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. 2023 Oct 2;24(19):14825.
doi: 10.3390/ijms241914825.

Alleviative Effect of Iodine Pretreatment on the Stress of Saccharina japonica (Phaeophyceae, Laminariales) Caused by Cadmium and Its Molecular Basis Revealed by Comparative Transcriptomic Analysis

Xuemei Wang  1 , Tifeng Shan  1   2 , Shaojun Pang  1   2
Affiliations

Alleviative Effect of Iodine Pretreatment on the Stress of Saccharina japonica (Phaeophyceae, Laminariales) Caused by Cadmium and Its Molecular Basis Revealed by Comparative Transcriptomic Analysis

Xuemei Wang et al. Int J Mol Sci. .

Abstract

Iodide is accumulated by the brown alga Saccharina japonica at a high concentration and has been proven to be an inorganic antioxidant that plays an important role in oxidative metabolism. Vanadium-dependent bromoperoxidases (vBPOs) and iodoperoxidases (vIPOs), which catalyze the oxidation of iodide, are essential for iodine accumulation and metabolism. Heavy metal pollutant cadmium (Cd) from anthropogenic activities can cause damage to algae mainly by producing oxidative stress. Here, the effects of iodine pretreatment on the stress of S. japonica caused by cadmium were analyzed. The growth experiment showed that iodine pretreatment could reduce the damage of low concentration cadmium on S. japonica young thalli. At the transcriptomic level, gene ontology (GO) enrichment analysis confirmed that cadmium stress could cause a peroxidation reaction in S. japonica. However, the most significant GO term was "photosystem I" in the series with iodine pretreatment. Weighted gene co-expression network analysis (WGCNA) indicated that iodine pretreatment alleviated cadmium stress responses of S. japonica by affecting the photosynthesis process. Analysis of the differentially expressed genes (DEGs) showed that five enzymes from the vBPO family and 13 enzymes from the vIPO family might play crucial roles in this process.

Keywords: Saccharina japonica; cadmium stress; iodine; transcriptome; vHPOs.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Comparison of morphological and physiological properties of Saccharina japonica sporophytes exposed to different concentrations of cadmium (C00, C01, C05, C20 for 0, 1, 5, 20 mg L−1 groups) for five days after 10 mg L−1 iodine pretreatment for 48 h (I10) or no pretreatment (I00). (a) Morphological characteristics. (b) Relative growth rate (RGR) for length. (c) RGR for fresh weight. (d) Maximum quantum yield of photosystem II (Fv/Fm). The data are the mean of triplicates. Vertical bars indicate standard deviations. Different letters indicate statistically significant differences (p < 0.05).
Figure 2
Figure 2
Gene ontology (GO) analysis of trending genes under increased concentrations of cadmium stress after iodine pretreatment (I10) or no pretreatment (I00). (a) GO analysis of 4258 trending genes in the I00 series. (b) GO analysis of the trending genes in the I00 series according to p-values. (c) GO analysis of 4123 trending genes in the I10 series. (d) GO analysis of the trending genes in the I10 series according to p-values.
Figure 3
Figure 3
Gene ontology (GO) analysis of down-regulated genes (profile 0) under increased concentrations of cadmium stress after iodine pretreatment (I10) or no pretreatment (I00). (a) GO analysis of 850 down-regulated genes (profile 0) in the I00 series. (b) GO analysis of 273 down-regulated genes (profile 0) in the I10 series.
Figure 4
Figure 4
Differentially expressed genes (DEGs) among different treatment groups. (a) Number of DEGs identified in pairwise comparisons. (b) Venn diagram showing the common and specific DEGs in the three representative couples. (c) Kyoto encyclopedia of genes and genomes (KEGG) analysis of DEGs between I00C00 and I00C20. (d) KEGG analysis of DEGs between I10C00 and I10C20. (e) KEGG analysis of DEGs between I00C20 and I10C20.
Figure 5
Figure 5
Module–trait correlations, gene expression patterns, and Kyoto encyclopedia of genes and genomes (KEGG) analysis of eigengenes in the “black” module correlated with relative growth rate (RGR) for length and maximum quantum yield of photosystem II (Fv/Fm). (a) Correlation of the modules with traits under different cadmium stresses after iodine pretreatment or no pretreatment and corresponding p values. Red and green colors denote positive and negative correlation, respectively. (b) Expression patterns of the “black” module, which highly correlated with RGR and Fv/Fm. (c) KEGG annotation of genes in the “black” module.
Figure 6
Figure 6
Reverse transcription quantitative PCR (RT-qPCR) validation of the expression levels of the 10 selected differentially expressed genes (DEGs) (a–j). RNA-seq and RT-qPCR data are indicated in blue and orange, respectively. HP1, HP2, and HP3 indicate I00C20-vs-I00C00, I10C20-vs-I10C00, and I10C20-vs-I00C20, respectively.
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