Transcriptomic and Metabolomic Analyses Reveal the Differential Regulatory Mechanisms of Compound Material on the Responses of Brassica campestris to Saline and Alkaline Stresses

Abstract

Oilseed rape not only has the function of improve saline and alkaline soils, but also alleviate the local feed shortage. However, medium- and high-degree soil salinization and alkalinization always inhibit the growth of oilseed rape. Studies have shown that compound material can improve the tolerance to saline and alkaline stress of crops, but the difference in the regulation mechanism of compound material on oilseed rape in saline and alkaline soils is not clear. This study explored the difference through determining the leaf ion contents, physiological indexes, transcriptomics, and metabolomics of oilseed rape in salinized soil (NaCl 8 g kg^-1) and alkalinized soil (Na₂CO₃ 8 g kg^-1) at full flowering stage, respectively after the application of compound material. The results showed that in salinized and alkalinized soil, the compound material upregulated the genes related to the regulation of potassium ion transport, and changed the amino acid metabolic pathway, which reduced the contents of Na⁺, malondialdehyde (MDA), and relative conductivity (REC) in leaves, and increased the contents of K⁺ and Mg²⁺ and the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). However, there were differences in the regulation mechanism of compound material in salinized and alkalinized soil. In salinized soil, the compound material improved the tolerance of oilseed rape to saline stress by upregulating transcription factors mannose-1-phosphate guanylyltransferase (GPMM) and Glutamine--fructose-6-phosphate transaminase (GFPT) and downregulating phosphomannomutase (PMM) to change nucleotide metabolism pathway and lipid metabolism pathway. In alkalized soil, the compound material improved the tolerance of oilseed rape to alkaline stress by upregulating transcription factors Phenylalanine ammonia lyase (PAL) to change the biosynthesis pathway of other secondary metabolites. Therefore, the compound material can improve the tolerance of oilseed rape to saline and alkaline stress by regulating the genetic adaptability and apparent plasticity, but the mechanisms were different. This study provides a practical method for the ecological environment restoration and the development of animal husbandry.

Keywords: animal husbandry; biosynthesis of other secondary metabolites; forage crop; genetic adaptability; saline–alkali land development.

Figure 1

Changes in ion content (K⁺, Na⁺, K⁺/Na⁺ ratio, Ca²⁺, Mg²⁺, ${\mathrm{SO}}_4^{2-}$, Cl⁻, and ${\mathrm{HCO}}_3^{-}$) in Brassica campestris leaves in different treatments (A), and changes in antioxidant enzymes activity and the content of MDA and REC in Brassica campestris leaves in different treatments (B). Different lowercase letters indicate significant difference at p < 0.05.

Figure 2

Heatmap of correlations among samples in different treatments (A), PCA analysis (B), the number of DEGs in leaves identified in different treatments by transcriptomic analysis (C), and Venn diagram of DEGs (D).

Figure 3

GO enrichment analysis. The top ten enriched GO terms for NaCl treatments (YCK and YP treatment; A), the top ten enriched GO terms for Na₂CO₃ treatments (JCK and JP treatment; B), the top ten enriched GO terms for the control (YCK and JCK treatment; C), and the top ten enriched GO terms for compound material treatments (YP and JP treatment; D). BP, CC, and MF represent biological process, cellular component, and molecular function, respectively. *Indicates significant difference at p < 0.05.

Figure 4

Analysis of metabolites of Brassica campestris in different treatments. (A) Heat map of metabolites. The content of each metabolite was normalized to complete linkage hierarchical clustering. Each treatment was shown in a column, and each metabolite was represented by a row. Red indicates high abundance, and green indicates low abundance. (B) Principal component analysis of metabolites. (C) The number of DEMs upregulated and downregulated in different treatments. (D) Venn diagram of DEMs and classification.

Figure 5

Metabolic pathways and the mutual regulation relationships in different treatments. The pathway notes and arrows in different colors represent the regulation pathways for different treatments. Red represents the common regulation pathway of NaCl treatments (YCK and YP treatment) and Na₂CO₃ treatments (JCK and JP treatment), yellow represents the regulation pathway of NaCl treatments (YCK and YP treatment), and blue represents the regulation pathway of Na₂CO₃ treatments (JCK and JP treatment). The ellipse indicates the obviously changed transcription factors, and the bold font indicates the differentially expressed metabolites (DEMs). The data in the box represents the average expression of metabolites for the two treatments (log2FC), in which red indicates upregulation, and blue indicates downregulation.

Figure 6

Co-occurrence network of phenotype, physiological indexes, ion contents, differential expressed genes, and differential expressed metabolites of Brassica campestris. (A) YCK treatment, (B) JCK treatment, (C) YP treatment, and (D) JP treatment. There are positive or negative correlations between the two indexes connected (p < 0.05). The indexes with connectivity greater than 15 are marked with words.

Figure 7

Regulation mechanisms of compound material on the responses of Brassica campestris of compound material to saline and alkaline stresses of Brassica campestris. Yellow and blue represent the regulation mechanisms of the responses to saline stress and alkaline stress, respectively, and green represents the common regulation mechanism of the responses to saline stress and alkaline stress. Red indicates upregulation, and blue indicates downregulation.