The characterisation of Arabidopsis plants expressing lower plant phytochromes

Two phytochrome-like gene fragments have been isolated using a degenerate PCR strategy from the fern Pteridium aquilinum (bracken). Both share a high degree of similarity with each other and to previously isolated phytochromes. In an attempt to isolate larger phytochrome gene fragments and full length phytochrome genes a cDNA library was constructed from light-grown young bracken fronds. The library was screened with one of the bracken phytochrome fragments. The low level of abundance of phytochrome message, however, hindered the isolation of phytochrome genes from the cDNA library.;The high degree of sequence homology between lower and high plant phytochromes has led to speculation on whether or not lower plant phytochromes can be functional in higher plants. This speculation can be addressed by expressing the lower plant phytochromes transgenically in higher plants and assaying for biological function.;Arabidopsis thaliana ecotype Landsberg erecta has been transformed using an Agrobacterium mediated root explant transformation system with a phytochrome-like gene isolated from the fern Anemia phyllitidis. The phytochrome gene, PHY3 was placed under the control of a double 35S cauliflower mosaic virus (CaMV) promoter. A second construct has also been used to transform Arabidopsis containing the NH2-terminal half of Anemia PHY3 gene fused to the C-terminal half of oat PHYA. This construct was also attached to a CaMV promoter. Expression of these two constructs causes a reduction in sensitivity of the seedlings to continuous FR. This decreased sensitivity results in a long hypocotyl phenotype under FR, a reduction in anthocyanin production in FR and an inability of FR to block greening. The transgenic lines, however, showed a WT response to VLF light. It is apparent that the expression of the Anemia PHY3 gene is, in some way, interfering with the normal transduction of the phyA signalling pathway. The interference is restricted to the FR HIR.