infestans and boeh merin from P. boehmeriae in tobacco, flg22 from flagellated bacteria and elf18 from the elongation factor Tu in Arabidopsis seedlings. Here we describe an A. thaliana mutant which fails to induce cyt elevation in Arabidopsis roots in response to protein inhibitors the exudate preparations from pathogenic root interacting microbes. The chemical components which in duce cyt elevation are either present in cell wall preparations from these microbes or released into the medium from mycelia or germinating spores. Although these chemical mediators have not yet been determined, the shape of their Ca2 signatures, their dose dependency and refractory nature demonstrate that they Inhibitors,Modulators,Libraries require CYCAM1 for function. The cycam1 mutant is not impaired in the response to flg22 and to a CWE from the root colonizing fungus M.

hyalina, indicating Inhibitors,Modulators,Libraries some specificity of Arabidopsis response to pathogen exudates. Like flg22 and the Myc factor, the active com ponents in the A. brassicae exudate preparations are thermostable, hydrophilic, polar and of low molecular weight. Interestingly, the CWEs, EPM and EPS preparations from A. brassicae induce cyt elevation, but not the typical disease symptoms of the fungus in Arabi dopsis, while the Tox preparation from A. brassicae induces cyt elevation and is toxic. Toxs from pathogenic fungi including A. brassicae are known to disrupt membranes which might also contribute to the Ca2 influx into the cyto plasm. This might also explain the slower recovery of the Ca2 signal after Tox application than after application of CWE, EPM and EPS preparations.

The Ca2 response in duced by the non toxic CWE, EPM or EPS Inhibitors,Modulators,Libraries might establish a first line of defense that is then followed by a second stronger response induced by the Tox. CYCAM1 also plays a role in abiotic stress as demon strated by the increased sensitivity of cycam1 seedlings to ABA, salt and mannitol applications. cyt elevation is well documented in response to drought stress. Both ABA and H2O2 induce cyt elevations in guard cells to regulate stomata aperture. Sustained cyt elevations induced by mannitol are required for tolerance to drought and osmotic stress in Arabidopsis. Inhibitors,Modulators,Libraries Therefore, CYCAM1 is involved in both biotic and abiotic stress responses. It appears that the higher stress sensitivity of cycam1 is associated with imbalances in redox and ROS homeostasis since the mutant accumulates more ROS after A.

brassicae infec tion than the WT. Since this response can also be Inhibitors,Modulators,Libraries induced by the Tox, the pathogen is not required. Several ROS marker genes representative for different selleckchem ROS species are more strongly upregulated in the A. brassicae exposed mutant than in the WT which is consistent with the idea that a gen eral stress response cannot be efficiently repressed in the mutant. A quite strong stimulatory effect by A.