Identification of direct targets of the Arabidopsis transciption factor GLABRA3 (GL3)

To understand the complex network of the biological processes of an organism, transcription factors (TFs) and their direct target genes must be identified. In Arabidopsis, the TF GLABRA3 (GL3) is involved in trichome initiation and development. To identify the direct target genes of GL3, an inducible activation system coupled with microarray analysis was performed. To this end, two week old Arabidopsis seedling plants expressing the GL3-GR (glucocorticoid receptor) fusion protein with a native promoter (pGL3) were treated for two hours with dexamethasone alone (DEX), dexamethasone + cycloheximide (DEX +CHX), cycloheximide (CHX) and mock solution (M). Ten genes were selected as candidate genes in DEX and DEX +CHX (in relation to Mock and CHX) respectively and validated by real-time RT-PCR. The results showed that the ten genes were not up-regulated greater than two-fold and the induction of these genes did not occur rapidly after the two hour treatment in the pGL3::GL3-GR plants, indicating these candidate genes may in fact be indirect targets. Gene Ontology analysis of the candidate genes revealed that the GL3 pathway have involvement in biological processes related to abiotic or biotic stress, signal transduction, transcription, and transport. These target genes suggest that GL3 is associated with other TFs and proteins in combinatorial manner. Keywords Arabidopsis, GL3, trichomes, transcription factor, microarray, real-time RT-PCR