Comparative transcriptome analysis reveals chitooligosaccharides-induced stress tolerance of Gracilariopsis lemaneiformis under high temperature stress

Gracilariopsis lemaneiformis, one of the principal economical seaweeds in China, has been increasingly threatened by diseases and yield reduction due to heat stress caused by global warming. Reportedly, chitooligosaccharides (COS) can be used as an elicitor to induce the defense response of terrestrial plants. This study aimed to investigate the possibility of using COS as an elicitor to induce the stress resistance of G. lemaneiformis under heat stress. The present results showed that COS can relieve the adverse effects of high temperatures on G. lemaneiformis. After treatment with different concentrations of COS, the relative growth rate (RGR) of G. lemaneiformis was remarkably improved, while its level of lipid peroxidation was significantly decreased under heat stress. To illustrate the response mechanism of G. lemaneiformis to COS, a comparative transcriptome analysis was performed, which revealed COS-responsive differentially expressed genes and metabolic pathways after 24 and 48 h of heat stress treatment. COS elicitation was able to activate signal transduction, particularly in mitogen-activated protein kinase (MAPK) cascades and phosphatidylinositol signaling system, which might further regulate the photosynthesis, energy metabolism and antioxidant systems in G. lemaneiformis. Meanwhile, alpha-linolenic acid metabolism, associated with the synthesis of jasmonates, was also responsive to COS, indicating that jasmonates may be involved in COS-mediated defense responses in G. lemaneiformis. Furthermore, the transcriptome results were in general consistent with the changes in physiological parameters associated with photosynthesis and antioxidant systems. These findings can facilitate our understanding of the molecular mechanisms on the heat tolerance of G. lemaneiformis and provide a new viewpoint for the future breeding of thermotolerant G. lemaneiformis.