The objective of this work is to add new core components to the model of the circadian system. Biological processes exhibiting an approximate 24-hour periodicity that persist in the absence of environmental cues are found in organisms spanning all major kingdoms of life. In higher plants, surprisingly little is known about the core oscillator and few molecular mechanisms have been revealed. The key clock-associated factor TOC1, which has a crucial function in the integration of light signals to control circadian and morphogenic responses, was identified from a screen for abnormal period length in a mutagenized accession of Arabidopsis expressing a circadian regulated CAB2::Iuc reporter gene. This study will recover mutants from a population of mutagenized plants expressing TOC1:luc. Mutant alleles will be rapidly identified by high-density oligonucleotide array genotyping. Simultaneously, a battery of established photomorphogenic, transcriptional and biochemical tests will help establish the role of each new gene in the circadian system. The continued elucidation of the temporal control mechanisms in Arabidopsis will complement similar analyses in other models, ultimately significantly impacting our understanding and treatment of human circadian disorders. In addition, this work will contribute to the understanding of many other plant-specific processes, such as floral development and photoregulation of growth and metabolism. [unreadable] [unreadable]