TRANSCRIPTIONAL PROFILING OF THE gps1 MUTANT OF ARABIDOPSIS

Gravity is the fundamental stimulus governing plant growth and stimulus. Normally, plant shoots bend up in response to gravistimulation. However, if plants are put on their side at 4°C this response is not seen. If returned to room temperature they bend in the response to gravity stimulus received in the cold (gravity persistent signal or GPS response). Utilizing this GPS response screen, the gps (gravity persistent signal) 1 mutant in Arabidopsis was isolated. gps1 fails to bend when gravistimulated at 4°C and returned to vertical at room temperature. This study involves the transcription profiling of the gps1 mutant at two time points. Wild-type and gps1 were gravistimulated at 4°C, and the inflorescence tissue in the region of elongation was collected 5 minutes after returned to vertical at room temperature. As a cold control both the wild-type and gps1 plants were also kept vertical at 4°C, and the inflorescence stem tissue was collected 5 minutes after returned to room temperature. RNA was extracted from these samples and used to make the target population for hybridization to Affymetrix ATH1 Arabidopsis gene chips. A list of differentially expressed genes in the mutant when compared to the wild-type was obtained after the analysis of the data. Quantitative RT-PCR was performed on the genes selected from the differential expression list of the microarray data. The experimental design included two different treatments: the cold gravistimulation of gps1 and wild-type with RNA extraction at 0min, 30min, 60min and 70min; and the cold gravistimulation and coldtreatment without gravistimulation of WS wild-type with RNA extraction at 0min, 30min, 60min and 70min. Two biological replicates were used for each gene for each treatment with two technical replicates for each biological replicate. A Cytochrome P450, F box protein, Constans B box Zinc finger family protein and bZIP family transcription factor increased more than 2 fold in the gps1 mutant after 60 minutes.