Rapid advances in DNA synthesis techniques have allowed the assembly and engineering of viral and microbial genomes. Multicellular eukaryotic organisms, with their larger genomes, abundant transposons, and prevalent epigenetic regulation, present a new frontier to synthetic genomics. Plant synthetic genomics have long been proposed, and exciting progress has been made using the top-down approach. In this perspective, we propose applying bottom-up genome synthesis in multicellular plants, starting from the model moss Physcomitrium patens , in which homologous recombination, DNA delivery, and regeneration are possible, although further optimizations are necessary. We then discuss technical barriers, including genome assembly and plant transformation, associated with synthetic genomics in seed plants.