Abstract
Intertidal macroalgae are exposed to many abiotic stress factors, and they must regularly react to changes in their environment. We used RNA-seq to describe how Porphyra umbilicalis (Rhodophyta) changes gene expression patterns to interact with different habitats. Tissue samples were taken from a typical habitat along the open-coast of the Northwest Atlantic, as well as from a rare, atypical habitat in an estuarine tidal rapid environment. Differential gene expression analyses suggest that pathogic bacteria and viruses may be a significant factor influencing the transcriptome in the human-impacted estuarine environment, but the atypical habitat does not necessarily induce more stress in Porphyra umbilicalis growing there. We found genes related to nitrogen transport are over-expressed in tissue from the open-coastal site compared to those from the estuarine site, where environmental N levels approach hypertrophic levels. Low N levels impede growth, but high levels are toxic to cells, and we use qPCR to show this species regulates expression of a putative high-affinity NH4+ transporter under low and high N conditions. Differences in expression of this transporter in these habitats appear to be inherited from parent to offspring and have general implications for adaptation to habitat in other species that are capable of asexual reproduction, as well as more specific implications for this species’ use in aquaculture.
Highlights
Abiotic stress is a nearly universal factor affecting photosynthetic eukaryotes
More of the differentially expressed (DE) contigs were annotated by KEGG Automated Annotation Server (KAAS) (Table 3) and BLAST2GO (Table 4); contigs were assigned to nearly three times as many pathways
Compared to the FS g3 (FSg3) × FS g6 (FSg6) comparison, there was a greater abundance of DE putative Porphyra contigs associated with biosynthesis of secondary metabolites, plant-microbe-interaction pathways such as “infection by Vibrio cholerae,” and various plant antibiotic biosynthesis pathways (Table 5)
Summary
Abiotic stress is a nearly universal factor affecting photosynthetic eukaryotes. Some organisms deal with stressful environmental changes better than others, but few are capable of coping with variable environmental conditions better than intertidal algae. Porphyra umbilicalis Kützing is a species of marine red algae of the North Atlantic that is known for its tolerance of desiccation (Smith and Berry 1986), rapid osmotic changes (Reed et al 1980), and subzero temperatures (Wang et al 2011, Green and Neefus 2014) Some of this tolerance is due to cell structure and anatomy, but the physiological mechanisms by which they respond to abiotic stress are not well understood. Eriksen et al (2016) identified six Porphyra umbilicalis genotypes among populations in the Gulf of Maine based on a limited set of polymorphic microsatellite loci but showed isolation by distance is a more important factor influencing population structure than selection for habitat This suggests the populations acclimate to different stress conditions in different habitats through physiological adjustments
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