Molekulare Funktionsanalyse von Signaltransduktionssystemen in Arabidopsis thaliana

Abstract

One of the analyzed signal transduction systems mediates the specific transmission of calcium signals. One type of calcium sensors are the AtCBL (Calcineurin B-like) protein family comprising of ten members in Arabidopsis thaliana. These AtCBLs interact with a protein kinase family of 25 members, the AtCIPKs (CBL-interacting protein kinases). The proteins of both families interact in a yeast two-hybrid system in a specific manner. A 24 amino acid domain has been identified to be required and sufficient for the interaction. Factors generating specificity in this system are specific complex formation and the different expression and localizations of the CBLs and CIPKs within the cell as well as within the plant. Those calcium signals are known to be generated in response to environmental and biotic stimuli. Analyzing T-DNA insertion mutants with insertions in the CBL1 gene and in the CIPK1 gene lead to the identification that the cbl1 mutant as well as the cipk1 mutant render plants more sensitive to drought and heat. AtCBL1 seems to be a general calcium sensor involved in different pathways. The type B response regulator ARR2 is also involved in stress responses. Loss of ARR2 by an insertion of a Ds-transposon leads to pleiotropic effects in the anatomy in growth and structure of the flowers as well as in physiological changes. This mutant demonstrates a higher resistance to drought and salt in contrast to its corresponding wildtype. Analyzing the arr2 mutant leads to the identification of a new ethylene signal transduction pathway. In cooperation with the group of Klaus Harter in Freiburg insensitivity of the mutant to the plant hormones ethylene and cytokinine has been observed. This observation pointed to the pathways in which the ARR2 protein may be involved. In three-hybrid analysis an interaction via the histidin transfer protein AHP2 with the ethylene receptor ETR1 was established. Starting from this receptor a phosphorelay starts ending on the ARR2 protein.