Background: Recognition of pathogenic microorganisms triggers in plants comprehensive transcriptional reprogramming. In order to identify transcriptome-level control elements required for plant immune responses we are examining several sets of genes found by microarray experiments to be co-activated in Arabidopsis thaliana (Arabidopsis) seedlings infected with the oomycete Hyaloperonospora parasitica. Promoter motifs conserved in clusters of co-expressed genes may be involved in mediating coordinated gene activity patterns. Although numerous studies identified such conserved promoter motifs in co-expressed gene sets, reports confirming their function as regulatory elements are rare. Results: FORC A is a hexameric promoter motif that is conserved in clusters of Arabidopsis genes co-expressed in response to fungal or oomycete pathogens as well as defined light treatments. FORC A is generally more frequently present in Arabidopsis promoter regions than statistically expected. It constitutively interacts in a DNA-sequence specific manner with nuclear Arabidopsis proteins. These interactions are suppressed by defense-related stimuli and enhanced by prolonged exposure to constant light. Furthermore FORC A mediates constitutive reporter gene expression in transiently transformed Nicotiana benthamiana leaves as well as in stably transformed Arabidopsis plants. Its responsiveness to defense-stimuli is modulated by the duration of light exposure. In plants grown under normal light conditions or constant darkness defense-related stimuli result in suppression of FORC A-mediated reporter gene expression, while in plants grown under constant light exposure, defense-induction results in enhanced FORC A-mediated expression. In addition, we found plants subjected to constant light exposure to exhibit reduced susceptibility to virulent H. parasitica. Conclusion: We propose that FORC A is a regulatory cis-element that is present in a wide variety of Arabidopsis promoters. It integrates light- and defense-related signals and participates in adjusting the transcriptome to changes in environmental conditions.
Evrard, A., Ndatimana, T., & Eulgem, T. (2009). FORCA, a promoter element that responds to crosstalk between defense and light signaling. BMC Plant Biology, 9. https://doi.org/10.1186/1471-2229-9-2