Control of Circadian Rhythms and Photoperiodic Flowering by the Arabidopsis GIGANTEA Gene

Photoperiodic responses in plants include flowering that is day-length–dependent. Mutations in the Arabidopsis thaliana GIGANTEA ( GI ) gene cause photoperiod-insensitive flowering and alteration of circadian rhythms. The GI gene encodes a protein containing six putative transmembrane domains. Circadian expression patterns of the GI gene and the clock-associated genes, LHY and CCA1 , are altered in gi mutants, showing that GI is required for maintaining circadian amplitude and appropriate period length of these genes. The gi-1 mutation also affects light signaling to the clock, which suggests that GI participates in a feedback loop of the plant circadian system.