Sexual reproduction in Zygnematophyceae (Charophyta)

This project will investigate Zygnematophyceae, the closest relatives to land plants. The reason for their evolutionary success is still unknown. Data on vegetative survival strategies of these algae are already available. While young freshly divided cells are less stress tolerant, they gain tolerance through a maturation process which leads to the formation of akinetes. These akinetes contain lipids and other storage products, which enable them to overwinter. Also, a protection against abiotic stress like desiccation and ultraviolet radiation is given. However, information on their sexual reproduction is scarce. During conjugation two mating algal filaments arrange closely, form copulation channels and fuse to diploid zygotes. These zygotes also undergo a maturation process which leads to permanent stages termed zygospores. During this process cell wall material is formed and a three-layered zygospore wall is built up, which is particularly resistant against environmental impact. Therefor zygospores have the capacity to tolerate unfavorable conditions for a longer period as akinetes. One key is the formation of a special waterproof layer in the zygospore wall, termed mesospor which contains polymeric substances comparable to the composition of higher plant pollen grains. The investigation of these substances with different methods is a central aim of this project. The project shall produce information on the whole sexual reproduction (conjugation, zygospore maturation and germination) of Zygnematopyhceae and investigate if these strategies are correlated to their success on land. The Austrian research team will investigate these questions by phylogenetic, physiological, ultrastructural, molecular and biochemical methods in joint effort with international cooperation partners from Germany and the US. The results will give new insights in understanding of plant terrestrialization.