Roses are red, violets are blue, because flowers need sunscreen and pollinators too

Flower petals, like the pink and white ones above, are a display to attract animals like bees, moths, birds, and even lemurs, who carry pollen from flower to flower. Plants color their petals (and seeds, fruits and leaves) with classes of molecules known as flavonoids (2).

Flavonoids are produced through a biosynthetic pathway which is a chain of events catalyzed by enzymes that creates particular molecules as products. Think of a recipe for chocolate chip cookies: there are lots of components that go into the dough (chocolate chips, flour, butter, sugar, baking soda). However, they don't make that crispy, buttery cookie (crispy is my favorite cookie, by the way) until we add a little heat and time. In the biosynthesis of a molecule, we need some starter molecules and then the "heat" in the form of enzymes to get things cooking.

This is what a flavonoid looks like:

The molecule starts a long way from this finished product though. It begins looking like this:


So, the start of a pigment recipe is not too different from the cookie recipe.

The beginning  of a cookie recipe might look a lot like this:

With a little work (and a few more ingredients) we get the glorious vision seen here:

How do we get from the flour, baking soda, sugar, and butter to the timeless gooey (if you prefer those) goodness of a cookie? Before we can even mix the cookie (or flavonoid) ingredients together, there is something else we need -- the instructions. In biosynthesis, this information is encoded in the genes for flavonoid production. A gene (or set of genes) gives the instructional information for releasing an enzyme that catalyzes the chain of reactions leading to a flavonoid molecule's production. When you bake cookies, you use a recipe. The DNA contained in the genes is the recipe for flavonoids. The genes for flavonoid production say what ingredients to use, when to add them, what type of enzyme, and when to use it to catalyze the process. These recipes are refined through generations. Just like your grandmother might have a good cookie recipe that everyone in the family uses, the genetic recipe for flavonoid production is refined by evolution through natural selection. The flavonoids produced and process to make them are those that are generally adaptive for the plant to survive in a particular environment.

Humans can change gene expression through direct modification to genes or selective breeding. Selective breeding might involve only allowing certain individuals with the desired colors to reproduce with each other or only letting the plants reproduce asexually (this means that there is only one parent and that one individual contributes genetic information to the offspring). Changing gene expression involves identifying and targeting genes. The researchers Courtney-Gutterson et al. 1994 (1) altered gene expression in a chrysanthemum and specifically suppressed an enzyme that catalyzes a reaction in flavonoid production. By doing so, they were able to cultivate white varieties of a usually pink flower. Techniques like this allow for the beautiful bouquets you find in the store. The pictures below show an example of a modified and a wild rose.

File:Blue Rose APPLAUSE.jpg File:Cherokee rose.jpg

 Left: Hybrid rose Suntory “Blue Rose” developed by genetically modifying a white rose to produce and use blue pigment (3); Right: Cherokee Rose, a ‘wild’ rose.  Both photographs public domain.

Beyond color, plants and humans benefit from flavonoids in other ways. Plants use flavonoids for communication with symbiotic microbes that live in their roots. Plants also use flavonoids for protection from UV (they need "sunscreen" too!). Stilbenes, a type of compound similar to the flavonoids, are made by several groups of plants including grapes. These stilbenes may contribute to human health and are responsible for the heart-healthy aspects of red wine (2). So, go pick out a bouquet, find a bottle of red, grab some grapes and a cheeseboard, and celebrate those flavonoid-producing flowers -- they deserve it!

  1. Courtney-Gutterson, Neal, et al. "Modification of flower color in florist's chrysanthemum: production of a white–flowering variety through molecular genetics." Nature Biotechnology 12.3 (1994): 268-271.
  2. Winkel-Shirley, Brenda. Flavonoid Biosynthesis. A Colorful Model for Genetics, Biochemistry, Cell Biology, and Biotechnology. Plant physiology 126 (2001):485-493.