When strawberries scream ‘eat me’
I’m a sucker for a bright red strawberry, preferably more than one. I’m seduced by the rich colour, glossy sheen and the promise of the sometimes sweet, sometimes tart flesh. I’ve been known to pick them in secret from my own garden when my daughter isn’t looking, then pretend none were ripe.
Oh, don’t look at me like that. We all have our guilty pleasures. Mine just happens to be Fragaria x ananassa, the garden strawberry.
Of course, humans aren’t the only animals attracted to the red flesh. Birds and small mammals are drawn to them too.
Red strawberries scream ‘go, go, go’ to passing herbivores. I’m ready, come and get me. Swallow me, then poop out my indigestible seeds* far away. Complete my life cycle, disperse my genes.
Now, German scientists publishing in the journal New Phytologist have figured out how a single strawberry gene triggers the pathway to redness and ‘go, go, go’. In particular, they’ve looked at how this happens at just the right time in the strawberry’s development, when its seeds are mature enough.
Although the paper doesn’t say, I’m guessing it’s when the seeds are mature enough to survive the hazardous journey through a bird or mammal gut, out the other end and to germinate when the conditions are right.
The researchers call this process a switch between repulsion and attraction. That’s because strawberries lead a double life, the first part repelling creatures that could harm them, the next attracting ones that can help survive. Colour plays a key part in that switch.
The colour green, which signals immaturity in the strawberry world, characterises the repulsion phase.
That’s when the enzyme anthocyanidin reductase helps strawberries make proanthocyanidins, a class of metabolites that help to protect the developing fruit* from pathogens and pests.
When the seeds are ripe, the gene that produces this enzyme is switched off, signalling the start of the attraction phase. That’s when the biochemical pathway to anthocyanins, which give ripe strawberries their characteristic redness, is set in train.
So, it’s a single gene that I can thank for red strawberries and my guilty pleasure.
*Writing about strawberries can be confusing as the words that botanists use to describe their parts is not how we commonly refer to them, or even how the journal New Phytologist refers to them. I’ve used the words ‘fruit’ to refer to the flesh we eat and ‘seed’ to refer to the little pips on the outside of the ‘fruit’. Botanically speaking, the flesh is not really a fruit but a modified shoot tip, the ‘seeds’ on the outside are the real fruit and are called achenes.