Abstract
BackgroundGinkgo biloba L. is the only surviving member of one of the oldest living seed plant groups with medicinal, spiritual and horticultural importance worldwide. As an evolutionary relic, it displays many characters found in the early, extinct seed plants and extant cycads. To establish a molecular base to understand the evolution of seeds and pollen, we created a cDNA library and EST dataset from the reproductive structures of male (microsporangiate), female (megasporangiate), and vegetative organs (leaves) of Ginkgo biloba.ResultsRNA from newly emerged male and female reproductive organs and immature leaves was used to create three distinct cDNA libraries from which 6,434 ESTs were generated. These 6,434 ESTs from Ginkgo biloba were clustered into 3,830 unigenes. A comparison of our Ginkgo unigene set against the fully annotated genomes of rice and Arabidopsis, and all available ESTs in Genbank revealed that 256 Ginkgo unigenes match only genes among the gymnosperms and non-seed plants – many with multiple matches to genes in non-angiosperm plants. Conversely, another group of unigenes in Gingko had highly significant homology to transcription factors in angiosperms involved in development, including MADS box genes as well as post-transcriptional regulators. Several of the conserved developmental genes found in Ginkgo had top BLAST homology to cycad genes. We also note here the presence of ESTs in G. biloba similar to genes that to date have only been found in gymnosperms and an additional 22 Ginkgo genes common only to genes from cycads.ConclusionOur analysis of an EST dataset from G. biloba revealed genes potentially unique to gymnosperms. Many of these genes showed homology to fully sequenced clones from our cycad EST dataset found in common only with gymnosperms. Other Ginkgo ESTs are similar to developmental regulators in higher plants. This work sets the stage for future studies on Ginkgo to better understand seed and pollen evolution, and to resolve the ambiguous phylogenetic relationship of G. biloba among the gymnosperms.
Highlights
Ginkgo biloba L. is the only surviving member of one of the oldest living seed plant groups with medicinal, spiritual and horticultural importance worldwide
It is widely believed that the survival of G. biloba depended upon Buddhist monks, who venerated the tree cultivated in their temple grounds, molecular evidence suggests that some stands in China (Wuchuan, Guizhou) are of natural origin representing vestige populations [6]
RNA was extracted from the following organs: megagasporangia, microsporangia and two sets of leaves collected from either male or female trees. mRNA isolated from all four tissues was used to construct four separate cDNA libraries. (Both male and female leaf sequences were pooled during subsequent bioinformatic analysis)
Summary
Ginkgo biloba L. is the only surviving member of one of the oldest living seed plant groups with medicinal, spiritual and horticultural importance worldwide. Ginkgo biloba is a widely popular tree that is native to China and has been cultivated for well over a millennium. Today's Ginkgo biloba is the sole surviving species of an ancient group (Ginkgophytes) of seed plants that may even date from the Permian (approximately 150–200 million years ago) [4]. It is widely believed that the survival of G. biloba depended upon Buddhist monks, who venerated the tree cultivated in their temple grounds, molecular evidence suggests that some stands in China (Wuchuan, Guizhou) are of natural origin representing vestige populations [6]. Ginkgo biloba has changed little in morphology from its extinct relatives [5]. Along with the Cycadales, Coniferales and Gnetales, the Ginkgoales is one of four orders of non-flowering seed plants (gymnosperms) that form a sister group to the angiosperms (Figure 1)
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