleeker, minimally plated freshwater sticklebacks. "Evolution in wild populations is thus both simpler than many researchers would have predicted and more reproducible," says vertebrate geneticist David Kingsley of the Stanford University School of Medicine.
Kingsley's laboratory has spearheaded recent research into the little fish. Last year, he and his colleagues found that sticklebacks can lose their spined pelvic fins in one generation after moving from salt water to freshwater, which demonstrates rapid evolution. Both studies show that a collection of minute changes over a long period of time is not required to produce fundamental transformation. —Jessa Forte Netting