Transcript profiling II: Gene expression data
Numerous lines of evidence implicate local phytohormone imbalances at the site of giant cell induction, and root-knot nematode produces biologically-active cytokinin. We have used the 8,200 gene Affimetrix Arabidopsis array to establish global benchmark expression profiles following application of exogenous cytokinin. Seven-day-old Arabidopsis seedlings grown under 24hr light were treated with cytokinin (5µM BA) for either 15min, 45 min, 2hr, 8hr or 24hr. Expression levels within a chip were normalized to the median expression value on that chip and then further normalized to a chip for which plants were grown under identical conditions, but treated with the vehicle (DMSO) only.
Genes have been grouped based on deduced function. Importantly, the cytokinin response genes (ARRs) previously shown to be cytokinin inducible were found to be up-regulated in our experiments; several cytokinin biosynthesis-related genes also were induced. Interestingly, several auxin related genes were also induced along with various other known and unknown genes, including kinases and transcription factors. Many fewer genes appear to be down-regulated by cytokinin, although this pattern was exhibited by a small group of peroxidases.
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To better view the expression profiles, genes have been grouped based on their expression pattern by a K-means cluster analysis. All the genes in these graphs had at least a 2-fold increase in the ratio of gene expression with cytokinin treatment over DMSO at three separate time points.
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