Closterium and Chara Genome and Transcriptome Analyses

Charophycean green algae are the closest living relatives to land plants.  To understand how plants evolved to live on land, we investigated two distantly related charophyceans, Closterium peracerosum-strigosum-littorale (p-s-l) complex and Chara braunii, which we can complete their lifecycle in laboratory. Closterium p-s-l complex is a species of desmids, unicellular algae.  We have sequenced its genome for the two mating types with HiSEQ2000.  Assembly from two libraries with insert size of 300 and 500 bp, we obtained about 330 Mb of scaffolds with N50 of 4.4 kb.  Investigating these data, we found that many of “plant-specific” genes including transcription factors are present in Closterium genome, most of which were not found in previously obtained 177,633 ESTs. Construction of mate-pair libraries and RNA-seq analyses are ongoing. Chara species have multicellular gametophyte (n) generation with complex differentiation of celltypes and organs. Rhizoid, protonema, thallus, antheridium, and oogonium (archegonium) are recognized.  For Chara braunii, we performed RNA-seq analysis from different tissues, which were assembled with ABySS.  Although we found some homologues of genes involved in plant development, some of gene families found in Closterium genome were not found in the transcriptome data. We are planning to read the genome sequence.