Ginkgo biloba Retains Functions of Both Type I and Type II Flowering Plant Phytochrome

While the photoreceptor systems of flowering plants have been well studied, the origins of these gene families and their functions are only partially understood. To begin to resolve the evolutionary origins of angiosperm photoreceptor function, we have studied the photomorphogenic responses of the early diverging gymnosperm Ginkgo biloba. Here, we describe the effects of continuous white light, red light, far-red light, and blue light on stem length, chlorophyll accumulation, Lhcb mRNA accumulation, and plastid development. Differences in the efficacy of these light regimes on de-etiolation in Ginkgo suggest separate but complementary roles for red and blue light-sensing systems. Additionally, the unique manner in which developmental regulation occurs in Ginkgo reveals a far-red high irradiance response different from both angiosperm and other gymnosperm species. We conclude from these data that Ginkgo contains a functional complement to both flowering plant type I and type II phytochromes, as well as independent blue light-sensing system(s). The implications of these findings are discussed with respect to the evolution of higher plant photoreceptors.