Morpho-Physiochemical Indices and Transcriptome Analysis Reveal the Role of Glucosinolate and Erucic Acid in Response to Drought Stress during Seed Germination of Rapeseed

Abstract

The global expansion of rapeseed seed quality has been focused on maintaining glucosinolate (GSL) and erucic acid (EA) contents. However, the influence of seed GSL and EA contents on the germination process under drought stress remains poorly understood. Herein, 114 rapeseed accessions were divided into four groups based on GSL and EA contents to investigate their performance during seed imbibition under drought stress. Our results revealed significant variations in seed germination-related traits, particularly with higher GSL and EA, which exhibited higher germination % (G%) and lower mean germination time (MGT) under drought stress conditions. Moreover, osmoregulation, enzymatic system and hormonal regulation were improved in high GSL and high EA (HGHE) versus low GSL and low EA (LGLE) seeds, indicating the essential protective role of GSL and EA during the germination process in response to drought stress. The transcriptional regulation mechanism for coordinating GSL-EA-related pathways in response to drought stress during seed imbibition was found to involve the differential expression of sugar metabolism-, antioxidant-, and hormone-related genes with higher enrichment in HGHE compared to LGLE seeds. GO enrichment analysis showed higher variations in transcription regulator activity and DNA-binding transcription factors, as well as ATP and microtubule motor activity in GSL-EA-related pathways. Furthermore, KEGG analysis identified cellular processes, environmental information processing, and metabolism categories, with varied gene participation between GSL, EA and GSL-EA-related pathways. For further clarification, QY7 (LGLE) seeds were primed with different concentrations of GSL and EA under drought stress conditions. The results showed that 200 μmol/L of GSL and 400 μmol/L of EA significantly improved G%, MGT, and seedling fresh weight, besides regulating stress and fatty acid responsive genes during the seed germination process under drought stress conditions. Conclusively, exogenous application of GSL and EA is considered a promising method for enhancing the drought tolerance of LGLE seeds. Furthermore, the current investigation could provide a theoretical basis of GSL and EA roles and their underlying mechanisms in stress tolerance during the germination process.

Keywords: erucic acid; germination; glucosinolate; rapeseed; seed priming; transcriptome.

Figure 1

Variation effect of 114 rapeseed accessions at 12, 24, 36, 48 and 60 h of seed imbibition in terms of (A) germination%, (B) coefficient of variance (CV) and (C) mean germination time/day (MGT) under normal and drought stress conditions. Variation among the four seed type groups at 24 h in terms of (D) germination%, (E) coefficient of variance (CV) and (F) mean germination time/day (MGT) under normal and drought stress conditions. The different letters indicate significant differences at p < 0.05 using Duncan’s multiple range tests.

Figure 2

The effect of drought stress on (A) seed germination phenomena, (B) oil content, (C) total soluble sugar content, (D) total soluble protein content, (E) fructose-bisphosphate aldolase activity, and (F) phosphofructokinase activity during the seed germination in four seed type groups of rapeseed. Bars represent ±SE of three replicates. Asterisks indicate significant differences between drought and normal conditions, while asterisks with parentheses indicate significant differences between HGHE and the other three groups under drought conditions (ns: non-significant, * p < 0.05, ** p < 0.01; Student’s t-test).

Figure 3

The effect of drought stress on (A) seed ultrastructure, (B) ratio of protein-to-oil bodies area, (C) void area, (D) myrosinase activity, and (E) lipase activity during the seed germination in four seed type groups of rapeseed. Bars represent ±SE of three replicates. Asterisks indicate significant differences between drought and normal conditions, while asterisks with parentheses indicate significant differences between HGHE and the other three groups under drought conditions (ns: non-significant, * p < 0.05, ** p < 0.01; Student’s t-test).

Figure 4

The effect of drought stress on (A) malonaldehyde (MDA) content, (B) superoxide dismutase activity, (C) peroxidase activity, (D) catalase activity, (E) abscisic acid content, (F) gibberellic acid content, (G) salicylic acid content, and (H) indole acetic acid content during the seed germination in four seed type groups of rapeseed. Bars represent ±SE of three replicates. Asterisks indicate significant differences between drought and normal conditions, while asterisks with parentheses indicate significant differences between HGHE and other three groups under drought conditions (ns: non-significant, * p < 0.05, ** p < 0.01; Student’s t-test).

Figure 5

(A–C) Venn diagrams of the differential gene expression between four groups; (D) upset plot of the differential genes related to GSL and EA; (E–G) gene ontology (GO) annotation analysis of genes related to GSL, EA, and GSL–EA, respectively; and (H–J) Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of genes related to GSL, EA, and GSL–EA, respectively.

Figure 6

Representative DEGs involved in GSL-, EA-, and GSL–EA-related pathways; (A) glucose-; (B) myrosinase-; (C) lipid-; (D) antioxidant-; and (E) hormonal metabolism-related genes.

Figure 7

The influence of GSL and EA priming on (A,B) relative germination%, (C) seed germination phenomenon at 24 h of seed imbibition, (D,E) mean germination time, and (F,G) seedling fresh weight, respectively, in QY7 (LGLE) under normal and drought stress conditions during the germination and early seedling stage. Bars represent ±SE of three replicates. Asterisks indicate significant differences between drought and normal conditions, while asterisks with parentheses indicate significant differences between HP and different concentrations under drought conditions (ns: non-significant, * p < 0.05, ** p < 0.01; Student’s t-test).

Figure 8

The influence of seed priming via 200 μmol/L of GSL and 400 μmol/L of EA on the relative expression gene in QY7 (LGLE) at 24 h of seed imbibition under drought stress conditions. Bars represent ±SE of three replicates. Asterisks indicate significant differences between hydro-priming (HP) under normal conditions and treatment under drought conditions, while asterisks with parentheses indicate significant differences between HP and other treatments under drought conditions (ns: non-significant, ** p < 0.01; Student’s t-test).