Pumping Iron: A Multi-omics Analysis of Two Extremophilic Algae Reveals Iron Economy Management

Marine algae are responsible for half of the worlds primary productivity, but this critical carbon sink is often constrained by insufficient iron. One species of marine algae, Dunaliella tertiolecta, is remarkable for its ability to maintain photosynthesis and thrive in low-iron environments. A related species, Dunaliella salina Bardawil, shares this attribute but is an extremophile found in hyper-saline environments. To elucidate how algae manage their iron requirements, we produced high-quality genome assemblies and transcriptomes for both species to serve as a foundation for a comparative multi-omics analysis. We identified a host of iron-uptake proteins in both species, including a massive expansion of transferrins and a novel family of siderophore-iron uptake proteins. Complementing these multiple iron-uptake routes, ferredoxin functions as a large iron reservoir that can be released by induction of flavodoxin. Proteomic analysis revealed reduced investment in the photosynthetic apparatus coupled with remodeling of antenna proteins by dramatic iron-deficiency induction of TIDI1, an LHCA-related protein found also in other chlorophytes. These combinatorial iron scavenging and sparing strategies make Dunaliella unique among photosynthetic organisms. Significance StatementDespite their small size, microalgae play a huge role in CO2 uptake via photosynthesis, and represent an important target for climate crisis mitigation efforts. Most photosynthesis proteins require iron as a co-factor so that insufficient iron often limits algal CO2 sequestration. With this in mind, we examined a genus of microalgae called Dunaliella that is exceptionally well-adapted to low iron environments. We produced complete genomes, transcriptomes, and proteomes for two species of Dunaliella that hail from radically different environments: one from coastal ocean waters and the other from salt flats. We identified dozens of genes and multiple, complementary strategies that both species utilize for iron-uptake and management that explain Dunaliellas remarkable ability to thrive on low iron.