The invisible colors of sunflowers help attract bees and adapt to drought

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It turns out that sunflowers are more than just a pretty face: The ultraviolet colors of their flowers not only attract pollinators, but also help the plant regulate water loss, according to new research from the University of British Columbia.

The dense cluster of yellow petals of a sunflower (technically the ‘inflorescence’, or a cluster of many flowers) is a familiar sight, but it hides something from the human eye: a bullseye ultraviolet (UV) pattern, invisible to humans but not most insects. Including bees.

These Paulus patterns have long been known to improve flowers’ attractiveness to pollinators by increasing their appearance. Now, University of British Columbia researchers have found that the same molecules that produce patterns of UV radiation in sunflowers are also involved in helping the plant respond to stresses such as drought or temperature extremes, in a new paper published today in eLife, likely to provide clues to how plants adapt to different climates.

“Unexpectedly, we noticed that sunflowers growing in drier climates had flowers with larger flowers than UV rays, and we found that these flowers are able to retain water more efficiently. This indicates that these large flowers are Ultraviolet light helps plants adapt to these drier environments,” Dr. Marco Todesco, Research Associate in the Biodiversity Research Center and Department of Botany at the University of British Columbia.

Dr. Todesko and colleagues planted nearly 2,000 wild sunflowers of two species at the university in 2016 and 2019. They measured the UV patterns of sunflowers, analyzed the plants’ genomes, and found that wild sunflowers from different parts of North America had them. UV bulls are of very different sizes: in some, the target was a thin ring, while in others it covered the entire flower. Big bulls were frequently visited by bees, supporting previous research for other plant species.

The researchers found that a single gene, HaMYB111, was responsible for most of the diversity in ultraviolet flower patterns. This gene controls the production of UV-absorbing flavonols, which are also known to help plants survive under various environmental stresses such as drought or temperature extremes. Large floral UV patterns with more of these compounds can help reduce the amount of evaporation from sunflowers in environments with low humidity, preventing excessive water loss. The authors say that smaller UV patterns in humid and hot environments would instead enhance this evaporation, keeping the plant cool and avoiding overheating.

“Ultraviolet floral patterns appear to play at least a dual role in adaptation; besides their well-known effect of promoting pollination, they also regulate water loss from flowers,” says senior author Dr. Lauren Riesberg, professor in the Department of Botany and Biodiversity Research Center. . “It’s not necessarily something you’d expect from flower color, and it represents the complexity and efficacy of an adaptation — solving two problems with one trait.”

Sunflowers are grown for various purposes, including the production of sunflower oil, an industry worth about US$20 billion in 2020. This research could help add knowledge about how to attract pollinators, which could lead to higher crop yields, he says Dr. Todesko. “This work also helps us understand how sunflowers, and possibly other plants, better adapt to different regions or temperatures, which can be important in hot climates.”

The researchers also want to better understand how HaMYB111 regulates the size of ultraviolet oxen, examine in more detail how these patterns affect plant physiology as well as investigate exactly how flavonols affect water loss.

more information:
Marco Todesco et al., Genetic basis and dual adaptive role of floral pigmentation in sunflowers, eLife (2022). DOI: 10.7554 / eLife.72072

Journal information:

Provided by University of British Columbia

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