Butterfly lilies wing their way to Science
University of Cape Town - Faculty of Science
image:
A genetic switch determines left–right floral asymmetry in Wachendorfia and Barberetta mirror-image flowers
view moreCredit: Nicola Illing
The inner genetic secrets of how the flowers of butterfly lilies break left-right symmetry have been revealed for the first time in a paper published in the prestigious journal Science. An international team of scientists, including researchers and students from the University of Cape Town (UCT), has answered this century-old evolutionary curiosity, noted by an English naturalist and biologist Charles Darwin, nine days before his death, in a letter addressed to a professor of natural science at Tabor College, James E Todd, in America.
The study reveals, for the first time, the genetic and developmental mechanisms that determine the “handedness” of butterfly lilies (Wachendorfia), a genus of plants found only in South Africa’s Western and Eastern Cape and in a sister genus, Barberetta aurea found in KwaZulu-Natal and the Eastern Cape. The discovery sheds new light on one of biology’s most fundamental questions: How do living organisms break left-right symmetry during development?
Most animals and flowers are either radially or bilaterally symmetrical. Yet many organisms break this symmetry in remarkable ways. In humans, for example, the heart develops on the left side of the body. Butterfly lilies have evolved their own version of this phenomenon. Every flower on an individual plant develops with its female style pointing either to the left or to the right, while the central stamen deflects in the opposite direction. This ingenious arrangement reduces self-pollination and promotes efficient transfer of pollen between flowers of opposite orientation.
The research brought together scientists from UCT, the University of Potsdam and Wageningen University, with support from the Human Frontier Science Program and the South Africa 1KSA project. Researchers from UCT’s Department of Molecular and Cell Biology, together with postgraduate students, played a pivotal role in solving the puzzle.
“This study addresses a fascinating question that has puzzled evolutionary biologists for well over a century,” said Professor Nicola Illing from UCT’s Department of Molecular and Cell Biology. “By identifying the genes responsible for right-floral handedness, and conducting experiments on developing flower buds, we’ve uncovered the cues that determine how Wachendorfia and Barberetta flowers break symmetry, and whether a flower becomes left- or right-oriented.”
Research process
One of the project’s earliest hurdles was obtaining high-quality deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) from butterfly lilies, whose tissues are rich in sticky carbohydrates that complicate genetic studies. During her MSc research, Kelly Shepherd developed a protocol that successfully extracted high-quality genetic material from developing flower buds, laying the foundation for the team’s genomic analyses.
Comparing the DNA of hundreds of left- and right-oriented plants across four Wachendorfia species and B. aurea enabled the researchers to identify a segment of DNA found only in right-oriented plants. Further investigation revealed two closely linked genes, YUC-R and miR156, that switch the flower’s default left-oriented developmental programme into a right-oriented one before the style and stamen begin to bend.
UCT honours students Oliver Marketos and Anand Shankar provided further evidence by demonstrating that the butterfly lily version of miR156 performs the same regulatory function as the equivalent gene in the model plant Arabidopsis thaliana.
The team also embarked on a frenzied hunt across the Western Cape for naturally occurring butterfly lily mutants. Genetic analysis by Olivia Page-MacDonald demonstrated that these mutants were a natural test of the handedness genes’ function. When YUC-R was defective, the central stamen changed its deflection from left to the right, while if miR156 was defective, the style deflected to the left, instead of the right. These results provide compelling proof that YUC-R and miR156 control the flower’s handedness.
Significant discoveries
Professor Illing said one of the study’s most significant discoveries came unexpectedly. While recording flower development, she accidentally positioned a flower bud upside down. MSc student Caroline Robertson made the key observation that instead of continuing its normal growth, the developing flower reversed the orientation of its style and stamen.
“Scientific breakthroughs don’t always happen exactly as planned. This unexpected observation showed us that gravity provides an important directional cue as the flower develops. It was a remarkable moment that transformed our understanding of how these beautiful flowers establish their left-right orientation,” added Associate Professor Robert Ingle from UCT’s Department of Molecular and Cell Biology.
Beyond solving a long-standing evolutionary puzzle, the findings deepen scientists’ understanding of how genes, environmental signals and developmental processes interact to shape the extraordinary diversity of life.
As spring approaches, South Africans will have the opportunity to see these remarkable plants in bloom. The marsh butterfly lily (Wachendorfia thyrsiflora) grows along streams in the Western Cape and in botanical gardens around the world, while Wachendorfia brachyandra, Wachendorfia multiflora, and Wachendorfia paniculata can be found flowering across the Western Cape, from the Cederberg to Cape Agulhas, from August to November.
How asymmetric butterfly-lily flowers promote outcrossing [VIDEO]
How asymmetric butterfly-lily flowers promote outcrossing
Animation illustrating how the transfer of pollen from a butterfly lily flower onto the wings of an insect ensures efficient pollen transfer between left- and right-morph flowers and vice versa. This is followed by live footage of a beefly (Australoechus hirtus) probing Wachendorfia paniculata flowers at Waylands, Darling, South Africa. Note how the wings beat against the opposing stamen and the style.
Credit
Nicola Illing and Olivia Page-MacDonald
Journal
Science
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
Supergene control of chiral development in mirror-image flowers
No comments:
Post a Comment