Bryophytes as metabolic engineering platforms

Metabolic engineering of plants offers significant advantages over many microbial systems such as cost-effective scalability and carbon autotrophy. Bryophytes have emerged as promising testbeds for plant metabolic engineering due to their rapid transformation and haploid-dominant lifecycle. The liverwort Marchantia polymorpha and the moss Physcomitrium patens are the best studied bryophytes and an expanding toolkit of genetic resources for both species allows for efficient pathway engineering. Bryophyte metabolism, while broadly conserved with seed plants, exhibits distinct features such as high diversity and amounts of terpenoids and very long-chain polyunsaturated fatty acids (vlcPFAs). In this review, we summarise the relatively limited understanding of bryophyte metabolism and how it diverges from seed plants. We argue that the success of bryophytes as testbed species will require new quantitative knowledge of fluxes in central metabolism and especially those that facilitate high rates of terpenoid and vlcPFA biosynthesis.