Burkhardt, I. | bioRxiv Science

bioRxiv2026

Convergent routes to haloterpenoid biosynthesis in red algae: identification of non-canonical UbiA-type terpene synthase gene clusters in the genus Laurencia

Red algae produce structurally diverse haloterpenoids unique to seaweeds, yet the enzymes responsible for generating many of their core terpene scaffolds remain unknown. Here, we report the identification of red algal UbiA-type terpene synthases (UTSs), a noncanonical enzyme family recently associated with terpene biosynthesis in bacteria and fungi. By prioritizing UbiA candidates located near putative biosynthetic genes, we identified eight candidate gene clusters across two red algal species, Laurencia pacifica and Laurencia subopposita. Using the heterologous host plant Nicotiana benthamiana, we show that the UbiA genes act as non-canonical TSs and that two UTSs produce the sesquiterpene bisabolene. The discovery of the bisabolene UTSs, LsUTS-2 and LpUTS-2, lays the foundation for laurane and chamigrane-type sesquiterpenoid production, addressing a prior biosynthetic quandary that bisabolene is not produced by established red algal class I TSs. Phylogenetic analyses distinguish the red algal UTSs from canonical UbiA prenyltransferases involved in primary metabolism and suggest they were acquired outside the red algal lineage. These findings expand the known distribution of UTSs and establish a previously unrecognized route to red algal terpene scaffolds.

biochemistry↗

bioRxiv2021

The termite fungal cultivar Termitomyces combines diverse enzymes and oxidative reactions for plant biomass conversion

Macrotermitine termites have domesticated fungi in the genus Termitomyces as their primary food source using pre-digested plant biomass. To access the full nutritional value of lignin-enriched plant biomass, the termite-fungus symbiosis requires the depolymerization of this complex phenolic polymer. While most previous work suggests that lignocellulose degradation is accomplished predominantly by the fungal cultivar, our current understanding of the underlying biomolecular mechanisms remains rudimentary. Here, we provide conclusive OMICs and activity-based evidence that Termitomyces partially depolymerizes lignocellulose through the combined actions of high-redox potential oxidizing enzymes (laccases, aryl-alcohol oxidases and a manganese peroxidase), the production of extracellular H2O2 and Fenton-based oxidative degradation, which is catalyzed by a newly described 2-methoxybenzoquinone/hydroquinone redox shuttle system and mediated by secreted chelating dicarboxylic acids. In combination, our approaches reveal a comprehensive depiction of how the efficient biomass degradation mechanism in this ancient insect agricultural symbiosis is accomplished through a combination of white- and brown-rot mechanisms. ImportanceFungus-growing termites have perfected the decomposition of recalcitrant plant biomass to access valuable nutrients by engaging in a tripartite symbiosis with complementary contributions from a fungal mutualist and a co-diversified gut microbiome. This complex symbiotic interplay makes them one of the most successful and important decomposers for carbon cycling in Old World ecosystems. To date, most research has focused on the enzymatic contributions of microbial partners to carbohydrate decomposition. Here we provide genomic, transcriptomic and enzymatic evidence that Termitomyces also employs redox mechanisms, including diverse ligninolytic enzymes and a Fenton-based hydroquinone-catalyzed lignin-degradation mechanism, to break down lignin-rich plant material. Insights into these efficient decomposition mechanisms open new sources of efficient ligninolytic agents applicable for energy generation from renewable sources.

microbiology↗