The secret of the corpse flower revealed

Nov. 11 () –

Dartmouth College scientists detect genes that cause corpse flower’s pungent odor -whose aroma is reminiscent of rotten meat- and which is exhibited in greenhouses around the world.

In their paper in PNAS Nexus, the team of scientists led by G. Eric Schaller, professor of biological sciences, also identifies a new component of the odor of this plant, also called giant arum: an organic chemical called putrescine.

Schaller, a molecular biologist who studies how plant hormones regulate their ability to grow and respond to changes in their environment, moonlights as a writer of short fiction, particularly horror fiction. “The corpse flower fits well into both worlds,” he says. in a statement.

Schaller and his collaborators took advantage of several flowers from Morphy, Dartmouth’s 21-year-old corpse flower housed in the life sciences greenhouse, to collect tissue samples for genetic and chemical analysis.

The giant arum is not a single flower, but a group of small flowers hidden within a gigantic central stem called a spadix, which can grow up to 3.6 meters tall and is the most striking visual feature of the plant.

The plant can go years without flowering (an interval of 5 to 7 years is typical), but when it does, it blooms overnight. “Flowers are rare and also short-lived, so we only have a small window to study these phenomena,” says Schaller.

A ruffled petal-shaped layer at the base of the spadix called a spathe unfolds to create a cup around the central stem that is dark red or brown on the inside. The spadix begins to heat up, rising up to 11 degrees Celsius above room temperature, followed shortly thereafter by the release of the plant’s characteristic aroma derived from a cocktail of stinking sulfur-based compounds that attract flies and carrion beetles. that help propagate the plant.

When the Morphy specimen in the Dartmouth greenhouse flowered in 2016, the researchers collected nine tissue samples over three nights from the time the spadix’s temperature peaked: from the lip and base of the spathe and from the towering spike. of the spadix known as the appendix. They later added two additional leaf samples to their collection.

Alveena Zulfiqar, an exchange researcher working in Schaller’s lab at the time, discovered how to extract high-quality RNA from the tissue, allowing the team to perform RNA-seq analysis. and determine the role genes play in warming the plant and causing the odor.

“This helps us see which genes are being expressed and which ones are specifically active when the appendix is ​​heated and emits odor,” Schaller says.

Thermogenesis, or the ability to generate heat, is common in animals, but rare in plants. In animal cells, a class of proteins called uncoupling proteins disrupt the chemical energy storage process, releasing it in place as heatsays Schaller.

RNA analysis revealed that genes associated with the plant counterparts of these proteins, known as alternative oxidases, showed increased expression in tissues extracted when flowering began, particularly in the appendage. They were also active at that time genes involved in sulfur transport and metabolism.

To track the mechanisms at play by these genes, the team isolated tissues from the plant during a later flowering period and, working with collaborators at the University of Missouri, used a technique called mass spectrometry to identify and measure the levels of different amino acids ( molecules that form proteins) in them.

As predicted from their RNA analysis, they detected high levels of a sulfur-containing amino acid called methionine, a precursor to sulfur-based compounds that vaporize easily when heated, producing pungent odors. Methionine levels dropped rapidly in the extracted tissues a few hours later.

What was surprising, Schaller says, was the detection of elevated levels of another amino acid in tissues taken from the spathe, which serves as a precursor for the production of the compound, putrescine, an odor found in dead animals when they begin to rot. .

This study is the first to unravel the secrets of the corpse flower stench at the molecular level, determine the processes by which the giant arum regulates temperature, and identify the roles played by different parts of the floral cluster. in the creation of the carrion colony that attracts pollinators.

Morphy holds more mysteries, says Schaller, who is now focused on understanding the triggers that predict flowering and whether specimens housed together could synchronize blooms to collectively increase odor level. and attract even more pollinators.