The function of trehalose 6-phosphate in bryophytes and during the evolution of life on land

• Applicant: Dr. Franziska Fichtner
• Subject Area: Plant Physiology ; Evolution and Systematics of Plants and Fungi
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 527912383

Trehalose 6-phosphate (Tre6P) is a low abundance metabolite that plays an important role in flowering plants in regulating sugar metabolism, in developmental decision making, and in maintaining optimal sucrose levels. Tre6P is made by Tre6P synthase (TPS) and dephosphorylated by Tre6P phosphatase (TPP) into trehalose. Both, TPS and TPP proteins are present in all chloroplastida and have diversified in land plants, suggesting a key role of Tre6P during land plant evolution. Importantly, catalytically inactive TPS proteins are already found in streptophyte algae and bryophytes suggesting a function specifically for Tre6P signalling in these organisms. This is further supported by Tre6P-related genes responding transcriptionally in decapitated Physcomitrium patens shoots and Tre6P synthesis mutants in P. patens being unable to produce sporophytes. In Marchantia polymorpha TPS and TPP genes are highly expressed in reproductive structures suggesting a conserved role of Tre6P in reproduction in bryophytes. A TPP has been identified in interacting with a central regulator of the arbuscular mycorrhiza symbiosis program. However, a direct connection of Tre6P in mycorrhiza symbiosis is yet to be established. The presence of Tre6P synthesis and degradation genes in green algae and bryophytes, especially the occurrence of catalytically inactive forms, suggests that there is a function for Tre6P signalling which might have contributed to the evolution of land plants. The goal of this project is to uncover the role of Tre6P in sugar metabolism and developmental processes in both streptophyte algae and bryophytes by these three distinct objectives: 1) Investigating the role of Tre6P in regulating metabolism in streptophyte algae, 2) Identifying the function of Tre6P in regulating metabolism and development in bryophytes, and 3) Investigating the role of Tre6P in arbuscular mycorrhiza symbiosis in liverworts. The methods used will include growing different algae and bryophytes under varying light and carbon regimes to examine if Tre6P levels are responsive to changes in sugar availability and if changes in Tre6P levels result in a reprogramming of metabolism similar to what is observed in angiosperms. By genetic manipulation, Tre6P levels will be altered in bryophytes which will be combined with detailed metabolic and phenotypic analyses. This will help us to elucidate whether Tre6P is linked to nutrition in order to provide trehalose to plants as a storage and transport sugar, and/or regulates metabolic and developmental responses. Overall, the aim of this project is to determine if Tre6P is a signalling molecule that plays a crucial role in regulating metabolism and development in streptophytes and if it contributed to the adaptation of plants to life on land.

• DFG Programme: Priority Programmes
• Subproject of: SPP 2237: MAdLand — Molecular Adaptation to Land: plant evolution to change
• International Connection: Australia
• Cooperation Partner: Dr. Tom J. Fisher