Abstract
In tobacco, two mitogen-activated protein kinases (MAPKs), WIPK and SIPK, have been implicated in defense responses to pathogen infection and wounding. WIPK is activated enzymatically in response to these stresses. However, 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 (11E,13E)-labda-11,13-diene-8&alpha,15-diol, designated WAF-1 (WIPK-activating factor1). At nanomolar levels, WAF-1 activated WIPK as well as SIPK and enhanced the accumulation of transcripts of wound- and pathogen-inducible PR genes. Quantitative analysis of endogenous WAF-1 revealed that levels increased rapidly in leaves during a hypersensitive response to TMV and after wounding. Furthermore, treatment of leaves with WAF-1 resulted in enhanced resistance to TMV infection. These results suggest that WAF-1 functions as an endogenous signal mediating defense responses of tobacco plants to TMV infection and wounding. We also describe about a new MAPK that is involved in wound signaling.
