Mesostigma viride isolate:NIES-296 Genome sequencing and assembly. Mesostigma viride isolate:NIES-296

Multicellular land plants evolved from charophyte green algae. Lacking of the genome sequence of unicellular charophyte green algae hindered the understanding of the transition from unicellular to multicellular life-style in Streptophyta. Here, we report a high quality reference genome of Mesostigma viride, a single celled charophyte alga with its unique phylogenetic position at the base of Streptophyta. There are abundant segmental duplications and transposable elements in M. viride contributing to a relatively large genome with a high gene content in comparison to other algae and early land plants. We identify the origin of genetic tools that land plants inherited, including those associated with epigenetics, transcriptional or post-transcriptional regulation of gene expression, and photosynthesis. The paucity of homologs related to phytohormones and the lack of those associated with plant-like stress responses in our transcriptome dataset implicate their presence after the divergence of M. viride. Our genomic resources are thus vital towards addressing the age-old question of the evolution of multicellularity and ultimately the land plants.