title: LAF3, a novel factor required for normal phytochrome A signaling.
abstract: Phytochrome A (phyA) is the photolabile plant light receptor that mediates broad spectrum very low-fluence responses and high irradiance responses to continuous far-red light (FRc). An Arabidopsis mutant laf3-1 (long after far-red 3) was recovered from a screen for transposon-tagged mutants that exhibit reduced inhibition of hypocotyl elongation in FRc. The laf phenotype correlated well with a strongly attenuated disappearance of XTR7 transcript in FRc. The effects of laf3-1 on phyA-controlled CAB, CHS, and PET H expression were more subtle, and the mutation had no clear effects on PET E and ASN1 transcript levels in FRc. The use of two alternative transcription initiation sites in the LAF3 gene generates two isoforms that differ only at their N termini. Transcripts encoding both isoforms were induced during germination and were present at slightly higher levels in de-etiolated seedlings than in those grown in darkness. No significant differential regulation of the two isoforms was observed upon exposure to either FRc or continuous red light. Transcripts encoding the shorter isoform (LAF3ISF2) always appear to be more abundant than those encoding the longer isoform (LAF3ISF1). However, both isoforms were capable of full complementation of the laf3-1 hypocotyl phenotype in FRc. When fused to a yellow fluorescent protein, both isoforms localize to the perinuclear region, suggesting that LAF3 encodes a product that might regulate nucleo-cytoplasmic trafficking of an intermediate(s) involved in phyA signal transduction.
authors.affiliation: Laboratory of Plant Molecular Biology, The Rockefeller University, 1230 York Avenue, New York 10021, USA.
authors.forename: Peter D
authors.initials: PD
authors.lastname: Hare
authors.forename: Simon G
authors.initials: SG
authors.lastname: Moller
authors.forename: Li-Fang
authors.initials: LF
authors.lastname: Huang
authors.forename: Nam-Hai
authors.initials: NH
authors.lastname: Chua
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics*; D001483:Base Sequence; D003001:Cloning, Molecular; D017931:DNA Primers; D018506:Gene Expression Regulation, Plant / Q000235:genetics; D005816:Genetic Complementation Test; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides; D010834:Phytochrome / Q000378:metabolism*; D051942:Phytochrome A; D015398:Signal Transduction / Q000502:physiology*; D014158:Transcription, Genetic / Q000235:genetics
chemical_list: D029681:Arabidopsis Proteins; D017931:DNA Primers; C483305:LAF3 protein, Arabidopsis; D009838:Oligodeoxyribonucleotides; C497973:PHYA protein, Arabidopsis; D051942:Phytochrome A; D010834:Phytochrome