Zygnematophyceae - From living Algae collections to the establishment of future models

: The class of conjugating green algae, Zygnematophyceae (Conjugatophyceae), is extremely rich in species and has attracted interest of phycologists for a long time. It is now widely accepted that this class of Charophyte algae holds a key position in the phylogenetic tree of streptophytes where they represent the closest relatives to all land plants (embryophytes). In order to better understand the process of terrestrialization and the related molecular, cellular and physiological adaptations, the necessity of robust model plants allowing easy cultivation and genetic transformation becomes more and more evident. Living algae collections play an important role, not only for the phylogenomic-based taxonomy but also for the screening for suitable model organisms. For this review we screened six major public algae collections for Zygnematophyceae strains and established a cumulative list comprising 738 different taxa (including species, subspecies, varieties and forms). From the described biodiversity with 8883 registered taxa (Algaebase) the cultured Zygnematophyceae taxa worldwide cover only ca. 8.3%.. The past research on this clade of algae is reviewed and discussed under the perspective of model organism establishment. For the genera of Micrasterias and Spirogyra, representing the orders of Desmidiales and Zygnematales, we exemplarily present data on the life cycle. The current status of genetic transformation of Zygnematophyceae algae and future research perspectives are outlined.