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Positive phototropism in roots: who is involved?  M.L. Molas¹, Correll MJ², Kiss JZ (1) Dept. of Botany, Miami University, Oxford. OH 45056 (2) Dept. of Agricultural and Biological Engineering, University of Florida, Gainesville. FL 32611-0570

   Red light, acting through the phytochromes, controls numerous aspects of plant development. Previously, we had identified a positive phototropism in roots induced by red light, which is mediated by PHYA and PHYB. To investigate the set of genes involved in this novel phototropic response, we performed gene profiling studies using cDNA microarrays and quantitative Real-Time PCR in roots of Arabidopsis seedlings exposed to 1 h of red light. Some of the genes found to be differentially expressed in this study were PHYTOCHROME KINASE 1 (PKS1), LONG HYPOCOTYL 5 (HY5), EARLY FLOWERING 4 (ELF4), and GIGANTEA (GI), all significantly upregulated in roots of seedlings exposed to 1 h of red light. In addition, the upregulation of SUPPRESSOR OF PHYTOCHROME A RESPONSES 1 (SPA1) and CONSTITUTIVE PHOTOMORPHOGENIC 1-like (COP1-like) genes suggests that the PHYA-mediated pathway was attenuated by red light. Interestingly, members of the RPT2/NPH3 (ROOT PHOTOTROPIC 2/NON PHOTOTROPIC HYPOCOTYL 3) family, which have been shown to mediate blue-light-induced phototropism, also were differentially regulated in roots in red light. Therefore, these results suggest that red and blue light pathways interact in roots. Currently, experiments are in progress testing rpt2, hy5 and pks1 mutants to investigate their involvement in positive phototropism in roots induced by red light. These studies utilize a computer-based feedback system to obtain high resolution data on this response in the mutants compared to the response in the wild type.

(Supported by Miami University DUOS program and NASA grant NCC 2-1200)