THE PEF MUTANTS OF ARABIDOPSIS-THALIANA DEFINE LESIONS EARLY IN THE PHYTOCHROME SIGNALING PATHWAY

In a screen for early-flowering mutants, a number of mutants that were early flowering under both short and long days were isolated. One suc h mutant, pef1, was selectively insensitive to both red and far-red li ght in the inhibition of hypocotyl elongation response; a classic phyt ochrome phenotype mediated by both PHYA and PHYB. The pef1 mutant seed lings could not be phenotypically rescued by biliverdin, a precursor o f the phytochrome chromophore, nor did they fail to complement any pre viously identified elongated hypocotyl thy) mutants. Difference spectr a and Western blot analysis showed normal concentrations of PHYA photo receptor apoprotein, which appeared photochemically active. It was con cluded that the pef1 mutant is defective in both PHYA- and PHYB-mediat ed signaling pathways, and may represent a lesion in an early step of the phytochrome signal transduction pathway. Additional pef mutants de ficient specifically in PHYB-mediated responses were also identified b y this screen.