Plants in the cabbage family didn’t intend to be so tasty. The taste is part of a defence against herbivores. Now scientists in Japan have found the genes for this defence are repurposed genes that originally controlled stomata, the pores in leaves that plants “breathe” through.
Opening and closing of stomata for gas exchange depends on guard cells that guard the holes in a leaf. They’re very different to myrosin cells, the cells that help create the chemical defences against herbivores. Yet they share a master regulator gene called FAMA which controls their development.
If you poison someone feeding on you, you don’t want to poison yourself in the process. Myrosin cells produce a chemical called myrosinase. These cells are near sulphur rich cells. When a herbivore attacks, the chemicals get mixed so the poison is only in the plant when it’s needed.
Shirakawa and colleagues identified a gene called WASABI MAKER (WSB) that’s directly activated by FAMA and is the essential trigger for myrosin cell development. Plants without WSB completely failed to form these defence cells, making WSB a key link in a genetic cascade to make these cells.
The FAMA protein was already known from experiments on the model plant Arabidopsis thaliana, where it was found to regulate gene expression for gas exchange. So it appears that the genes that help regulate defence are in part repurposed from genes involved in respiration.
A clue to WSB’s origin as a stomata gene is found in plants where it is missing. It is found across flowering plants on the land, but not in marine plants, such as seagrasses. Zostera marina doesn’t have stomata and it has lost genes connected with stomata, as well as WSB.
WSB controls the development of myrosin cells through another gene called CCS52A1. WSB can switch on CCS52A1, and then CCS52A1 causes the myrosin cells to experience endoreplication, so the cell replicates its DNA multiple times without dividing, causing it to grow much larger.
“This discovery is particularly interesting because it highlights how gene repurposing allows plants to develop new survival strategies without evolving entirely new genes,” says co-author Toshiro Ito in a press release.
“Beyond offering new insights for crop improvement strategies, we believe our future work will help answer one of biology’s most fundamental questions: How have plants achieved such remarkable diversity with a limited number of genes?” adds Dr. Shirakawa.
The research has important agricultural implications. Since FAMA regulates both gas exchange (through stomata) and defence (through myrosin cells), it shows breeding for certain traits, such as increased gas exchange efficiency could also have knock-on effects elsewhere, such as defence.
However, it also shows that there may be opportunities to get a double-win by improving how plants use FAMA. Better FAMA genes could lead to more efficient stomata in a warming climate AND improve resistance to invasive pests that are also migrating with the changing temperatures.
Shirakawa, M., et al. (2025). Co-option and neofunctionalization of stomatal executors for defence against herbivores in Brassicales. Nature Plants, 11, 483-504. https://doi.org/g897b6 (FREE)
Cross-posted to Bluesky & Mastodon.
Image: Canva.
Related