Overexpression of LSH1, a member of an uncharacterised gene family, causes enhanced light regulation of seedling development

Light regulates plant growth and development through a network of endogenous factors. By screening Arabidopsis activation-tagged lines, we isolated a dominant mutant (light-dependent short hypocotyls 1-D (Ish1-D)) that showed hypersensitive responses to continuous red (cR), far-red (cFR) and blue (cB) light and cloned the corresponding gene, LSH1. LSH1 encodes a nuclear protein of a novel gene family that has homologues in Arabidopsis and rice. The effects of the Ish1-D mutation were tested in a series of photoreceptor mutant backgrounds. The hypersensitivity to cFR and cB light conferred by Ish1-D was abolished in a phyA null background (phyA-201), and the hypersensitivity to cR and cFR light conferred by Ish1-D was much reduced in the phytochrome- chromophore synthetic mutant, hy1-1 (long hypocotyl 1). These results indicate that LSH1 is functionally dependent on phytochrome to mediate light regulation of seedling development.