Application of new genetic and analytic tools in the model moss Physcomitrium patens for membrane lipid research

• Applicant: Tegan Haslam, Ph.D.
• Subject Area: Plant Genetics and Genomics ; Plant Biochemistry and Biophysics ; Plant Cell and Developmental Biology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 539891731

Sphingolipids are among the most abundant components of plant plasma membranes, they are essential for membrane function and therefore plant viability. Specific sphingolipid headgroup modifications are required for normal growth and development, and sphingolipid content affects intercellular communication via plasmodesmata (PD). At present our mechanistic understanding of these roles is hindered by pleiotropic and non-viable phenotypes of most sphingolipid-deficient mutants in the classic genetic model, Arabidopsis thaliana. I propose investigating the mechanisms behind these roles of sphingolipids using the model moss Physcomitrium patens. P. patens is a complementary model to A. thaliana due to its simpler developmental patterning, the remarkable and rapidly expanding toolkit for its genomic manipulation, and its identity as a bryophyte, a phylogenetic clade sister to all vascular plants (tracheophytes). I will use a unique collection of sphingolipid-deficient mutants that I have developed in P. patens, optimized genomic manipulation tools, and cutting-edge targeted lipidomics to resolve the physiological impact of sphingolipid headgroup identity in P. patens. I will investigate sphingolipid roles in PD function using a cytosolic motility assay, and characterize PD structure and localized lipid content in the mutants showing the most severe motility defects. Polyunsaturated fatty acids (PUFAs) are major components of membrane lipids in bryophytes but not in tracheophytes. There has been rapid progress in characterizing the enzymes required for PUFA synthesis due to interest in metabolic engineering of this pathway in heterologous systems because of their status as essential fatty acids for human health. However, the physiological roles of PUFAs in bryophytes are unclear, as are the reasons for conservation of the PUFA synthetic pathway in bryophytes but not tracheophytes. I will investigate the impact of genetically modifying polyunsaturated fatty acid (PUFA) synthesis with a focus on downstream metabolic impacts and abiotic stress tolerance. This will produce valuable foundational knowledge and will support applied research enhancing PUFA production in crops for human use. Additionally, I will investigate and compare the condensing enzymes required for fatty acid elongation in A. thaliana and P. patens, using these models as a representative tracheophyte and bryophyte, respectively. Altogether, the proposed work will use state-of-the-art genomic manipulation tools and mass spectrometry techniques to address persistent, fundamental research questions related to membrane lipid synthesis and functions. It will also support applied work enhancing production of essential fatty acids for human health.

• DFG Programme: Research Grants