The karrikin 'calisthenics': Can compounds derived from smoke help in stress tolerance?

Karrikins (KARs) are unique butenolides derived as a by-product of incomplete combustion during wildfire. Some receptive plant species respond to KARs in the form of accelerated germination. These molecules originate from stress to mediate tolerance against different sub-optimal conditions like oxidative stress, drought and low-light intensity (shade stress). KARs promote seed germination, seedling establishment and ecological diversity by accelerating the abundance of selective communities of plants. The signaling pathway is closely related, yet unique from strigolactones (SLs). Due to the structural relatedness with SLs, KARs have potential roles in mediating abiotic stress tolerance in plants. In addition, the KAR directly/indirectly interact with crucial phytohormones like abscisic acid, gibberellic acid, auxins and ethylene. This article is a summarized update on KAR research in recent times. The exhaustive discussions would be beneficial for understanding the extraordinary strategy devised by nature to protect plants from stress using a molecule which is itself generated out of stress.