Transcriptome analysis of gene expression during the hydrotropic response in Arabidopsis seedlings

Because of their sessile nature, plants require appropriate strategies to adapt to the surrounding environment. Tropism is a directional growth in response to environmental stimulus that allows plants to adapt to changes in sunlight, nutrients and water. Plant roots display hydrotropism in response to a moisture gradient, and this phenomenon is believed to play an important role in the ability of the plant to obtain water. However, the molecular mechanism underlying hydrotropism has yet to be fully elucidated. To investigate the transcriptional changes associated with root hydrotropism, we performed a whole-genome microarray analysis of Arabidopsis to monitor the transcription levels of 22,810 genes during the early phase of the hydrotropic response. The transcript levels of 793 genes were significantly changed 1 or 2 hours (h) after hydrotropic stimulation. A large number of genes responsive to abscisic acid (ABA) or water-stress were among the hydrostimulation-responsive genes. In contrast, there appeared to be little overlap in transcript abundance between hydrostimulation-responsive and gravistimulation-responsive genes. Our results suggest that ABA and water-stress responses are important signal transduction mechanisms involved in the root hydrotropic response, and that the signaling pathways involved in hydrotropism differ from those of gravitropism.