This parasite turns plants into zombies
News and notes about science
Amustard plant infected with a certain parasite grows strangely, its development warped by tiny invaders. Its leaves take on odd shapes, its stems form a bushy structure and it may grow flowers that do not produce seed. Most peculiarly of all, it lives longer than its uninfected brethren, in a state of perpetual adolescence.
“It looks like it stays in a juvenile phase,” said Saskia Hogenhout, a scientist at the John Innes Centre in England, who studies the life cycle of the parasite, called Aster Yellows phytoplasma.
The plant’s neighbors grow old, reproduce and die, but the phytoplasma’s eerily youthful host persists. It becomes something like a mix between a vampire that never ages and a zombie host whose body serves the needs of its parasite, namely, tempting sap-sucking insects to feast on the plant’s bodily fluids as long as possible. When the insects ingest the parasite, they spread it to new hosts, and the whole “Night of the Living Dead-meets-dracula” cycle repeats.
How the parasite exerts such wide-ranging control is a subject of more than casual curiosity among scientists — phytoplasmas can cause destructive disease in crop plants such as carrots. In a paper published in September in the journal Cell, Hogenhout and her colleagues reveal that some of these creepy alterations are driven by the work of a single protein from the parasite called SAP05, which stands in the way of the plant’s maturation.
SAP05 is not the first substance made by this phytoplasma that the scientists have linked to the symptoms it causes. The team sequenced the parasite’s genome some time ago and has pinpointed a handful of proteins that it may use to zombify its victims. But in the new paper, they explain how SAP05 seems to drive some of the more surprising effects, including the life-span extension.
It turns out that SAP05 binds to two groups of plant proteins that control the expression of genes used in development. Once it latches onto them, it causes them to be broken down by the plant’s own garbage-disposal machinery. As a result, the plants appear frozen in time, unable to progress.
That makes sense, from the parasite’s perspective. If host plants were to mature normally, they would grow flowers and produce seeds, putting all of their energy toward making the next generation of plants. Before long, they would drop their leaves and wither away.
— Veronique Greenwood
This comet stays busy
One recent day, a speck of light shimmering in the shadows behind Jupiter erupted. And then it kept erupting, with two more violent jets of material firing into space the next day, followed by a fourth paroxysm the day after that. As it raged and flared, it became 250 times brighter than usual, like a lit match becoming a bonfire.
This is not a distant tempestuous star, nor is it an effervescent world covered in erupting volcanoes. This is Comet 29P. And it put on the performance of a lifetime that anyone with a powerful enough backyard telescope could see.
As far as astronomers are aware, this is the first time that this comet has exhibited four closely spaced eruptions.
“Some are calling this a super outburst,” said Maria Womack, an astrophysicist at the National Science Foundation. “This requires an immense amount of energy.”
What’s causing this comet’s riotous cascade?
“We don’t know,” Womack said. “And that’s what makes it so interesting.”
Comets are icy leftovers from the anarchic birth of the solar system that occasionally are yanked by the forces of gravity toward the sun. Each comet is novel in its own way. But Comet 29P/schwassmann-wachmann — or 29P — is “odd on many levels,” said Kacper Wierzchoś, an astronomer at the University of Arizona.
Unlike most comets, it does not dramatically plunge toward the sun before zipping back out to the outermost frontier of the solar system. Instead, this 37-mile-wide ball of ice revolves around the sun in the space between Jupiter and Saturn — making it a type of object known as a centaur — on a freakish, near-circular orbit, completing one circumnavigation every 14.6 years.
Despite being 560 million miles from the sun, 29P is in a state of near-constant fury, frequently blasting gas and dust into the enveloping dark. It is “always active and never turns off,” Womack said.
This hyperactivity is perhaps a result of its preponderance of carbon monoxide — a volatile gas — which needs only a soupcon of sunlight to dramatically heat up and outgas into space in large volumes. These eruptions briefly brighten the comet’s atmosphere, or coma, by topping it up with sunlight-reflecting dust.
There are at least seven brightening outbursts per year. “No other known comet in the solar system undergoes outbursts with such frequency and intensity,” Wierzchoś said.
— Robin George Andrews
This may be the first planet found orbiting 3 stars at once
GW Ori is a star system 1,300 light years from Earth in the constellation of Orion. It is surrounded by a huge disk of dust and gas, a common feature of young star systems that are forming planets. But fascinatingly, it is a system with not one star, but three. As if that were not intriguing enough, GW Ori’s disk is split in two, almost like Saturn’s rings if they had a massive gap in between. And to make it even more bizarre, the outer ring is tilted at about 38 degrees.
Scientists have been trying to explain what is going on there. Some hypothesized that the gap in the disk could be the result of one or more planets forming in the system. If so, this would be the first known planet that orbits three stars at once, also known as a circumtriple planet.
Now the GW Ori system has been modeled in greater detail, and a research team led by Jeremy Smallwood, a recent PH.D. graduate from UNLV, say a planet — a gassy world as massive as Jupiter — is the best explanation for the gap in the dust cloud. Although the planet itself cannot be seen, astronomers may be witnessing it carve out its orbit in its first million years of its existence.
A paper on the finding was published in September in the Monthly Notices of the Royal Astronomical Society. The scientists say it disproves an alternative explanation — that the gravitational torque of the stars cleared the space in the disk. Their paper suggests there is not enough turbulence in the disk for this explanation to suffice.
The finding also highlights how much more there is to learn about the unexpected ways in which planets can form.
If a familiar life form could dwell on a gas giant like the one that would be orbiting GW Ori, it would not actually be able to see the three stars in its skies. Rather, they would see only a pair as the two innermost stars orbit so close as to appear like a single point of light. Yet as the planet rotated, its stars would rise and fall in fascinating sunrises and sunsets unlike any other known world.
Scientists looking for a planet orbiting three stars found potential evidence in another system, GG Tau A, about 450 light years from Earth. But the researchers say the gap in GW Ori’s gas and dust ring makes it a more convincing example. — Jonathan O’callaghan
Volcanic eruptions helped dinosaurs dominate planet Earth
The relationship between dinosaurs and volcanoes has historically not always appeared so amiable.
For decades, scientists argued over whether volcanoes or an asteroid caused dinosaurs’ abrupt extinction 65 million years ago. It wasn’t until 2010 that an international panel of experts formally declared that it was the space rock, and not giant eruptions, that was the primary cause of dino demise.
Now, a team of researchers is presenting the most compelling evidence yet that massive volcanic events probably helped the dinosaurs take over the planet, at least in another era. Their results were recently published in the Proceedings of the National Academy of Sciences.
The Triassic Period, which began 250 million years ago, was a time of massive ecological change following the largest mass extinction event on record. Although dinosaurs had emerged in this time period, they were different: skinnier, more reptilian-looking, less of the toothy box-office hits we flock to movie theaters to see. But it was during this time period that dinosaurs diversified until they became wondrous beasts such as Tyrannosaurus rex or the triceratops that dominated ecosystems all over Earth through the end of the Cretaceous period.
To understand what drove this dinosaur transformation, scientists looked at a phase spanning 2 million years during the Triassic Period known as the Carnian Pluvial Episode, or CPE. During that episode, from 234 million to 232 million years ago, the planet experienced an increase in global temperature, humidity and rainfall — a climate often referred to as a “megamonsoon.”
The researchers analyzed sediment and plant fossil evidence from a lake in Northern China and were able to match four intense phases of volcanic activity with the changes of the CPE.
Previously, researchers had hypothesized that global carbon cycle changes during the episode were the result of major volcanic eruptions from what is now a mass of igneous rock found throughout western North America. The new study links the timing of the episode with four distinct peaks in mercury — a well-established indicator of volcanic activity — to carbon cycle shifts as well as rainfall, which led to local changes in the vegetation on land and in the lake.
“We’re often able to link volcanism to global warming, but our study is unusual in that we’ve also linked it to periods of intense rainfall,” said Jason Hilton, a paleobotanist and a study co-author. — Sam Jones