Poster: Photomorphogenesis
Abs #
508: In search of central downstream signaling elements important to light-regulated stem growth
Studying the kinetics of light-regulated stem growth in photomorphogenic mutants of Arabidopsis through the use of computerized CCD imaging has helped us to better envision the roles played here by the phytochromes (PNAS 96: 14142-14146) and certain downstream signaling elements, particularly SPA1 (Plant Physiol 126: 1291-1298). A central feature of this work is the developing view that light-controlled seedling growth actually occurs as a dynamic balance of light-dependent growth inhibitive and promotive processes (Curr Opin Plant Biol 4: 436-440). Building upon the hypothesis that SPA1 is a nuclear-localized transcription factor that detectably promotes growth after 2 h of red-light irradiation, we performed a tightly-defined genome-wide analysis of expression using an Arabidopsis microarray in an attempt to identify gene products that are central to growth regulation through SPA1 action. We probed arrays with labeled cRNA synthesized from mRNA isolated from duplicate dark-grown and 3-h red-light-treated populations of both wild-type and SPA1-null seedlings. This analysis identified a small sample of genes that are regulated differently in red light between wild type and spa1 mutants. One such gene with a clear role in cell expansion (i.e. growth) is Expansin 8 (EXP8). We are currently using RT-PCR as a means to verify the results of our genome survey. We are also using this technique to test the hypothesis that EXP8 is a central element in light-regulated growth by establishing whether its levels are differentially regulated by other phytochrome downstream signaling factors such as FHY1 and FHY3. These data and our ongoing progress will be discussed.
