Soybean steroids improve crop abiotic stress tolerance and increase yield

Abstract

Sterols have long been associated with diverse fields, such as cancer treatment, drug development, and plant growth; however, their underlying mechanisms and functions remain enigmatic. Here, we unveil a critical role played by a GmNF-YC9-mediated CCAAT-box transcription complex in modulating the steroid metabolism pathway within soybeans. Specifically, this complex directly activates squalene monooxygenase (GmSQE1), which is a rate-limiting enzyme in steroid synthesis. Our findings demonstrate that overexpression of either GmNF-YC9 or GmSQE1 significantly enhances soybean stress tolerance, while the inhibition of SQE weakens this tolerance. Field experiments conducted over two seasons further reveal increased yields per plant in both GmNF-YC9 and GmSQE1 overexpressing plants under drought stress conditions. This enhanced stress tolerance is attributed to the reduction of abiotic stress-induced cell oxidative damage. Transcriptome and metabolome analyses shed light on the upregulation of multiple sterol compounds, including fucosterol and soyasaponin II, in GmNF-YC9 and GmSQE1 overexpressing soybean plants under stress conditions. Intriguingly, the application of soybean steroids, including fucosterol and soyasaponin II, significantly improves drought tolerance in soybean, wheat, foxtail millet, and maize. These findings underscore the pivotal role of soybean steroids in countering oxidative stress in plants and offer a new research strategy for enhancing crop stress tolerance and quality from gene regulation to chemical intervention.

Keywords: abiotic stress; plant steroid hormone; regulated mechanism; soybean (Glycine max); squalene monooxygenase.

Figure 1

Stress tolerance analysis of GmNF‐YC9 overexpressing soybean plants. (a) Phenotype analysis of 7‐day‐old WT and GmNF‐YC9‐OE soybean seedling plants after 7 days of different stress treatments. (b–d) Total root length (b), hypocotyl (c), and fresh weight (d) analysis of 7‐day‐old WT and GmNF‐YC9‐OE soybean plants after 7 days of different stress treatments. (e) The different slice samples of the root tip elongation zone after 7 days of 200 mM mannitol treatment. (f) The percentage of different types of root tip slice samples. (g) Phenotypic analysis of GmNF‐YC9‐OE and WT plants at seedling stage under drought and salt stress conditions. (h, i) Proline (h) and MDA (i) content analysis of GmNF‐YC9‐OE and WT plants at seedling stage under drought and salt stress conditions. (j) The fresh weight of GmNF‐YC9‐OE and WT plants at seedling stage under drought and salt stress conditions.

Figure 2

Interaction verification of GmNF‐YC9 and its candidate proteins. (a–j) Interaction verification between GmNF‐YC9 and its candidate proteins (GmNF‐YB24 and GmNF‐YA2) by yeast two‐hybrid (a), BiFC (b–d), LCI (e–g), and pull‐down (h–j) assays. YB24 and NF‐YB24, GmNF‐YB24; YA2 and NF‐YA2, GmNF‐YA2; YC9 and NF‐YC9, GmNF‐YC9.

Figure 3

Downstream target gene and its regulation pathway analysis of GmNF‐YC9 transcription factor. (a) The Venn diagram shows gene co‐expression analysis of WT and GmNF‐YC9‐OE soybean plants under drought conditions. (b) GO enrichment analysis of differentially expressed genes (DEGs) in GmNF‐YC9‐OE soybean plants. Red asterisk indicates squalene monooxygenase (GmSQE1). (c, d) Interaction analysis between the NF‐Y transcription factor and GmSQE1 promoter by LUC activity assay. (e) The module of SQE‐mediated catalysation to squalene. (f) Phenotype analysis of 7‐day‐old soybean seedling plants after 10 days of SQ (600 μg/L), 2,3‐OSQ (300 μg/L), mannitol (200 mM), and terbinafine (100 μM) treatments, respectively. (g, h) Total root length (g) and fresh weight (h) of soybean seedlings under different treatments. (i) The inhibition of terbinafine on SQE‐mediated catalysation to SQ. (j) Phenotype of 7‐day‐old soybean seedlings after 10 days of 100 mM NaCl, 100 mM mannitol, and 25 μM terbinafine treatments. (k–n) Fresh weight (k, l) and total root length (m, n) of 7‐day‐old soybean seedlings after 10 days of 100 mM NaCl, 100 mM mannitol, and 25 μM terbinafine treatment conditions. (o) Squalene content analysis of soybean seedling roots under different treatment conditions (25 μM terbinafine and 100 mM mannitol). (p, q) Cycloartenol (p) and beta‐amyrin (q) content analysis of soybean seedling roots under 100 mM mannitol treatment conditions. AM, beta‐amyrin; CY, cycloartenol.

Figure 4

Stress tolerance identification analysis of GmSQE1 overexpressing soybean plants. (a) Phenotype of WT and GmSQE1‐OE seedling soybean plants under drought and 200 mM NaCl treatment conditions. (b) Proline, MDA, and chlorophyll content analysis of WT and GmSQE1‐OE soybean plants under different stress conditions. (c) Phenotype analysis of GmSQE1‐OE soybean plants at adult stage under drought conditions in the field in the year 2020. (d, e) Phenotype (d) and relative content (e) of different seed types in GmSQE1‐OE soybean plants under drought conditions in the field in the year 2020. (f) Phenotype analysis of GmSQE1‐OE soybean plants at adult stage under drought conditions in the field in the year 2021. (g) Relative contents of different seed types in GmSQE1‐OE soybean plants under drought conditions in the field in the year 2021. (h–l) Agronomic trait analysis of WT and GmSQE1‐OE soybean plants under drought conditions in the field in the year 2021. (m) Oxidative stress tolerance analysis of GmSQE1 transgenic soybean plants under 50 μM MV treatment. (n) Fresh weight analysis of GmSQE1 transgenic soybean plants under 50 μM MV treatment. (o) Oxidative stress tolerance analysis of GmNF‐YC9 transgenic soybean plants under 50 μM MV treatment. (p) Fresh weight analysis of GmNF‐YC9 transgenic soybean plants under 50 μM MV treatment. (q, r) 200 mM H₂O₂‐induced cell death analysis of GmSQE1 (q) and GmNF‐YC9 (r) transgenic soybean plant roots by Pi staining.

Figure 5

Differentially accumulated sterol metabolite analysis in WT, GmNF‐YC9‐OE, and GmSQE1‐OE soybean plants under drought stress conditions using transcriptome and metabolome. (a) Analysis of differentially expressed genes (DEGs) between GmNF‐YC9‐OE and WT plants under drought stress conditions using transcriptome technology. (b) Analysis of differentially accumulated metabolites (DAMs) between GmNF‐YC9‐OE and WT plants under drought stress conditions using metabolome technology. (c) Correlation analysis of drought stress‐induced transcriptome and metabolome data of GmNF‐YC9‐OE vs WT. (d) KEGG pathway correlation analysis of transcriptome and metabolome in GmNF‐YC9‐OE vs WT plants under drought stress conditions. (e) Correlation analysis of metabolome data among GmNF‐YC9‐OE, GmSQE1‐OE, and WT plants under drought stress conditions. (f) Analysis of plant SQE‐mediated catalysed pathways. As SQE catalysis is the rate‐limiting step in triterpenoid, steroid and steroid derivative biosynthesis, we focused on these compound classes. (g) Differentially expressed steroid and their derivative analysis among GmNF‐YC9‐OE, GmSQE1‐OE, and WT plants under drought stress conditions. (h) Differentially expressed triterpenoid analysis among GmNF‐YC9‐OE, GmSQE1‐OE, and WT plants under drought stress conditions. The green hexagon in figure g and h indicates the accumulations of 9 steroid‐related compounds and 14 triterpenoids in both GmNF‐YC9‐OE and GmSQE1‐OE plants under drought stress conditions. The red pentacle in figure g and h indicates the significant accumulations of steroid‐related compounds and triterpenoids in both GmNF‐YC9‐OE and GmSQE1‐OE plants under drought stress conditions.

Figure 6

Function analysis of fucosterol and soyasaponin II in plant. (a, b) Phenotype (a) and biomass (b) analysis of soybean seedling plants under high concentrations of fucosterol and soyasaponin II treatment conditions. In figure a and b, HF indicates a high concentration of fucosterol (5 mg/L), while HS indicates a high concentration of soyasaponin II (5 mg/L). (c, d) Phenotype (c) and biomass (d) analysis of soybean seedling plants under moderate concentrations of fucosterol and soyasaponin II treatment conditions. (e–g) Phenotype (e), biomass (f), and proline (Pro) content (g) analysis of soybean seedling plants under fucosterol, soyasaponin II, and 100 mM NaCl treatment conditions. In figure e–g, N indicates 100 mM NaCl. (h–j) Phenotype (h), biomass (i), and proline (Pro) content (j) analysis of soybean seedling plants under fucosterol, soyasaponin II, and mannitol treatment conditions. In figure h–j, M indicates 100 mM mannitol. (k) Phenotype analysis of soybean, wheat, and foxtail millet plants by spraying moderate concentration of fucosterol and soyasaponin II under drought conditions. (l, m) MDA (l) and proline (Pro) content (m) analysis of soybean, wheat, and foxtail millet plants by spraying moderate concentration of fucosterol and soyasaponin II under drought conditions. In figure c–k, LF indicates a moderate concentration of fucosterol (300 μg/L), while LS indicates a moderate concentration of soyasaponin II (300 μg/L).

Figure 7

The model of NF‐Y‐SQE module and soybean steroids improving plant stress tolerance. NF‐Y‐SQE module participates in regulating plant stress tolerance by enhancing SQE‐mediated squalene metabolic pathways. Application of plant steroids or triterpenoids in crops enhanced their tolerance to drought stress.