Photomorphogenesis in the gymnosperm Ginkgo biloba and the divergence of type-specific phytochrome function

Despite advances in the understanding of flowering plant phytochrome gene function, and the accumulation of diverse plant phytochrome sequences, a structure/function relationship has yet to be established linking type-specific phytochrome responses to their molecular determinants. Hence, the relationship between lower plant and angiosperm phytochrome has been unclear. In this study, I set out prove whether type-specific phytochrome functions arose prior to divergence of their sequences and from this information hoped to gain insight regarding the regulation of phytochrome function in time and 3-dimensional space. By monitoring the responses of Ginkgo to various light conditions, I have been able to compare the capacity for light perception in this organism to that of model flowering plants. In short, while Ginkgo is capable of mediating both flowering plant Type I and Type II phytochrome responses (functions of phyA and phyB, respectively), it is less sensitive to light than flowering plants. I have also found that Bc is most effective at stimulating photomorphogenic events in seedling stems and that these events are apparently regulated in a novel manner.; While the deduced amino acid sequence of the only Ginkgo phytochrome molecule identified in this study (GbPHY1), appears to be slightly more related to Arabidopsis PHYB than PHYA, there is reason to believe that GbPHY 1 is involved in mediating both phyA and phyB-related responses. Direct sequence comparisons revealed a small region that shows higher homology to PHYA than PHYB, and whose predicted structure and phylogeny suggest that this region may be involved in determining phytochrome type-specificity. Since functional information regarding gymnosperm phytochrome is largely unavailable, type-specificity for these phytochrome sequences has only been speculative. If the small region identified in this study indeed has functional significance, this would suggest that comparisons based solely on sequence could be misleading.