The amphibious liverwort Riccia fluitans:A novel model organism to analyze adaptive land plant features

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TCP transcription factors (TFs) are known to exert crucial regulatory functions in angiosperm development. Recently, we detected that the Marchantia polymorpha TF MpTCP1 exhibits a growth regulatory function and also governs the formation of novel plant pigments, which might mediate protective functions against abiotic stress. Plant terrestrialization likely started from a freshwater environment, where ancestors of land plants experienced water scarcity. The first land plants were thus facing novel abiotic stressors such as drought and high light intensities. To investigate adaptive molecular mechanisms enabling the conquest of land, the emerging model organism Riccia fluitans is ideally suited, as this amphibious liverwort can strive in aquatic as well as terrestrial habitats. Given its striking developmental plasticity, this liverwort can adapt thallus development to different habitats. Desiccation of the R. fluitans water form causes the formation of typical land plant structures: rhizoids as anchoring structures, air pores for gas exchange and a repellent surface. We will advance the tool box for R. fluitans and analyze the RfTCP1 activities by generating and investigating CRISPR/Cas9-induced mutants. The R. fluitans water and land forms also differ in their meristematic activities, thereby mediating thallus growth differences. The redox-sensitive MpTCP1 protein activity controls a complex downstream redox network, affecting also growth. We aim to investigate the impact of redox processes on meristematic activities and the formation of adaptive land plant features and in changing, challenging environments.