The transcriptional modulation of desiccation tolerance factors in P. orbicularis explains its successful recuperation after water deficit. Differential responses to air exposure clarify seaweed distribution along intertidal rocky zones. Desiccation-tolerant seaweed species, such as Pyropia orbicularis, can tolerate near 96% water loss during air exposure. To understand the phenotypic plasticity of P. orbicularis to desiccation, several tolerance factors were assessed by RT-qPCR, Western-blot analysis, and enzymatic assays during the natural desiccation-rehydration cycle. Comparative enzymatic analyses were used to evidence differential responses between P. orbicularis and desiccation-sensitive species. The results showed that during desiccation, the relative mRNA levels of genes associated with basal metabolism [trehalose phosphate synthase (tps) and pyruvate dehydrogenase (pdh)] were overexpressed in P. orbicularis. Transcript levels related to antioxidant metabolism [peroxiredoxin (prx); thioredoxin (trx); catalase (cat); lipoxygenase (lox); ferredoxin (fnr); glutathione S-transferase (gst)], cellular detoxification [ABC transporter (abc) and ubiquitin (ubq)], and signal transduction [calmodulin (cam)] increased approximately 15- to 20-fold, with the majority returning to basal levels during the final hours of rehydration. In contrast, actin (act) and transcription factor 1 (tf1) transcripts were down-regulated. ABC transporter protein levels increased in P. orbicularis during desiccation, whereas PRX transcripts decreased. The antioxidant enzymes showed higher specific activity in P. orbicularis under desiccation, and sensitive species exhibited enzymatic inactivation and scarce ABC and PRX protein detection following prolonged desiccation. In conclusion, the reported findings contribute towards understanding the ecological distribution of intertidal seaweeds at the molecular and functional levels.

ABSTRACT. In rocky shores, desiccation is triggered by daily tide changes, and experimental evidence suggests that local distribution of algal species across the intertidal rocky zone is related to their capacity to tolerate desiccation. In this context, the permanence of Pyropia columbina in the high intertidal rocky zone is explained by its exceptional physiological tolerance to desiccation. This study explored the metabolic pathways involved in tolerance to desiccation in the Chilean P. columbina, by characterizing its transcriptome under contrasting conditions of hydration. We obtained 1,410 ESTs from two subtracted cDNA libraries in naturally hydrated and desiccated fronds. Results indicate that transcriptome from both libraries contain transcripts from diverse metabolic pathways related to tolerance. Among the transcripts differentially expressed, 15% appears involved in protein synthesis, processing and degradation, 14.4% are related to photosynthesis and chloroplast, 13.1% to respiration and mitochondrial function (NADH dehydrogenase and cytochrome c oxidase proteins), 10.6% to cell wall metabolism, and 7.5% are involved in antioxidant activity, chaperone and defense factors (catalase, thioredoxin, heat shock proteins, cytochrome P450). Both libraries highlight the presence of genes/proteins never described before in algae. This information provides the first molecular work regarding desiccation tolerance in P. columbina, and helps, to some extent, explaining the classical patterns of ecological distribution described for algae across the intertidal zone. Keywords: Pyropia, desiccation stress, ESTs, seaweeds, transcriptomics, proteins. Expresión diferencial de genes en Pyropia columbina (Bangiales, Rhodophyta)bajo hidratación y desecación natural RESUMEN. En zonas rocosas costeras, la desecación es gatillada por cambios diarios en los niveles de marea, y la evidencia experimental indica que la distribución de las algas en la zona intermareal está relacionada con su capacidad para tolerar la desecación. En este contexto, la presencia de Pyropia columbina en la zona alta del intermareal se explica por su excepcional tolerancia fisiológica a la desecación. Este estudio explora las vías metabólicas involucradas en la tolerancia a la desecación en P. columbina, a través de la caracterización de su transcriptoma bajo condiciones de hidratación contrastantes. Se obtuvo 1,410 ESTs provenientes de dos librerías de substracción de cDNA de frondas naturalmente hidratadas y desecadas. Los transcriptomas de ambas librerías contienen transcritos de diversas rutas metabólicas relacionadas a la tolerancia. Entre los transcritos expresados 15% están involucrados en la síntesis de proteínas, su procesamiento y degradación, 14,4% asociados a fotosíntesis y cloroplasto, 13,1% a respiración y función mitocondrial, 10,6% al metabolismo de la pared celular y 7,5% a la actividad antioxidante, proteínas chaperonas y factores de defensa (catalasa, tiorredoxina, proteínas de shock térmico, citocromo P450). En ambas librerías se de...

Abstract.-In primary producers, diverse stressors cause an over-production of methylglyoxal (MG), which is principally detoxified by glyoxalase I (GLO1) activity. A recent proteomic study found that GLO1 was up-regulated during natural desiccation in the red seaweed Pyropia orbicularis, which inhabits the upper intertidal rocky zone and compared to other species, is highly tolerant to air exposure. To better understand and determine differential responses to desiccation stress, this study evaluated MG concentration and GLO1 activity in two species with contrasted vertical distribution, P. orbicularis and Lessonia spicata (lower distribution). Results showed that P. orbicularis successfully scavenges MG via increased GLO1 activity during desiccation. In contrast, GLO1 activity in L. spicata did not increase during desiccation, resulting in MG overproduction. This study is the first to quantify MG and GLO1 levels in seaweeds during natural stress, and partly explain the mechanisms by which P. orbicularis is dominant in the upper rocky intertidal zone.

Variación espacio-temporal en la composición del ensamble de macroalgas del intermareal rocoso de Maitencillo, Valparaíso, costa central de Chile Spatio-temporal variation in the composition of the macroalgae assemblage of the intertidal rocky zone from Maitencillo, Valparaíso, central coast of Chile