Transcriptome Analysis Reveals the Stress Tolerance Mechanisms of Cadmium in Zoysia japonica

Abstract

Cadmium (Cd) is a severe heavy metal pollutant globally. Zoysia japonica is an important perennial warm-season turf grass that potentially plays a role in phytoremediation in Cd-polluted soil areas; however, the molecular mechanisms underlying its Cd stress response are unknown. To further investigate the early gene response pattern in Z. japonica under Cd stress, plant leaves were harvested 0, 6, 12, and 24 h after Cd stress (400 μM CdCl₂) treatment and used for a time-course RNA-sequencing analysis. Twelve cDNA libraries were constructed and sequenced, and high-quality data were obtained, whose mapped rates were all higher than 94%, and more than 601 million bp of sequence were generated. A total of 5321, 6526, and 4016 differentially expressed genes were identified 6, 12, and 24 h after Cd stress treatment, respectively. A total of 1660 genes were differentially expressed at the three time points, and their gene expression profiles over time were elucidated. Based on the analysis of these genes, the important mechanisms for the Cd stress response in Z. japonica were identified. Specific genes participating in glutathione metabolism, plant hormone signal and transduction, members of protein processing in the endoplasmic reticulum, transporter proteins, transcription factors, and carbohydrate metabolism pathways were further analyzed in detail. These genes may contribute to the improvement of Cd tolerance in Z. japonica. In addition, some candidate genes were highlighted for future studies on Cd stress resistance in Z. japonica and other plants. Our results illustrate the early gene expression response of Z. japonica leaves to Cd and provide some new understanding of the molecular mechanisms of Cd stress in Zosia and Gramineae species.

Keywords: Zoysia japonica; cadmium; differentially expressed genes; molecular mechanism; transcriptome.

Figure 1

The profile of differentially expressed genes at different time points. (A) Volcano plot of the L_6 h vs. L_0 h group; (B) Volcano plot of the L_12 h vs. L_0 h group; (C) Volcano plot of the L_24 h vs. L_0 h group; (D) Venn diagram for all differentially expressed genes.

Figure 2

Expression profiles of the common genes at different time points. (A) Heatmap of all differentially expressed genes; (B) cluster analysis of differentially expressed gene profiles.

Figure 3

The GO and KEGG enrichment analysis of commonly expressed genes. (A) GO analysis; (B) KEGG enrichment analysis.

Figure 4

Expression profiles of commonly expressed genes related to glutathione metabolism, plant hormone signal and transduction, and transcription regulation pathways. (A) Glutathione metabolism pathway; (B) plant hormone signal and transduction pathway; (C) Protein processing in endoplasmic reticulum pathway.

Figure 5

Expression profiles of common expressed genes related to transportation and protein processing in endoplasmic reticulum pathway. (A) Transporter protein genes; (B) transcription factor.

Figure 6

A simple diagram associated with the Cd tolerance mechanism in Z. japonica leaves. Basic helix–loop–helix transcription factors, bHLH; adenine nucleotide transporter, BT1; probable mitochondrial adenine nucleotide transporter, BTL1; Equilibrative nucleotide transporter 3, ENT3; ethylene-responsive transcription factors, ERFs; Sugar transporter ERD6-like, ERD6-like; Folate transporter 1, FOLT1; eIF-2-alpha kinase, GCN2; heat stress transcription factors, HSFs; ICE-like transcription factor, ICE; dihydrolipoyllysine-residue acetyltransferase component 4 of the pyruvate dehydrogenase complex, LTA2; MADS-box transcription factor, MADS; organic cation/carnitine transporter 3, OCT3; oligopeptide transporter 1, OPT1; protein disulfide isomerase, PDI; probable ubiquitin receptor, RAD23; sugar transport protein 14, STP14; dolichyl-diphosphooligosaccharide-protein glycosyltransferase subunit, STT3B; probable metal-nicotianamine transporters, YSLs.

Figure 7

Validation of RNA-seq results with qRT-PCR.