Abstract
Gracilariopsis lemaneiformis (G. lemaneiformis) is an important marine red macroalgae with high economic and ecological value all over the world. To date, global warming is a key issue that has a great impact on all living organisms, such as macroalgae. L-arginine (Arg) is a precursor of nitric oxide (NO) and polyamines (PAs), which can induce stress defense responses in land plants. However, its role in inducing algae resistance at high temperature (HT) is unclear. In this study, G. lemaneiformis thalli were treated with different concentrations of Arg to investigate its effect and the mechanism on the tolerance of G. lemaneiformis against HT stress. It turned out that exogenous Arg significantly alleviated the HT-induced oxidative damage as indicated by a markedly decrease in malondialdehyde (MDA) content. Notably, Arg remarkably improved the relative growth rate (RGR) and phycobiliprotein (PBP) contents of G. lemaneiformis at HT. Moreover, Arg significantly elevated the activities of antioxidant enzymes, such as superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), to efficiently scavenge reactive oxygen species (ROS). In addition, it also promoted the accumulation of free amino acids (AAs) as compared to those in the control treatment (CK) group under HT conditions. To investigate the mechanism of G. lemaneiformis to Arg, a transcriptome analysis was performed and revealed 1,414 and 3,825 differentially expressed genes (DEGs) in Arg-treated groups as compared to CK groups at 24 and 48 h of HT stress, respectively. Results showed that Arg significantly upregulated the expression of genes encoding antioxidant enzymes, heat shock proteins, and triggered transcription factors (TFs) signaling during HT stress. Moreover, Arg enhanced the DEGs involved in arginine and proline (Pro) metabolism, AAs biosynthesis, glycolysis, tricarboxylic acid (TCA) cycle, and oxidative phosphorylation. These results may help in understanding the role of Arg in G. lemaneiformis resistance to HT and provide a practical viewpoint for obtaining heat-tolerant G. lemaneiformis to further promote the development of the cultivated seaweed industry in the future.
Highlights
Gracilariopsis lemaneiformis (G. lemaneiformis; Rhodophyta) is one of the most cultivated seaweeds around the world, especially in China and Indonesia (Kim et al, 2017), ranking second in Chinese cultivated macroalgae production with an annual yield exceeding 300,000 tons based on data in 2019 (China Fishery Statistics Yearbook, 2020)
Both 0.5 and 1 mM Arg treatments were efficient in alleviating high temperature (HT) stress-triggered decrease of algal PBP, but there was no significant difference between the two concentrations (Supplementary Figures 1B,C)
Expressed Genes Encoding Heat Shock Proteins In the present study, we found that genes involved in Heat Shock Proteins (HSPs) were markedly activated in G. lemaneiformis with Arg treatment under HT stress
Summary
Gracilariopsis lemaneiformis (G. lemaneiformis; Rhodophyta) is one of the most cultivated seaweeds around the world, especially in China and Indonesia (Kim et al, 2017), ranking second in Chinese cultivated macroalgae production with an annual yield exceeding 300,000 tons based on data in 2019 (China Fishery Statistics Yearbook, 2020). Gracilariopsis lemaneiformis is a valuable resource with high protein and low lipid and rich in polysaccharides, dietary fiber, minerals, essential amino acids (AAs), and trace elements (Han et al, 2012). It is widely used in the agar industry, and be applied to mitigate red tide and eutrophication for marine ecological restoration (Zhou et al, 2006; Sun et al, 2018). With the rising global and local temperatures, the G. lemaneiformis cultivation in the southern coast of China has been seriously affected
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