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

Three cDNAs for phytochrome A (phyA), designated ArPHYA1, ArPHYA2 and ArPHYA3, 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 stronger homology to the product of PHYA of Arabidopsis thaliana than to products of genes for phytochromes of many other plant species. Levels of transcripts 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 proximal parts decreased by 25-50% after light irradiation. The elevated levels of transcripts of PHYA genes at the proximal ends of hairy roots are discussed with reference to the light-induced formation of adventitious shoots.