Origins of strigolactone and karrikin signaling in plants
Wang Q, Smith SM and Huang J
Trends in Plant Science
Strigolactones (SLs) are not only phytohormones that play multiple roles in plant growth and development, but also rhizosphere signals for communication between plants and microbes.
Karrikins (KARs) are exogenous compounds generated from burning vegetation which can stimulate seed germination. They contain a butenolide moiety similar to that of SLs.
The KAR receptor KAI2 is believed to normally recognize endogenous karrikin-like compounds referred to as KAI2-ligands (KLs). The KAI2 signaling pathway influences various developmental and physiological processes in plants.
The duplication and differentiation of KAI2 in seed plants led to the evolution of the SL receptor gene family D14.
The perception and signaling of KLs by KAI2 is commonly considered to be a major innovation during the early evolution of land plants, but the origin of KAI2 and SL/KL signaling system is unclear.