Characterization of early induced genes in Arabidopsis thaliana responding to bacterial inoculation: identification of centrin and of a novel protein with two regions related to kinase domains.

The early response to bacterial inoculation has been investigated and two Arabidopsis genes, ap3.3a and ap4.3a have been characterized. The AP3.3A protein showed high identity to centrin, a ubiquitous cytoskeletal protein first identified in unicellular green alga. Amino-acid sequence analyses of the AP4.3A protein indicates that the second gene characterized encodes an unusual protein with two putative kinase domains. Expression of ap3.3a and ap4.3a was rapidly induced after pathogen inoculation. A role of ap3.3a in plant defense could be postulated based on its preferential induction during the incompatible interactions analyzed. In contrast, activation of ap4.3a was not specific and could be related to a more general stress response.