A CHLORATE-RESISTANT MUTANT DEFECTIVE IN THE REGULATION OF NITRATE REDUCTASE GENE-EXPRESSION IN ARABIDOPSIS DEFINES A NEW HY LOCUS

Light acts both directly as a signal and indirectly through photosynth esis to regulate the expression of genes encoding nitrate reductase (N R). Here, we report the isolation and characterization of a novel chlo rate-resistant mutant that is defective in the regulation of NR gene e xpression. The response of NR2, but not NR1 or the gene encoding nitri te reductase (NIR), to light signals was impaired in this Arabidopsis mutant, designated cr88. In addition to NR2, the light regulation of t he genes encoding the chlorophyll alb binding protein (CAB) and the sm all subunit of ribulose bisphosphate carboxylase (RBCS) was also impai red in this mutant. These results suggest that the pathway through whi ch light regulates the expression of NR2, CAB, and RBCS genes is diffe rent from those that regulate the expression of NR1 and NiR. An examin ation of the deetiolation process under different light spectra showed that cr88 is defective in red light-mediated deetiolation. Complement ation tests with various long hypocotyl (hy) mutants indicated that CR 88 identifies a new HY locus. The possible functions of CR88 are discu ssed.