Phytochromes are the photoreceptors mainly responsible for the detection of red and far-red (FR) light and the following responses. HFR1 is a basic helix-loop-helix type putative transcription factor involved in Phytochrome A signaling pathway. First we look at the early phenotype of mutant seedlings lacking a functional HFR1 gene and we show that auxin is involved in the increased hypocotyl phenotype of these seedlings. Northern blots and RT-PCRs showed that ATHB-2, a gene involved in shade avoidance is regulated by HFR1 under FR light. Microarray experiments were performed to find the genes that are early targets of regulation by HFR1.