Abstract
Activation of wound-induced protein kinase (WIPK), one of the most characterized plant MAPKs, has been implicated in defense responses in tobacco. Despite the important role of WIPK in defense signaling, no endogenous signal responsible for the activation has been identified. We isolated a WIPK-activating substance from TMV-infected tobacco leaves and identified it as a novel labdane-type diterpene. This substance (WAF-1) activated WIPK at nanomolar concentrations.
Quantitative analyses of endogenous WAF-1 revealed that levels increased rapidly in leaves during a hypersensitive response to TMV and after wounding. Exogenously supplied WAF-1 enhanced accumulation of transcripts of defense-related genes. These reuslts suggest that WAF-1 functions as an endogenous signal which activates WIPK and defense-related genes in tobacco.
