Mechanisms of response to fluctuating shade

CASAL, JORGE JOSÉ

Simposio; The 2011 International Symposium on Plant Photobiology (ISPP); 2011

The light signalling circuitry is complex, with many molecular components involved in apparently redundant functions. Our working hypothesis is that the complexity of the light signalling network is a consequence of the complex environment plants have to face and the divergent physiological processes under light control.  While most studies have used seedlings exposed to contrasting but constant light treatments, the natural light environment may exhibit strong daily fluctuations. The reduced irradiance and altered spectral composition of shade-light promote stem growth compared to unfiltered sunlight. However, due to gaps in the canopy, plants shaded by neighbours often experience sunflecks, i.e. brief periods of exposure to unfiltered sunlight.  We will show that sunflecks are perceived by phytochromes A and B and inhibit hypocotyl growth in Arabidopsis thaliana mainly if they occur during the final portion of the photoperiod. By using forward and reverse genetic approaches we found that ELONGATED HYPOCOTYL 5, LATE ELONGATED HYPOCOTYL, PHYTOCHROME KINASE SUBSTRATE 4 and auxin signalling are key players in this response. The response to sunflecks provides an example, where selected molecular components become important under a specific environment.