Soil salinization seriously restricts the growth and yield of soybeans. However, little information is available on the early growth stages of soybeans which are subjected to the gibberellin biosynthesis inhibitor, prohexadione-calcium (Pro-Ca). This study aimed to investigate the effects of exogenous Pro-Ca on saline-alkali stress-induced damages to photosynthesis and antioxidant defenses in soybean (Glycine max L.) seedlings. At the V3 growth stage, salt-tolerant genotype Hefeng 50 (HF50) and salt-sensitive genotype Kenfeng 16 (KF16) were subjected to 110 mmol L^-1 mixed saline-alkali stress respectively, and then 100 mg L^-1 Pro-Ca was sprayed on the leaves. Our results showed that saline-alkali stress accelerated the degradation of thylakoids, inhibited chlorophyll synthesis, reduced shoot dry weight, electron transfer rate (ETR), and peroxidase (POD) activity, the concentration of ascorbic acid (AsA) and soluble sugar, but enhanced the concentration of proline, hydrogen peroxide (H₂O₂) and the rate of superoxide radical (O₂^∙-) generation. Additionally, saline-alkali stress induced a lower decrease of the net photosynthetic rate (P_n), potential activity of PSII (F_v/F₀), and maximum quantum yield of PSII (F_v/F_m) in salt-tolerant HF50 than in salt-sensitive KF16. Nevertheless, foliar spraying of exogenous Pro-Ca increased the chlorophyll content, P_n, F_v/F₀, and F_v/F_m. These results were more prominent when Pro-Ca was applied to KF16 under saline-alkali conditions. Furthermore, exogenous application of Pro-Ca retarded the degradation of thylakoids, increased the ETR and the accumulation of AsA, soluble sugar, and proline, activated the activities of superoxide dismutase (SOD), catalase (CAT), and POD, and decreased the concentration of malondialdehyde (MDA), electrolyte leakage (EL), O₂^∙-, and H₂O₂. These results indicated that Pro-Ca could effectively protect soybean seedlings against damage from saline-alkali stress by regulating seedling phenotype, photosynthetic apparatus, antioxidant defense, and osmoregulation.

Salt stress is a major factor limiting the growth and yield of soybean (Glycine max). Wild soybeans (Glycine soja) contain high allelic diversity and beneficial alleles that can be re-introduced into domesticated soybeans to improve adaption to the environment. However, very few beneficial alleles have been identified from wild soybean. Here, we demonstrate that wild soybean is more salt tolerant than cultivated soybean and examine dehydration responsive element-binding (DREB) family transcription factor genes to look for advantageous alleles that might improve drought tolerance in cultivated soybean. Our genome-wide analysis identified 103 DREB genes from the Glycine max genome. By combined RNA-sequencing and population genetics of wild, landrace, and cultivated soybean accessions, we show that the natural variation in DREB3a and DREB3b is related to differences in salt tolerance in soybean accessions. Interestingly, DREB3b, but not DREB3a, appears to have undergone artificial selection. Soybean plants carrying the wild soybean DREB3b allele (DREB3b^39Del) are more salt tolerant than those containing the reference genome allele (DREB3b^Ref). Together, our results suggest that the loss of the DREB3b^39Del allele through domestication of cultivated soybean may be associated with a reduction in salt tolerance. Our findings provide crucial information for improving salt tolerance in soybean through molecular breeding.

Brassinolide (BR) is a sterol compound, which can regulate plant seed germination, flowering, senescence, tropism, photosynthesis, stress resistance, and is closely related to other signaling molecules. This study aimed to evaluate the ability of soaking with BR to regulate growth quality at rice seedling stage under salt stress. Results demonstrated that salt stress increases the contents of ROS, MDA, Na⁺ and ABA, reduces the the SPAD value, net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), maximum fluorescence (Fm), variable fluorescence (Fv), the effective photochemical efficiency of PSII (Fv/Fo) and the maximum photochemical efficiency of PSII (Fv/Fm), reduces the biomass production and inhabits plant growth. All of these responses were effectively alleviated by BR soaking treatment. Soaking with BR could increase the activities of superoxide dismutase, peroxidase, catalase, ascorbate peroxidase, and the contents of ascorbic acid, glutathione as well as soluble protein and proline, while BR soaking treatment inhibited the accumulation of ROS and reduced the content of MDA. BR soaking significantly reduced the contents of Na⁺ and increased the contents of K⁺ and Ca²⁺, indicating that soaking with BR is beneficial to the excretion of Na⁺, the absorption of K⁺ and Ca²⁺ and the maintenance of ion balance in rice seedlings under salt stress. BR also maintained endogenous hormone balance by increasing the contents of indoleacetic acid (IAA), zeatin (ZT), salicylic acid (SA), and decreasing the ABA content. Soaking with BR significantly increased the SPAD value, Pn and Tr and enhanced the Fm, Fv/Fm and Fv/Fo of rice seedlings under NaCl stress, protected the photosythetic system of plants, and improved their biomass. It is suggested that BR was beneficial to protect membrane lipid peroxidation, the modulation of antioxidant defense systems, ion balance and endogenous hormonal balance with imposition to salt stress.

Background: Chilling injury of mung bean (Vigna radiata (L.)) during the blooming and podding stages is a major agricultural threat in Northeast China. Uniconazole (UNZ) can alleviate water deficit stress in soybean and waterlogging stress in mung bean. However, there has been no report on the effect of UNZ application on the growth and transcriptomic profile of mung bean under chilling stress. Results: UNZ application before chilling stress at the R1 stage alleviated the decline in mung bean yield. UNZ delayed the decrease in leaf chlorophyll content under chilling stress at the R1 stage and accelerated the increase in leaf chlorophyll content during the recovery period. Eighteen separate RNA-Seq libraries were generated from RNA samples collected from leaves exposed to six different treatment schemes. The numbers of DEGs specific for UNZ treatment between D1 + S vs. D1 and D4 + S vs. D4 were 708 and 810, respectively. GO annotations showed that photosynthesis genes were obviously enriched among the genes affected by chilling stress and UNZ application. KEGG pathway enrichment analysis indicated that 4 pathways (cutin, suberin and wax biosynthesis; photosynthesis; porphyrin and chlorophyll metabolism; and ribosome) were downregulated, while plant–pathogen interaction was upregulated, by chilling stress. UNZ application effectively prevented the further downregulation of the gene expression of members of these 4 KEGG pathways under chilling stress. Conclusions: UNZ application effectively delayed the decrease in photosynthetic pigment content under chilling stress and accelerated the increase in photosynthetic pigment content during the recovery period, thus effectively limiting the decline in mung bean yield. UNZ application effectively prevented the further downregulation of the gene expression of members of 4 KEGG pathways under chilling stress and increased mung bean tolerance to chilling stress.

Continuous cropping stress involves such factors as biological barriers, allelopathic autotoxicity, deterioration of soil physicochemical properties, and soil fertility imbalance and is regarded as a kind of comprehensive stress limiting soybean yield and quality. Genomic DNA methylation is an important regulatory mechanism for plants to resist various environmental stresses. Therefore, it is especially worthwhile to reveal genomic methylation characteristics under stress and clarify the relationship between DNA methylation status and continuous cropping stress adaptability in soybean. We generated a genome-wide map of cytosine methylation induced by this kind of comprehensive stress in a tolerant soybean variety (Kang Xian 2, KX2) and a sensitive variety (He Feng, HF55) using whole-genome bisulfite sequencing (WGBS) technology. The expression of DNA demethylase genes was detected using real-time quantitative PCR (qRT-PCR). The functions of differentially methylated genes (DMGs) involved in stress response in biochemical metabolism and genetic information transmission were further assessed based on Gene Ontology (GO) annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis. The results showed that genomic DNA demethylation was closely related to continuous cropping comprehensive stress adaptability in soybean, which was further verified by the increasing expression of DNA demethylases ROS1 and DML. The demethylation of mCpG and mCpHpG (mCpApG preferred) contexts was more critical, which mainly occurred in gene-regulatory regions at the whole-chromosome scale. Moreover, this kind of stress adaptability may be related to various stress responders generated through strengthened glucose catabolism and amino acid and fatty acid anabolism, as well as fidelity transmission of genetic information. Genomic DNA demethylation was closely associated with continuous cropping comprehensive stress adaptability, highlighting the promising potential of screening continuous cropping-tolerant cultivars by DNA methylation index and further exploring the application of DNA demethylases in soybean breeding.

Extreme high temperature at the meiosis stage causes a severe decrease in spikelet fertility and grain yield in rice. The rice variety grain size on chromosome 2 (GS2) contains sequence variations of OsGRF4 (Oryza sativa growth-regulating factor 4; OsGRF4^AA), escaping the microRNA miR396-mediated degradation of this gene at the mRNA level. Accumulation of OsGRF4 enhances nitrogen usage and metabolism, and increases grain size and grain yield. In this study, we found that pollen viability and seed-setting rate under heat stress (HS) decreased more seriously in GS2 than in its comparator, Zhonghua 11 (ZH11). Transcriptomic analysis revealed that, following HS, genes related to carbohydrate metabolic processes were expressed and regulated differentially in the anthers of GS2 and ZH11. Moreover, the expression of genes involved in chloroplast development and photosynthesis, lipid metabolism, and key transcription factors, including eight male sterile genes, were inhibited by HS to a greater extent in GS2 than in ZH11. Interestingly, pre-mRNAs of OsGRF4, and a group of essential genes involved in development and fertilization, were differentially spliced in the anthers of GS2 and ZH11. Taken together, our results suggest that variation in OsGRF4 affects proper transcriptional and splicing regulation of genes under HS, and that this can be mediated by, and also feed back to, carbohydrate and nitrogen metabolism, resulting in a reduction in the heat tolerance of rice anthers.