MAP kinase in signal transduction pathways of the plant oxidative burst

Jitae Kim, Purdue University

Abstract

The oxidative burst constitutes one of the most rapid defense responses characterized in the plant kingdom. I have observed that four distinct elicitors of the soybean oxidative burst activate kinases of masses ∼44 kDa and ∼47 kDa. Immunological and biochemical studies reveal that the activated 44 kDa and 47 kDa kinases are MAP kinase family members. To positively identify them, I cloned five different soybean MAP kinases (GMK1 through GMK5) using RT-PCR method. All five MAP kinases contain the conserved TEY phosphorylation sites that are characteristic of MAP kinases. Using a C-terminus specific antibody, the 47 kDa kinase was identified as the GMK1. These data suggest that GMK1 is involved in the signal transduction pathways leading to the oxidative bust. In eukaryotic cells, MAPK isoforms are generally activated by a specific MAPK kinase (MAPKK). To study the MAPK activating pathway leading to the oxidative burst, I cloned three different soybean MAP kinase kinases (GMKK1 through GMKK3). Then, all the GMK1-5 and GMKK1-3 proteins were expressed and purified from E. coli. Interestingly, the recombinant GMKK1 protein could activate both GMK1 and GMK2 in vitro. This result suggests that the activation of GMK1, the soybean MAP kinase involved in the oxidative burst, is mediated by the MAP kinase kinase GMKK1. Based on these and other observations, a preliminary sequence of signaling steps linking elicitor stimulation, kinase activation, and Ca2+ entry, to initiation of oxidant production is proposed.

Degree

Ph.D.

Advisors

Low, Purdue University.

Subject Area

Biochemistry|Botany|Molecular biology

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