Multiple transcription-factor genes are early targets of phytochrome A signaling

The phytochrome family of sensory photoreceptors directs adaptational chang es in gene expression in response to environmental light signals. Using oli gonucleotide microarrays to measure expression profiles in wild-type and ph ytochrome A (phyA) null-mutant Arabidopsis seedlings, we have shown that 10 % of the genes represented on the array are regulated by phyA in response t o a continuous far-red light signal. Strikingly, 44% of the genes respondin g to the signal within 1 h are predicted to encode multiple classes of tran scriptional regulators. Together with previous data, this observation sugge sts that phyA may regulate seedling photomorphogenesis by direct targeting of light signals to the promoters of genes encoding a master set of diverse transcriptional regulators, responsible in turn for orchestrating the expr ession of multiple downstream target genes in various branches of a phyA-re gulated transcriptional network.