Intergration of light signals through an Auxin response factor

This thesis describes an investigation of light perception in plants and in particular, the Shade Avoidance Syndrome (SAS) of responses and their regulation at the genetic level. The SAS responses are of great importance in agriculture, for example in terms of planting density and resource allocation. The research was initiated with a genetic screen of a T-DNA insertional mutant population of the model plant, Arabidopsis thaliana, where specific light conditions were used to isolate candidate genes potentially involved in the fine tuning of plant responses to shaded conditions. A mutant line (N9299) was isolated through this screen. The mutant was subsequently shown to contain a T-DNA inserted in the Auxin Response Factor 18 (ARF18) gene. Phytochrome (PHY) and Phytochromes-interaction factors (PIFs) are the main controllers of the shade avoidance response. This work demonstrates that ARF18 is involved in light perception in plants, calibrating the response to the stimulus and acting as a temporary repressor to allow the accumulation of other molecular players. PIFs can activate the expression of ARF18, allowing a negative feedback mechanism to resolve the specific response to a given light condition. The pleiotropic phenotype of the N9299 mutant has revealed that ARF18 is a key regulator of growth and development, and the work described here has opened new avenues of research into light perception and response mechanisms and other important physiological and morphological processes in plants