RSF1, an Arabidopsis locus implicated in phytochrome A signaling

In Arabidopsis, phytochrome A (phyA) is the major photoreceptor both for hi gh irradiance responses to far-red light and broad spectrum very low fluenc e responses, but little is known of its signaling pathway(s). rsf1 was isol ated as a recessive mutant with reduced sensitivity to far-red inhibition o f hypocotyl elongation. At the seedling stage rsf1 mutants are affected, to various degrees, in all described phyA-mediated responses. However, in adu lt rsf1 plants, the photoperiodic flowering response is normal. The rsf1 mu tant has wild-type levels of phyA suggesting that RSF1 is required for phyA signaling rather than phyA stability or biosynthesis. RSF1 thus appears to be a major phyA signaling component in seedlings, but not in adult, Arabid opsis plants.