PHOTORESPONSES OF TRANSGENIC ARABIDOPSIS OVEREXPRESSING THE FERN ADIANTUM-CAPILLUS-VENERIS PHY1

The phytochrome gene (PHY1) cDNA from the fern Adiantum capillus-vener is encodes an amino acid sequence that shows equal similarity (50-60%) to all five Arabidopsis phytochromes (PHYA-E). The A. capillus-veneri s PHY1 cDNA was transformed into Arabidopsis ecotype Landsberg erecta to investigate its activity in angiosperms. Three of the resulting lin es contained at least 8 times more spectrally active phytochrome than the wild type, indicating that A. capillus-veneris phytochrome can inc orporate the chromophore of the host plants. Hypocotyl growth inhibiti on of these transgenic lines was investigated under red and far-red li ght. The results indicated dominant negative activity of A. capillus-v eneris phy1 on the phytochrome A response in the host plants under con tinuous far-red light. However, the fern phytochrome did not interfere with the red-light repression of hypocotyl growth mediated by endogen ous phytochrome B, and it failed to complement a phyB mutant phenotype . These observations suggest that the phy1 phytochrome molecule is too diverged from those of Arabidopsis to be fully functional.