How many petals?

The APETALA1 gene in hairy bittercress plants lost the ability to ensure that its flowers all have the same number of petals.
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Hairy Bittercress. Image credit: Björn S. (CC BY-SA 2.0)

Many plants produce flowers that attract insects to land on them. Different insects are attracted to flowers of different shapes and colors. Therefore, it is generally advantageous for plants of the same species to produce flowers that look very similar.

For example, a small weed known as Arabidopsis – which is often used in research studies – produces little white flowers that all have four petals. Thus, the number of petals in Arabidopsis flowers is said to be a ‘robust’ trait. However, a closely-related plant called hairy bittercress produces flowers with any number of petals between zero and four. Studying the genetic differences between Arabidopsis and hairy bittercress can help to reveal why the numbers of petals on hairy bittercress flowers vary.

A gene called APETALA1 helps to control how petals form. Monniaux, Pieper et al. found that Arabidopsis and hairy bittercress have different versions of this gene that determine whether the number of petals may vary between individual flowers. Inserting the Arabidopsis version of APETALA1 into hairy bittercress plants caused the plants to produce flowers that had more similar numbers of petals to each other, that is, the petal number became more robust.

Monniaux, Pieper et al. then used a statistical method called quantitative trait locus analysis to identify the precise location of regions in the hairy bittercress genome that control petal number. This showed that the Arabidopsis version of APETALA1, but not the hairy bittercress version, conceals the action of these genes that could alter petal number.

These findings reveal that evolutionary change in a single gene of hairy bittercress unmasked the action of other genes that caused petal number to vary. A next step will be to identify some of these genes and understand how they control petal number.