Gracilaria tenuistipitata (Rhodophyta) tolerance to cadmium and copper exposure observed through gene expression and photosynthesis analyses

Abstract

Heavy metals are toxic to all organisms and their presence can have great impact on ecosystems. The study of strategies to remove contaminants is thus important, as is increased understanding of the resistance mechanisms of candidate organisms to be used as phytoremediators. The present study evaluate the genes involved in chronic stress using two different expression techniques to profile the transcriptome of the marine macroalga Gracilaria tenuistipitata after exposure to the EC50 of cadmium (Cd) and copper (Cu). Some known molecular markers for chronic pollution were observed, indicating that resistance mechanisms are induced within the first hour of treatment. Differences in gene expression response patterns between the two metals were found, where Cd up-regulated the expressions of superoxide dismutase and the nitrate transporter NRT even after 6 days of exposure. Expressions of both nuclear and chloroplast-encoded proteins were affected, and a stronger tolerance mechanism involving proteins of unknown function is certainly connected to the tolerance of the alga, warranting further studies. After 6 days of exposure to Cd or Cu, a slower acclimation was detected for the latter. Analysis of the photosynthetic rate revealed acclimation over time, corroborating a previous study where G. tenuistipitata was able to accumulate these metals and tolerate their negative effects, reinforcing the potential use of this macroalga in integrated bioremediation processes.