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- Increased evolutionary rates and conserved transcriptional response following allopolyploidization in brown algaePublication . Sousa, Filipe; Neiva, J.; Martins, Neusa; Jacinto, Rita; Anderson, Laura; Raimondi, Peter T.; Serrao, Ester; Pearson, GarethGenome mergers between independently evolving lineages, via allopolyploidy, can potentially lead to instantaneous sympatric speciation. However, little is known about the consequences of allopolyploidy and the resultant "genome shock" on genome evolution and expression beyond the plant and fungal branches of the Tree of Life. The aim of this study was to compare substitution rates and gene expression patterns in two allopolyploid brown algae (Phaeophyceae and Heterokonta) and their progenitors in the genus Pelvetiopsis N. L. Gardner in the north-east Pacific, and to date their relationships. We used RNA-seq data, all potential orthologues, and putative single-copy loci for phylogenomic, divergence, and gene expression analyses. The multispecies coalescent placed the origin of allopolyploids in the late Pleistocene (0.35-0.05 Ma). Homoeologues displayed increased nonsynonymous divergence compared with parental orthologues, consistent with relaxed selective constraint following allopolyploidization, including for genes with no evidence of pseudogenization or neofunctionalization. Patterns of homoeologue-orthologue expression conservation and expression level dominance were largely shared with both natural plant and fungal allopolyploids. Our results provide further support for common cross-Kingdom patterns of allopolyploid genome evolution and transcriptional responses, here in the evolutionarily distinct marine heterokont brown algae.
- Congruence between fine-scale genetic breaks and dispersal potential in an estuarine seaweed across multiple transition zonesPublication . Nicastro, Katy; Assis, J.; Serrao, Ester; Pearson, Gareth; Neiva, J.; Valero, Myriam; Jacinto, Rita; Zardi, Gerardo, IGenetic structure in biogeographical transition zones can be shaped by several factors including limited dispersal across barriers, admixture following secondary contact, differential selection, and mating incompatibility. A striking example is found in Northwest France and Northwest Spain, where the estuarine seaweed Fucus ceranoides L. exhibits sharp, regional genetic clustering. This pattern has been related to historical population fragmentation and divergence into distinct glacial refugia, followed by post-glacial expansion and secondary contact. The contemporary persistence of sharp ancient genetic breaks between nearby estuaries has been attributed to prior colonization effects (density barriers) but the effect of oceanographic barriers has not been tested. Here, through a combination of mesoscale sampling (15 consecutive populations) and population genetic data (mtIGS) in NW France, we define regional genetic disjunctions similar to those described in NW Iberia. Most importantly, using high resolution dispersal simulations for Brittany and Iberian populations, we provide evidence for a central role of contemporary hydrodynamics in maintaining genetic breaks across these two major biogeographic transition zones. Our findings further show the importance of a comprehensive understanding of oceanographic regimes in hydrodynamically complex coastal regions to explain the maintenance of sharp genetic breaks along continuously populated coastlines.
- Carotenoid biosynthetic gene expression, pigment and n-3 fatty acid contents in carotenoid-rich Tetraselmis striata CTP4 strains under heat stress combined with high lightPublication . Schüler, Lisa Maylin; Bombo, Gabriel; Duarte, Paulo; Santos, Tamara; Maia, Inês Beatriz; Pinheiro, Filipa; Marques, José; Jacinto, Rita; Schulze, Peter S.C.; Pereira, Hugo; Barreira, Luísa; Varela, JoãoIn this study, two carotenoid-rich strains of the euryhaline microalga Tetraselmis striata CTP4 were isolated by random mutagenesis combined with selection via fluorescence activated cell sorting and growth on norflurazon. Both strains, ED5 and B11, showed an up to 1.5-fold increase in carotenoid contents as compared with the wildtype, independent of the growth conditions. More specifically, violaxanthin, beta-carotene and lutein contents reached as high as 1.63, 4.20 and 3.81 mg g-1 DW, respectively. Genes coding for phytoene synthase, phytoene desaturase, lycopene-beta-cyclase and epsilon-ring hydroxylase involved in carotenoid biosynthesis were found to be upregulated in ED5 and B11 cells as compared to the wildtype. Both strains showed higher contents of eicosapentaenoic acid as compared with those of the wildtype, reaching up to 4.41 and 2.88 mg g-1 DW, respectively. Overall, these results highlight the complexity of changes in carotenoid biosynthesis regulation that are required to improve pigment contents in microalgae.
- Enhancement of heat tolerance by salt stress in Tetraselmis striata CTP4: impacts on HSP gene expression, pigments, and proximal compositionPublication . Santos, Tamara; Pereira, Hugo; Maia, Inês Beatriz; Jacinto, Rita; Bombo, Gabriel; Ribeiro Pinheiro, Filipa Maria; Barreira, Luísa; Varela, JoãoAs the world average temperature is on the rise and heat waves are becoming more prevalent, microalgal producers have been facing significant challenges regarding the time periods during which they are able to grow less thermotolerant microalgae in outdoor production facilities. Therefore, it is urgent to explore how microalgae cope with thermal stress and under which growth conditions tolerance to temperatures close to or higher than their maximum thermal threshold is induced. For this purpose, Tetraselmis striata CTP4, a euryhaline microalga known for its thermotolerance, was selected. Tetraselmis striata belongs to the Chlorodendrophyceae, a clade that branched off early from other "core chlorophyte" clades, usually comprised of microalgae able to colonise freshwater habitats. Here, we present compelling evidence that the ability of this microalga to withstand otherwise lethal thermal upshifts to 40 degrees C is induced by exposure to higher salinity (35 ppt). In contrast, this response is abrogated at lower salinities. Concomitantly, the expression of genes encoding HSP70 and HSP100, two heat shock proteins known to mediate thermotolerance and tolerance to other stresses (e.g., salt stress) in fungi, animals and plants, was enhanced when exposed to both heat stress and higher salinities. This suggests that cross-protective mechanisms against abiotic stress appeared early during the evolution of the core chlorophytes and of Archaeplastida in general. This knowledge can be used to select novel strains and growth conditions that promote thermotolerance in microalgae that are grown in outdoor industrial production facilities in environments where heat waves are expected.