Genes for phytochrome A in horseradish: isolation of cDNAs and analysis ofexpression during light-induced formation of adventitious shoots from hairy roots

Three cDNAs for phytochrome A (phyA), designated ArPHYA1, ArPHYA2 and ArPHY A3, respectively, were isolated from a cDNA library prepared from proximal parts of the hairy roots of horseradish (Armoracia rusticana). The level of phyA was higher in those parts than in any other parts of hairy roots. The amino acid sequences deduced from the cDNAs were quite similar, with stron ger homology to the product of PHYA of Arabidopsis thaliana than to product s of genes for phytochromes of many other plant species. Levels of transcri pts in roots and tubers were higher than those in leaves and petioles. The levels in hairy roots were highest at the proximal ends and increased with increased duration of culture in darkness. Furthermore, the levels in proxi mal parts decreased by 25-50% after light irradiation. The elevated levels of transcripts of PHYA genes at the proximal ends of hairy roots are discus sed with reference to the light-induced formation of adventitious shoots.