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

Abstract. Submarine volcanic vents are being used as natural laboratories to assess the effects of increased ocean acidity and carbon dioxide (CO₂) concentration on marine organisms and communities. However, in the vicinity of volcanic vents other factors in addition to CO₂, which is the main gaseous component of the emissions, may directly or indirectly confound the biota responses to high CO₂. 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 CO₂ enrichment only. We analyzed the expression of 35 antioxidant and stress-related 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 stress-accumulated 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 CO₂ vents. Our results call for contention to the general claim of seagrasses as "winners" in a high-CO₂ world, based on observations near volcanic vents. Careful consideration of factors that are at play in natural vents sites other than CO₂ 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.