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Where do Flowers Come From? Shedding Light on Darwin’s ‘abominable mystery’

​The mystery that is the origin of flowering plants has been partially solved. A team from CEA-BIG and their partners have shed light on a question that much intrigued Darwin: the appearance of a structure as complex as the flower over the course of evolution.
Published on 24 February 2017

Terrestrial flora today is dominated by flowering plants. A group, known as gymnosperms, with a more rudimentary mode of reproduction, directly preceded flowering plants. Conifers are among its modern-day representatives. Darwin long pondered the origin and rapid diversification of flowering plants, describing them as an "abominable mystery." In comparison with gymnosperms, which possess rather rudimentary male and female cones (like the pine cone), flowering plants present several innovations: the flower contains the male organs (stamens) and the female organs (pistil), surrounded by petals and sepals; while the ovules, instead of being naked, are protected within the pistil.

How was nature able to invent the flower, a structure so different from that of cones? In collaboration with CNRS and Kew Gardens in the UK, a team from CEA-BIG has just provided part of the answer. To do so, the researchers studied a rather original gymnosperm called Welwitschia mirabilis. This plant, which can live for more than a millennium, grows in an extreme desert environment in Namibia and Angola. Like other gymnosperms, it possesses separate male and female cones. What is exceptional is that the male cones possess a few sterile ovules and nectar, which indicates a failed attempt to evolve a bisexual flower. Yet, in this plant (as well as in certain conifers), the researchers found genes similar to those responsible for the formation of flowers, and which are organized according to the same hierarchy (with the activation of one gene activating the next gene, etc.)!

The fact that a similar gene cascade has been found in flowering plants and their gymnosperm cousins indicates that this was inherited from a common ancestor. This mechanism did not have to be invented at the time of the origins of the flower: it was simply inherited and reused by the plant, a process that is often at work in evolution. The study of the current biodiversity of plants thus enables us to go back in time and gradually sketch the genetic portrait of the common ancestor of a large proportion of modern-day flowers. The team is continuing to study other traits to better understand how the first flower emerged.

This result was the subject of a press release.

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