1-Aminocyclopropane-1-carboxylic acid mitigates copper stress by decreasing copper transport and inducing jasmonic acid synthesis in Gracilariopsis lemaneiformis

Abstract

Severe marine pollution caused by excessive copper (Cu) has resulted in a great threat to marine biosystems. Gracilariopsis lemaneiformis, the main economically important cultivated macroalgal species of coastal China, is affected by Cu. 1-Aminocyclopropane-1-carboxylic acid (ACC), the direct precursor of ethylene, acts as a potential signaling molecule for plants to defend against heavy metal stress. In the present study, the role of ACC in alleviating Cu stress in G. lemaneiformis was explored by measuring physiological indicators and by performing a comparative transcriptome analysis. Excess Cu reduced photosynthetic rates and relative growth rates, increased Cu accumulation and malondialdehyde levels and induced the antioxidant system in G. lemaneiformis. ACC was found to inhibit the expression of genes encoding Cu transport proteins, greatly decrease Cu accumulation and MDA contents and relieve the inhibition of G. lemaneiformis growth caused by Cu stress. In addition, the expression of most antioxidant synthesis-related genes encoding SOD and APX was downregulated by ACC, and the activity of antioxidant enzymes was reduced. Moreover, ACC stimulated jasmonate acid (JA) synthesis to increase endogenous JA contents and activated pathways related to translation, photosynthesis, and nitrogen metabolism, while ACC did not stimulate the expression of genes involved in ethylene signaling pathways. These findings provide insight into the molecular mechanisms of Cu stress resistance in G. lemaneiformis and benefit the breeding and cultivation of G. lemaneiformis.