Poster: Plant-pathogen interactions

Abs # 500: LeMPK3 is a MAP kinase with dual specificity induced during tomato defense and wounding responses

Presenter:	Mayrose, Maya , mayag@post.tau.ac.il
Authors	Mayrose, Maya  (A)   Bonshtien, Arale  (A)   Sessa, Guido  (A)
Affiliations:	(A): Tel-Aviv University

MAPK cascades are readily activated during the plants response to avirulent pathogens or to pathogen-derived elicitors. We show that expression of the tomato MAPK LeMPK3 is specifically induced during elicitation of hypersensitive response in resistant plants infected by the avirulent phytopathogenic bacteria Xanthomonas campestris pv. vesicatoria and Pseudomonas syringae pv. tomato, as well as upon treatment with the fungal elicitor EIX. LeMPK3 gene expression was also induced very rapidly by mechanical stress and wounding much earlier than upon pathogen infection, but not in response to the defense-related plant hormones ethylene and jasmonic acid. Moreover, in resistant tomato plants infected by Xanthomonas campestris pv. vesicatoria, transcript accumulation was followed by an increase in LeMPK3 kinase activity. Biochemical characterization of a GST-LeMPK3 fusion protein revealed that the LeMPK3 MAPK autophosphorylates in vitro mainly on tyrosine and less so on threonine and serine, while it phosphorylates myelin basic protein on serine and threonine. In vitro phosphorylation of a poly(Glu,Tyr) copolymer by LeMPK3 demonstrated its capability to phosphorylate tyrosine residues on substrates as well. By mutagenesis and phosphoamino acid analysis, Tyr201 in the kinase activation domain was identified as the main LeMPK3 autophosphorylation site and as critical for kinase activity. Finally, LeMPK3 autophosphorylation showed a preference for Mn²⁺ cations, and proceeded via an intramolecular mechanism with an estimated K_m value for ATP of 9.5 uM. These results define LeMPK3 as a MAP kinase with dual specificity and strongly suggest that it represents a convergence point for different signaling pathways inducing the activation of defense responses in tomato.