N7 -SSPP fusion gene improves salt stress tolerance in transgenic Arabidopsis and soybean through ROS scavenging

Molecular Regulatory Network of Soybean Responses to Abiotic Stress

Global climate change exacerbates the impact of environmental stressors such as drought, salinity and extreme temperatures on crop growth and grain yield, endangering the sustainability of the food supply. Soybean (Glycine Max [L.] Merr.) is an important legume crop and plays a crucial role in the global food supply chain and food security, and contributes the substantial protein content relative to other crops. However, soybean yield stability is critically dependent on the plant's adaptive responses to abiotic stress factors, particularly drought, salinity and temperature extremes, which primarily impact its growth and productivity. Recently, various molecular techniques, including genetic engineering, transcriptomics, transcription factor analysis, CRISPR/Cas9, and conventional methods, have been employed to elucidate the molecular mechanisms of soybean responses to environmental stresses for the breeding of tolerant cultivars of soybean. This review summarises recent advances in dissecting the genetic factors and networks that contribute to soybean abiotic stress tolerance through diverse strategies. We also discuss future challenges and opportunities for the development of climate-resilient soybean varieties. Consequently, the updated review will serve as a comprehensive guideline for researchers investigating the genetic mechanism of abiotic stress in soybean.

Function of Nodulation-Associated GmNARK Kinase in Soybean Alkali Tolerance

Soybean (Glycine max) is a vital crop that is rich in high-quality protein and edible oil for human nutrition and agriculture. Saline-alkali stress, a severe environmental challenge, significantly limits soybean productivity. In this study, we found that the nodule receptor kinase GmNARK enhances soybean tolerance to alkali stress besides nodulation. GmNARK could be induced by alkali stress in soybean roots. Ectopic overexpression of the GmNARK gene in Arabidopsis could significantly improve plant tolerance to alkaline stress. Moreover, overexpression or silencing of the GmNARK gene in soybean hairy roots also enhanced composite soybean plant tolerance to alkaline stress on plates and in soils. Additionally, overexpression of the GmNARK gene upregulated expression levels of the genes that are involved in the reactive oxygen species (ROS) signaling pathways. These findings provide a critical theoretical basis for further elucidating the role of GmNARK kinase in salt-alkali resistance and lay a foundation for improving soybean productivity under salt-alkali stress.

An ABA biosynthesis enzyme gene OsNCED4 regulates NaCl and cold stress tolerance in rice

Rice (Oryza sativa L.) is susceptible to various abiotic stresses, such as salt, cold, and drought. Therefore, there is an urgent need to explore the relevant genes that enhance tolerance to these stresses. In this study, we identified a gene, OsNCED4 (9-cis-epoxycarotenoid dioxygenase 4), which regulates tolerance to multiple abiotic stresses. OsNCED4 encodes a chloroplast-localized abscisic acid (ABA) biosynthetic enzyme. The expression of OsNCED4 gene was significantly induced by 150 mM NaCl and cold stress. Disruption of OsNCED4 by CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats)/Cas9-mediated mutagenesis resulted in significant sensitivity to NaCl and cold stress. The salt and cold sensitivity of osnced4 mutant was due to the reduction of ABA content and the excessive accumulation of reactive oxygen species (ROS) under stress. Moreover, OsNCED4 also regulates drought stress tolerance of rice seedlings. Taken together, these results indicate that OsNCED4 is a new regulator for multiple abiotic stress tolerance in rice, and provided a potential target gene for enhancing multiple stress tolerance in the future.

Poplar glutathione S-transferase PtrGSTF8 contributes to reactive oxygen species scavenging and salt tolerance

Glutathione S-transferases (GSTs) constitute a protein superfamily encoded by a large gene family and play a crucial role in plant growth and development. However, their precise functions in wood plant responses to abiotic stress are not fully understood. In this study, we isolated a Phi class glutathione S-transferase-encoding gene, PtrGSTF8, from poplar (Populus alba × P. glandulosa), which is significantly up-regulated under salt stress. Moreover, compared with wild-type (WT) plants, transgenic tobacco plants exhibited significant salt stress tolerance. Under salt stress, PtrGSTF8-overexpressing tobacco plants showed a significant increase in plant height and root length, and less accumulation of reactive oxygen species. In addition, these transgenic tobacco plants exhibited higher superoxide dismutase, peroxidase, and catalase activities and reduced malondialdehyde content compared with WT plants. Quantitative real-time PCR experiments showed that the overexpression of PtrGSTF8 increased the expression of numerous genes related to salt stress. Furthermore, PtrMYB108, a MYB transcription factor involved in salt resistance in poplar, was found to directly activate the promoter of PtrGSTF8, as demonstrated by yeast one-hybrid assays and luciferase complementation assays. Taken together, these findings suggest that poplar PtrGSTF8 contributes to enhanced salt tolerance and confers multiple growth advantages when overexpressed in tobacco.

A novel PGPR strain, Streptomyces lasalocidi JCM 3373T, alleviates salt stress and shapes root architecture in soybean by secreting indole-3-carboxaldehyde

While soybean (Glycine max L.) provides the most important source of vegetable oil and protein, it is sensitive to salinity, which seriously endangers the yield and quality during soybean production. The application of Plant Growth-Promoting Rhizobacteria (PGPR) to improve salt tolerance for plant is currently gaining increasing attention. Streptomycetes are a major group of PGPR. However, to date, few streptomycetes has been successfully developed and applied to promote salt tolerance in soybean. Here, we discovered a novel PGPR strain, Streptomyces lasalocidi JCM 3373T, from 36 strains of streptomycetes via assays of their capacity to alleviate salt stress in soybean. Microscopic observation showed that S. lasalocidi JCM 3373T does not colonise soybean roots. Chemical analysis confirmed that S. lasalocidi JCM 3373T secretes indole-3-carboxaldehyde (ICA1d). Importantly, IAC1d inoculation alleviates salt stress in soybean and modulates its root architecture by regulating the expression of stress-responsive genes GmVSP, GmPHD2 and GmWRKY54 and root growth-related genes GmPIN1a, GmPIN2a, GmYUCCA5 and GmYUCCA6. Taken together, the novel PGPR strain, S. lasalocidi JCM 3373T, alleviates salt stress and improves root architecture in soybean by secreting ICA1d. Our findings provide novel clues for the development of new microbial inoculant and the improvement of crop productivity under salt stress.

Functional screening of the Arabidopsis 2C protein phosphatases family identifies PP2C15 as a negative regulator of plant immunity by targeting BRI1-associated receptor kinase 1

Genetic engineering using negative regulators of plant immunity has the potential to provide a huge impetus in agricultural biotechnology to achieve a higher degree of disease resistance without reducing yield. Type 2C protein phosphatases (PP2Cs) represent the largest group of protein phosphatases in plants, with a high potential for negative regulatory functions by blocking the transmission of defence signals through dephosphorylation. Here, we established a PP2C functional protoplast screen using pFRK1::luciferase as a reporter and found that 14 of 56 PP2Cs significantly inhibited the immune response induced by flg22. To verify the reliability of the system, a previously reported MAPK3/4/6-interacting protein phosphatase, PP2C5, was used; it was confirmed to be a negative regulator of PAMP-triggered immunity (PTI). We further identified PP2C15 as an interacting partner of BRI1-associated receptor kinase 1 (BAK1), which is the most well-known co-receptor of plasma membrane-localized pattern recognition receptors (PRRs), and a central component of PTI. PP2C15 dephosphorylates BAK1 and negatively regulates BAK1-mediated PTI responses such as MAPK3/4/6 activation, defence gene expression, reactive oxygen species bursts, stomatal immunity, callose deposition, and pathogen resistance. Although plant growth and 1000-seed weight of pp2c15 mutants were reduced compared to those of wild-type plants, pp2c5 mutants did not show any adverse effects. Thus, our findings strengthen the understanding of the mechanism by which PP2C family members negatively regulate plant immunity at multiple levels and indicate a possible approach to enhance plant resistance by eliminating specific PP2Cs without affecting plant growth and yield.

Genome-wide characterization of SOS1 gene family in potato (Solanum tuberosum) and expression analyses under salt and hormone stress

Salt Overly Sensitive 1 (SOS1) is one of the members of the Salt Overly Sensitive (SOS) signaling pathway and plays critical salt tolerance determinant in plants, while the characterization of the SOS1 family in potato (Solanum tuberosum) is lacking. In this study, 37 StSOS1s were identified and found to be unevenly distributed across 10 chromosomes, with most of them located on the plasma membrane. Promoter analysis revealed that the majority of these StSOS1 genes contain abundant cis-elements involved in various abiotic stress responses. Tissue specific expression showed that 21 of the 37 StSOS1s were widely expressed in various tissues or organs of the potato. Molecular interaction network analysis suggests that 25 StSOS1s may interact with other proteins involved in potassium ion transmembrane transport, response to salt stress, and cellular processes. In addition, collinearity analysis showed that 17, 8, 1 and 5 of orthologous StSOS1 genes were paired with those in tomato, pepper, tobacco, and Arabidopsis, respectively. Furthermore, RT-qPCR results revealed that the expression of StSOS1s were significant modulated by various abiotic stresses, in particular salt and abscisic acid stress. Furthermore, subcellular localization in Nicotiana benthamiana suggested that StSOS1-13 was located on the plasma membrane. These results extend the comprehensive overview of the StSOS1 gene family and set the stage for further analysis of the function of genes in SOS and hormone signaling pathways.

Genome-wide analysis and identification of TaRING-H2 gene family and TaSDIR1 positively regulates salt stress tolerance in wheat

Salt stress is an abiotic stress factor that limits high yields, and thus identifying salt tolerance genes is very important for improving the tolerance of salt in wheat. In this study we identified 274 TaRING-H2 family members and analyzed their gene positions, gene structures, conserved structural domains, promoter cis-acting elements and covariance relationships. And we investigated TaRING-H2-120 (TaSDIR1) in salt stress. Transgenic lines exhibited higher salt tolerance in the germination and seedling stages. Compared with the wild type, overexpression of TaSDIR1 upregulated the expression of genes encoding enzymes related to the control of reactive oxygen species (ROS), thereby reducing the accumulation of ROS, as well as increased the expression of ion transport-related genes to limit the inward flow of Na⁺ in vivo and maintain a higher K⁺/Na⁺ ratio. The expression levels of these genes were opposite in lines where TaSDIR1 was silenced by BSMV-VIGS, and the silenced wheat exhibited higher salt sensitivity. Arabidopsis mutants and heterologous TaSDIR1 overexpressing lines had similar salt stress tolerance phenotypes. We also demonstrated that TaSDIR1 interacted with TaSDIR1P2 in vivo and in vitro. A sequence of 80-100 amino acids in TaSDIR1P2 encoded a coiled coil domain that was important for the activity of E3 ubiquitin ligase, and it was also the core region for the interaction between TaSDIR1 and TaSDIR1P2. Overall, our results suggest that TaSDIR1 positively regulates salt stress tolerance in wheat.

Understandings and future challenges in soybean functional genomics and molecular breeding

Soybean (Glycine max) is a major source of plant protein and oil. Soybean breeding has benefited from advances in functional genomics. In particular, the release of soybean reference genomes has advanced our understanding of soybean adaptation to soil nutrient deficiencies, the molecular mechanism of symbiotic nitrogen (N) fixation, biotic and abiotic stress tolerance, and the roles of flowering time in regional adaptation, plant architecture, and seed yield and quality. Nevertheless, many challenges remain for soybean functional genomics and molecular breeding, mainly related to improving grain yield through high-density planting, maize-soybean intercropping, taking advantage of wild resources, utilization of heterosis, genomic prediction and selection breeding, and precise breeding through genome editing. This review summarizes the current progress in soybean functional genomics and directs future challenges for molecular breeding of soybean.

Unfolding molecular switches for salt stress resilience in soybean: recent advances and prospects for salt-tolerant smart plant production

The increasing sodium salts (NaCl, NaHCO3, NaSO4 etc.) in agricultural soil is a serious global concern for sustainable agricultural production and food security. Soybean is an important food crop, and their cultivation is severely challenged by high salt concentration in soils. Classical transgenic and innovative breeding technologies are immediately needed to engineer salt tolerant soybean plants. Additionally, unfolding the molecular switches and the key components of the soybean salt tolerance network are crucial for soybean salt tolerance improvement. Here we review our understandings of the core salt stress response mechanism in soybean. Recent findings described that salt stress sensing, signalling, ionic homeostasis (Na⁺/K⁺) and osmotic stress adjustment might be important in regulating the soybean salinity stress response. We also evaluated the importance of antiporters and transporters such as Arabidopsis K⁺ Transporter 1 (AKT1) potassium channel and the impact of epigenetic modification on soybean salt tolerance. We also review key phytohormones, and osmo-protectants and their role in salt tolerance in soybean. In addition, we discuss the progress of omics technologies for identifying salt stress responsive molecular switches and their targeted engineering for salt tolerance in soybean. This review summarizes recent progress in soybean salt stress functional genomics and way forward for molecular breeding for developing salt-tolerant soybean plant.