Genetic and genomic studies of seed -free plants: Sex determination in ferns and whole genome analysis of lycopods

The fern Ceratopteris richardii is a model system for studying sex determination in plants. While many sex determining mutants have been identified in Ceratopteris, cloning these genes has proven difficult. A new reverse genetics approach to identify the sex determination genes is described. This technique was successfully used to show that the Ceratopteris SCL6-like gene, shared between ferns and flowering plants, is required for male sex differentiation. We also provide evidence that this gene may be regulated by a microRNA in a sex specific manner. We have recently discovered that the lycopside Selaginella moellendorffii has the smallest genome of any vascular plant reported (∼100 Mb). To initiate whole genome studies of this emerging model plant genome, a sample whole genome shotgun (SWGS) sequence dataset as well as 270 kb of two BAC clones sequences surrounding the S. moellendorffii Scarecrow and Coumaroyl-3′-shikimate hydroxylase genes were obtained. This information was used to determine the proportion of coding, non-coding and repetitive DNA, and determine the likely number of genes in this small genome. The S. moellendorffii SWGS dataset was also compared to a simulated SWGS from Arabidopsis thaliana, another small genome plant species with a whole genome sequence already available. The results show that the ∼100 Mb of S. moellendorffii genome is likely to encode 18000 to 22000 genes