New Research Maps Molecular Basis of Chiral Mirror-Image Flowers

A two-gene supergene and gravity work together to give butterfly lily flowers their rare floral left- and right-handedness, which improves pollen transfer, researchers say. The findings offer new insight into the development of unique mirror-image flowers.

Left-right asymmetry is a fundamental pattern in biology, seen in everything from the placement of internal organs to the coiling direction of snail shells. While the genetic and developmental mechanisms controlling this asymmetry are well understood in some animals, naturally occurring populations with both left- and right-sided forms are extremely rare. Mirror-image flowers in some plants provide a unique example, with left- and right-oriented floral structures that help prevent self-pollination and improve pollen transfer between individuals.

However, the developmental origins and genetic basis of this floral handedness remain poorly understood. Haoran Xue and colleagues examined how reproductive organs are positioned during butterfly lily (W. paniculata) flower development and identified the genetic basis of this process by analyzing the genes associated with left- and right-handed flowers. Xue et al. found that the orientation of female and male organs is determined by a combination of genetically controlled chirality and gravitropism (a directional growth response to gravity), which allows the organs to orient relative to gravity rather than the flower's internal structure.

The authors also identified a supergene containing two candidate genes, MIR156-R and YUCCA-R, that independently control the orientation of the female and male organs. This coordinated arrangement places pollen from left- and right-handed flowers on different parts of pollinators' bodies, promoting pollen transfer between flowers of opposite handedness and maintaining the species' reproductive characteristics.