Karrikins

Karrikins (Kks) are plant smoke derivatives that regulate plant growth by mimicking stringolactone (SL) signaling hormones. Kks are released in huge quantities into the air post bushfires or wildfires, and upon settling down, they stimulate seed germination (SG), seedling vigor (SV), senescence of leaves, development of axillary meristems through signal transduction (ST) pathways involving F-box protein, and SMAX1 (Suppressor of more axillary growth-1). Kks also follow a pattern similar to SLs in the inhibition of root branching and stem thickening by interacting with KAI2 (Kk-insensitive2) via KAI1, which subsequently causes seed-germination inhibition and hypocotyl elongation. Not only does the Kk family mediate plant development but it also affects the expression of genes involved in quorum sensing (QS). The structural similarity between some QS molecules and Kks is exploited by plant systems to manipulate several bacteria to protect against pathogens by repressing virulence factors. This chapter digs deep into the signaling network of Kks in several plant parts for their potential role in plant development and plant growth including SD, SV, and stress tolerance, besides highlighting their potential utility in future research.