Poster: Tropisms

Abs # 401: Characterization of InsP₃-mediated transcriptional changes in response to gravistimulation.

Presenter:	Winter Sederoff, Heike , heike_winter@ncsu.edu
Authors	Winter Sederoff, Heike  (A)   Salinas-Mondragon, Raul  (A)   Hung, Chui-Yueh  (A)   Brown, Christopher S (B)   Boss, Wendy F (A)   Perera, Imara Y. (A)
Affiliations:	(A): Dept. Botany, North Carolina State University (B): Kenan Institute, North Carolina State University

As an approach towards further delineating the role of inositol 1,4,5 trisphosphate (InsP₃), in plant gravitropism, we have analyzed time-resolved transcript profiles of gravistimulated transgenic Arabidopsis plants constitutively expressing the human type I inositol polyphosphate 5-phosphatase (InsP 5-ptase), an enzyme that specifically hydrolyzes InsP₃. Even though the transgenic plants have no obvious phenotype under normal growth conditions, the gravitropic bending response of the roots of transgenic seedlings are reduced by ~ 30% compared to the wild type. Microarray analysis of the root tips reveals significant differences in the abundance of about 8% of all transcripts in vertical (control) root tips of InsP 5-ptase plants compared to wildtype plants. Upon gravistimulation, transcriptional regulation occurred within 2 min. Comparison of transcript profiles during the first hour of gravistimulation revealed further differences between the transgenic and wild type plants. Several genes showed the same pattern of changes in transcript abundance in both transgenic and wildtype root tips. Expression of those genes is probably independent of the InsP₃-signalling pathway. Some clusters of genes however were specifically regulated only in either the wildtype or the transgenic plants after reorientation. The clusters of genes that are induced only in the wild type plants in response to gravistimulation, are likely to be downstream targets of the InsP3-mediated signaling pathway. The changes in transcript profiles of the InsP 5-ptase transgenic plants which show an altered gravitropic response will help delineate the contribution of InsP₃ to the gravitropic signal transduction cascade and its potential integration with other tropic responses. (Funded by NASA).