Comparative Analysis of Salt Tolerance and Transcriptomics in Two Varieties of Agropyron desertorum at Different Developmental Stages

Abstract

Background: Most of the grasslands in China are experiencing varying degrees of degradation, desertification, and salinization (collectively referred to as the "three degradations"), posing a serious threat to the country's ecological security. Agropyron desertorum, known for its wide distribution, strong adaptability, and resistance, is an excellent grass species for the ecological restoration of grasslands affected by the "three degradations". This study focused on two currently popular varieties of A. desertorum, exploring their salt tolerance mechanisms and identifying candidate genes for salt and alkali tolerance.

Methods: Transcriptome sequencing was performed on two varieties of A. desertorum during the seed germination and seedling stages under varying degrees of saline-alkali stress. At the seed stage, we measured the germination rate, relative germination rate, germination index, and salt injury rate under different NaCl concentrations. During the seedling stage, physiological indicators, including superoxide dismutase (SOD), peroxidase (POD), malondialdehyde (MDA), proline (PRO), soluble protein (SP), and catalase (CAT), were analyzed after exposure to 30, 60, 120, and 180 mM NaCl for 12 days. Analysis of differentially expressed genes (DEGs) at 6 and 24 h post-treatment with 120 mM NaCl revealed significant differences in the salt stress responses between the two cultivars.

Results: Our study indicates that during the seed stage, A. desertorum (Schult.) exhibits a higher relative germination potential, relative germination rate, and relative germination index, along with a lower relative salt injury rate compared to A. desertorum cv. Nordan. Compared with A. desertorum cv. Nordan, A. desertorum (Schult.) has higher salt tolerance, which is related to its stronger antioxidant activity and different antioxidant-related pathways. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were used to identify the key biological processes and pathways involved in salt tolerance, including plant hormone signal transduction, antioxidant defense, and cell membrane stability.

Conclusions: A. desertorum (Schult.) exhibits stronger salt tolerance than A. desertorum cv. Nordan. Salt stress at a concentration of 30-60 mM promotes the germination of the seeds of both Agropyron cultivars. The two Agropyron plants mainly overcome the damage caused by salt stress through the AsA-GSH pathway. This study provides valuable insights into the molecular mechanisms of salt tolerance in Agropyron species and lays the groundwork for future breeding programs aimed at improving salt tolerance in desert grasses.

Keywords: Agropyron desertorum; RNA-seq; physiological analysis; salt stress; seed germination; transcriptomics.

Figure 1

A. desertorum plant varieties. (A) A. desertorum (Fisch.) Schult single-plant picture. (B) A. desertorum (Fisch.) Schult. cv. Nordan single-plant picture. (C) Comparison of two varieties of Agropyron. (D) A. desertorum (Fisch.) Schult reproductive branch picture. (E) A. desertorum (Fisch.) Schult leaf picture. (F) A. desertorum (Fisch.) Schult stem picture. (G) A. desertorum (Fisch.) Schult flower spike, spikelet, and floret picture. (H) A. desertorum (Fisch.) Schult seed picture. Note: (C) The left side is A. desertorum (Fisch.) Schult and the right side is A. desertorum (Fisch.) Schult. cv. Nordan. (G) The left picture shows a spike, the top-right picture shows spikelets, and the bottom-right picture shows florets.

Figure 2

Pictures of the seedlings of two varieties of A. desertorum. (A) Pictures of A. desertorum (Fisch.) Schult. (B) Pictures of A. desertorum (Fisch.) Schult. cv. Nordan. Note: The NACL stress concentration was measured in mM.

Figure 3

Measurement of seed-stage parameters in two varieties. (A) Relative germination potential on day 7 for both varieties. (B–D) Relative germination rate, relative germination index, and relative salt injury rate under salt stress, respectively. Note: S: A. desertorum Schult; N: A. desertorum Nordan. The dotted line is regarded as the suitable range of salt tolerance of seeds. One-way ANOVA was performed for significance analysis. Each bar represents three biological replicates ± SD. Different lowercase letters ** indicate significant differences between groups (** p < 0.001).

Figure 4

Effects of salt stress on the phenotypic and physiological indicators of two varieties. (A–C) Leaf length, leaf width and root length of A. desertorum Schult and A. desertorum Nordan under salt stress. (D–I) Physiological parameters of S and N under salt stress, including SOD, POD, MDA, CAT, PRO, and SP, respectively, Note: S: A. desertorum Schult; N: A. desertorum Nordan. One-way ANOVA was performed for significance analysis. Each bar represents three biological replicates ± SD. Different lowercase letters indicate significant differences at p < 0.05. * and ** indicate significant differences between groups (* p < 0.05; ** p < 0.001).

Figure 5

Transcriptome data analysis. (A) A comprehensive summary of annotations for all transcripts across various databases was compiled. (B) Total number of upregulated and downregulated DEGs in A. desertorum Schult and A. desertorum Nordan at 6 h and 24 h compared with the control. (C) Venn diagram of all DEGs in A. desertorum Schult and A. desertorum Nordan at 6 h (S_6 and N_6) and 24 h (S_24, N_24). (D) Venn diagram of upregulated and downregulated DEGs in A. desertorum Schult and A. desertorum Nordan at 6 h (S_6, N_6) of salt stress. (E) Venn diagram of upregulated and downregulated DEGs in A. desertorum Schult and A. desertorum Nordan at 24 h (S_24, M_24) of salt stress.

Figure 6

KEGG pathway enrichment analysis of DEGs identified in A. desertorum Schult and A. desertorum Nordan.

Figure 7

Analysis and comparison of DEGs related to the ASA–GSH pathway in A. desertorum Schult and A. desertorum Nordan under salt stress. (A) Main ASA–GSH pathway under salt stress. (B) Heatmap of DEGs related to the ASA–GSH pathway in A. desertorum Schult and A. desertorum Nordan. For treatments (6 h and 24 h) and control (0 h), upregulated genes are shown in red and downregulated genes are shown in blue.