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Plant Physiology Preview Published on May 3, 2007; 10.1104/pp.107.101063
Received April 13, 2007 The Tomato MAP Kinases LeMPK1, -2 and -3 are Activated during the Cf-4/Avr4-Induced HR and Have Distinct Phosphorylation Specificities
Laboratory of Phytopathology, Wageningen University, Wageningen, The Netherlands; Department of Biological Sciences, University of South Carolina, Columbia, U.S.A * Corresponding author; email: Matthieu.Joosten{at}wur.nl.
Tomato (Solanum lycopersicum, further referred to as Lycopersicon esculentum) plants with the Cf-4 resistance gene recognize strains of the pathogenic fungus Cladosporium fulvum that secrete the avirulence protein Avr4. Transgenic tomato seedlings co-expressing Cf-4 and Avr4 mount a hypersensitive response (HR) at 20°C, which is suppressed at 33°C. Within 120 minutes after a shift from 33°C to 20°C, L. esculentum MAP kinase (LeMPK) activity increases in the Cf-4/Avr4 seedlings. Searching tomato genome databases revealed at least 16 LeMPK sequences, including the sequence of LeMPK1, -2 and -3 that cluster with biotic stress-related MAPK orthologues from Arabidopsis (Arabidopsis thaliana) and Nicotiana tabacum. LeMPK1, -2 and -3 are simultaneously activated in the Cf-4/Avr4 seedlings and to reveal whether they are functionally redundant or not, recombinant LeMPKs were incubated on PepChip Kinomics® slides carrying peptides with potential phosphorylation sites. Phosphorylated peptides and motifs present in them discriminated between the phosphorylation specificities of LeMPK1, -2 and -3. LeMPK1, -2 or -3 activity was specifically suppressed in Cf-4-tomato by virus-induced gene silencing and leaflets were either injected with Avr4 or challenged with C. fulvum secreting Avr4. Interestingly, LeMPK1 and -3 appear to play a role in the resistance response to C. fulvum whereas LeMPK2, and also LeMPK3, are required for HR. These results indicate that the LeMPKs play different and also overlapping roles in the HR and resistance upon recognition of an avirulent pathogen.
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