Karrikin Insensitive 2 (KAI2) (KAI2)

Karrikin Insensitive 2 (KAI2), also known as Hyposensitive to Light (HTL), is an alpha/beta-hydrolase fold protein that functions as a receptor in plants for perceiving karrikins—smoke-derived molecules that stimulate germination—and an unidentified endogenous signal known as KAI2-ligand (KL) (Waters et al., 2012, Nature). Upon ligand binding, KAI2 undergoes a conformational change that allows it to interact with the F-box protein MAX2, which subsequently targets SMAX1 and SMXL2 suppressor proteins for proteasomal degradation (Morffy et al., 2016, Plant Physiology). This signaling pathway is essential for regulating various aspects of plant development, including seed germination, seedling photomorphogenesis, and root hair growth. In parasitic plants such as Striga hermonthica, the KAI2/HTL gene family has expanded and evolved to detect host-derived strigolactones, making these receptors primary targets for controlling agricultural infestations (Conn et al., 2015, Science). While KAI2 is not a human therapeutic target, it is a significant focus for the development of next-generation agrochemicals and synthetic growth regulators aimed at enhancing crop resilience and managing parasitic weeds (Bürger & Chory, 2020, Trends in Plant Science). The receptor's dual function as both a hydrolase and a signaling scaffold presents unique opportunities for chemical intervention in plant development.

Other names

Hyposensitive to LightHTLD14-likeKAI2-likeD14L

Ligand-induced recruitment of the MAX2 F-box protein to the KAI2 receptor, leading to the ubiquitination and proteasomal degradation of SMAX1 and SMXL2 suppressor proteins (Waters et al., 2012; Morffy et al., 2016).