Wolffia australiana Genome sequencing and assembly

Wolffia (watermeal; water eggs; Khai Nam) is part of a family of aquatic non-grass monocots known as Duckweeds (Lemnaceae). Wolffia has the distinction of being the Duckweed genus with the smallest (Wolffia angusta) as well as the fastest growing (Wolffia microscopica) species of known flowering plants. Plants belonging to this genus are highly reduced in their morphology and anatomy, lacking roots and containing only the green floating frond, which is essentially a fused leaf and stem without any vasculature. Wolffia typically measure only a few millimeters to less than a millimeter in size and grow as colonies of two individuals, one mother frond budding and giving rise to one or very rarely two daughter fronds within a colony. Anatomically, however, at least four different generations of plants (total of 10-14 individuals) can be found within the plant, highlighting their adaptive preparedness for fast vegetative multiplication. There are five genera of duckweed (Spirodela, Landoltia, Lemna, Wolffiella and Wolffia), and their genome sizes span an order of magnitude. The Greater Duckweed, Spirodela polyrhiza, which is most basal with the largest body size, has the smallest genome at 158 megabase (Mb), while Wolffia, the most derived genus of the Duckweed family, has genomes that span from W. australiana at 357 Mb to W. arrhiza at 1,881 Mb. We generated sequence for two accession of the smallest Wolffia, W. australiana, using Pacific Biosystems (PacBio) RSII Single Molecule Real-time (SMRT) sequencing. High quality assemblies were generated with Canu and the genomes were annotated using deep time-of-day (TOD) Illumina RNAseq expression data.