Response of key stress-related genes of the seagrass <i>Posidonia oceanica</i> in the vicinity of submarine volcanic vents

Abstract

Abstract. Submarine volcanic vents are being used as natural laboratories to assess the effects of increased ocean acidity and carbon dioxide (CO 2 ) concentration on marine organisms and communities. However, in the vicinity of volcanic vents other factors in addition to CO 2 , which is the main gaseous component of the emissions, may directly or indirectly confound the biota responses to high CO 2 . Here we used for the first time the expression of antioxidant and stress-related genes of the seagrass Posidonia oceanica to assess the stress levels of the species. Our hypothesis is that unknown factors are causing metabolic stress that may confound the putative effects attributed to CO 2 enrichment only. We analyzed the expression of 35 antioxidant and stressrelated genes of P. oceanica in the vicinity of submerged volcanic vents located in the islands of Ischia and Panarea, Italy, and compared them with those from control sites away from the influence of vents. Reverse-transcription quantitative polymerase chain reaction (RT-qPCR) was used to characterize gene expression patterns.Fifty-one percent of genes analyzed showed significant expression changes. Metal detoxification genes were mostly down-regulated in relation to controls at both Ischia and Panarea, indicating that P. oceanica does not increase the synthesis of heavy metal detoxification proteins in response to the environmental conditions present at the two vents. The up-regulation of genes involved in the free radical detoxification response (e.g., CAPX, SODCP and GR) indicates that, in contrast with Ischia, P. oceanica at the Panarea site faces stressors that result in the production of reactive oxygen species, triggering antioxidant responses. In addition, heat shock proteins were also activated at Panarea and not at Ischia. These proteins are activated to adjust stressaccumulated misfolded proteins and prevent their aggregation as a response to some stressors, not necessarily high temperature. This is the first study analyzing the expression of target genes in marine plants living near natural CO 2 vents. Our results call for contention to the general claim of seagrasses as "winners" in a high-CO 2 world, based on observations near volcanic vents. Careful consideration of factors that are at play in natural vents sites other than CO 2 and acidification is required. This study also constitutes a first step for using stress-related genes as indicators of environmental pressures in a changing ocean.

Nutrient Loading Fosters Seagrass Productivity Under Ocean Acidification

“…Expression level analyses were performed for specific genes of interest (GOIs) (See Table 3 and Supplementary Table S1 list selected genes of interest, their functions and primer information): the glutathione related enzymes glutathione synthase (GSH-S), glutathione peroxidase (GPX), glutathione reductase (GR) and glutathione S-transferase (GST), the antioxidant enzymes catalase (CAT), superoxide dismutase (SOD), luminal binding protein (LBP) and Peroxiredoxin Q (PRXQ) 27 , 70 and three nitrate transportes (NRT1_6.3, NRT1_2.13 and NRT2). Glutathione-related and the other antioxidant enzymes were selected in order to study the cellular response to oxidative stress, while nitrate transporters were selected to investigate variations in nitrogen uptake upon nutrient-enrichment.…”

“…Recently, Lauritano, et al . 27 compared the expression of genes involved in the response to stress between plants collected at low natural pH, near volcanic vents, and plants collected at normal pH conditions. These authors found increased expression of some antioxidant and stress-related genes in epiphyte-free leaves of P. oceanica close to vents, suggesting overall negative effects of increased CO 2 and low pH on plant physiology, possibly triggered by extensive leaf epiphyte loss 22 .…”

“…In particular, previous studies carried out at Ischia Island vents have extensively demonstrated that areas exposed to CO 2 bubbling do not differ from control areas in terms of temperature, hydrodynamic conditions, salinity, light and total alkalinity, by virtue of the fact that they are just 10 s of m apart 14 , 30 , 32 , 33 . As a consequence of temporal fluctuations in pH and the presence of other components deriving from the volcanic activity, vents are not perfect predictors of OA effects on marine systems 14 , 27 , 34 . On the other hand, they allow the integration of species interactions and seasonal cycles, unlikely to be achieved under laboratory settings.…”

Proteome Analysis Reveals Extensive Light Stress-Response Reprogramming in the Seagrass Zostera muelleri (Alismatales, Zosteraceae) Metabolism

“…Altogether, the differential regulation of proteins involved in the AsA-GsH cycle and flavonoid pathway indicates that SSL conditions triggered the plant antioxidant defense system, which improved the redox status and thus the SSL tolerance of Z. muelleri . Differential regulation of these antioxidant enzymes has been well documented as a defense response of seagrasses to light stress, heavy metal toxicity, and ocean acidification (Li et al, 2012; Dattolo et al, 2013; Lauritano et al, 2015). However, down-regulation of superoxide dismutase (SOD-Cu/Zn) and germin-like protein (that has both SOD and oxalate oxidase activity) suggests that this species is sensitive to high light stress.…”

Molecular physiology reveals ammonium uptake and related gene expression in the seagrass Zostera muelleri

“…These molecular events precede population-level changes and could be useful biomarkers if they can be linked to specific physiological or ecological events (Macreadie et al, 2014b). Thus, seagrass researchers have recently taken advantage of the power of genomics and transcriptomics to address questions about the molecular mechanisms of ecological responses to environmental perturbations (Franssen et al, 2011, Franssen et al, 2014, Dattolo et al, 2014, Serra et al, 2012, Lauritano et al, 2015, Salo et al, 2015, Brakel et al, 2014. Following the recent publication of Zostera marina genome (Olsen et al, 2016), the seagrass community is now eagerly awaiting the progress that will be promoted by integrating molecular biology and gene expression into the spectrum of physiological and metabolic changes involved in the response of seagrass to environmental stress.…”