Karrikin

[1][2] Karrikins help stimulate seed germination and plant development because they mimic a signaling hormone known as strigolactone.

Burning plant products, such as straw, filter paper, cigarettes, and some sugars, can also produce karrikins.

[1] The first karrikin discovered, abbreviated as KAR1, was initially named gavinone in reference to its discovery by chemist Gavin Flematti.

After consulting with an etymologist, Flematti proposed changing the name of the molecule and its related compounds to karrikin.

They thrive because the fire removes competing vegetation and provides nutrients and light for the emerging seedlings.

Plants in many families respond to smoke and karrikins, suggesting that this response has evolved independently in different groups.

Seeds from a number of different flowering families like tomatoes, lettuce, and trees respond to karrikin signaling.

[16] The KAI2 protein has a catalytic triad of amino acids which is essential for activity, consistent with the hypothesis that KAI2 hydrolyses its ligand.

This interaction targets the ubiquitination and destruction of proteins which are responsible for different aspect of plant growth, like the outgrowth of lateral shoots.

This means that strigolactones, upon their interaction with D3 and D14; ubiquinate, and destroy proteins like DWARF53, which are responsible for the outgrowth of lateral shoots, and for the inhibition of stem thickening and root branching.

[26] In Arabidopsis, karrikins work in a similar way to strigolactones; they require homologous proteins known as KARRIKIN-INSENSITIVE1 (KAI1 or MAX2) in order to be able to interact with KARRIKIN-INSENSITIVE2 which is responsible for hypocotyl elongation and the inhibition of seed germination.

[29] In Arabidopsis, karrikins influence seedling photomorphogenesis, resulting in shorter hypocotyls and larger cotyledons.

The KAI2 protein is also required for leaf development, implying that karrikins could influence other aspects of plant growth.

Karrikin signaling could have evolved with seed plants as a result of the divergence of KAI2 and DWARF14 functions, possibly during the Cretaceous period when fires were common on Earth.