Plants involved in highly complex and well-coordinated systems have evolved a considerable degree of developmental plasticity, thus minimizing the damage caused by stress. MicroRNAs (miRNAs) have recently emerged as key regulators in gene regulation, developmental processes and stress tolerance in plants. In this study, soybean miRNAs associated with stress responses (drought, salinity, and alkalinity) have been identified and analyzed in combination with deep sequencing technology and in-depth bioinformatics analysis. One hundred and thirty three conserved miRNAs representing 95 miRNA families were expressed in soybeans under three treatments. In addition, 71, 50, and 45 miRNAs are either uniquely or differently expressed under drought, salinity, and alkalinity, respectively, suggesting that many miRNAs are inducible and are differentially expressed in response to certain stress. Our study has important implications for further identification of gene regulation under abiotic stresses and significantly contributes a complete profile of miRNAs in Glycine max.

Salinity is one of the most serious factors limiting the productivity of agricultural crops, with adverse effects on germination, plant vigor, and crop yield. This salinity may be natural or induced by agricultural activities such as irrigation or the use of certain types of fertilizer. The most detrimental effect of salinity stress is the accumulation of Na⁺ and Cl⁻ ions in tissues of plants exposed to soils with high NaCl concentrations. The entry of both Na⁺ and Cl⁻ into the cells causes severe ion imbalance, and excess uptake might cause significant physiological disorder(s). High Na⁺ concentration inhibits the uptake of K⁺, which is an element for plant growth and development that results in lower productivity and may even lead to death. The genetic analyses revealed K⁺ and Na⁺ transport systems such as SOS1, which belong to the CBL gene family and play a key role in the transport of Na⁺ from the roots to the aerial parts in the Arabidopsis plant. In this review, we mainly discuss the roles of alkaline cations K⁺ and Na⁺, Ion homeostasis-transport determinants, and their regulation. Moreover, we tried to give a synthetic overview of soil salinity, its effects on plants, and tolerance mechanisms to withstand stress.

Fifteen transcription factors in the CAMTA (calmodulin binding transcription activator) family of soybean were reported to differentially regulate in multiple stresses; however, their functional analyses had not yet been attempted. To characterize their role in stresses, we first comprehensively analyzed the GmCAMTA family in silico and thereafter determined their expression pattern under drought. The bioinformatics analysis revealed multiple stress-related cis-regulatory elements including ABRE, SARE, G-box and W-box, 10 unique miRNA (microRNA) targets in GmCAMTA transcripts and 48 proteins in GmCAMTAs’ interaction network. We then cloned the 2769 bp CDS (coding sequence) of GmCAMTA12 in an expression vector and overexpressed in soybean and Arabidopsis through Agrobacterium-mediated transformation. The T3 (Transgenic generation 3) stably transformed homozygous lines of Arabidopsis exhibited enhanced tolerance to drought in soil as well as on MS (Murashige and Skoog) media containing mannitol. In their drought assay, the average survival rate of transgenic Arabidopsis lines OE5 and OE12 (Overexpression Line 5 and Line 12) was 83.66% and 87.87%, respectively, which was ~30% higher than that of wild type. In addition, the germination and root length assays as well as physiological indexes such as proline and malondialdehyde contents, catalase activity and leakage of electrolytes affirmed the better performance of OE lines. Similarly, GmCAMTA12 overexpression in soybean promoted drought-efficient hairy roots in OE chimeric plants as compare to that of VC (Vector control). In parallel, the improved growth performance of OE in Hoagland-PEG (polyethylene glycol) and on MS-mannitol was revealed by their phenotypic, physiological and molecular measures. Furthermore, with the overexpression of GmCAMTA12, the downstream genes including AtAnnexin5, AtCaMHSP, At2G433110 and AtWRKY14 were upregulated in Arabidopsis. Likewise, in soybean hairy roots, GmELO, GmNAB and GmPLA1-IId were significantly upregulated as a result of GmCAMTA12 overexpression and majority of these upregulated genes in both plants possess CAMTA binding CGCG/CGTG motif in their promoters. Taken together, we report that GmCAMTA12 plays substantial role in tolerance of soybean against drought stress and could prove to be a novel candidate for engineering soybean and other plants against drought stress. Some research gaps were also identified for future studies to extend our comprehension of Ca-CaM-CAMTA-mediated stress regulatory mechanisms.

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.

Soil salinization is a widespread hindrance that endangers agricultural production and ecological security. High salt concentrations in saline soils are primarily caused by osmotic stress, ionic toxicity and oxidative stress, which have a negative impact on plant growth and development. In order to withstand salt stress, plants have developed a series of complicated physiological and molecular mechanisms, encompassing adaptive changes in the structure and function of various plant organs, as well as the intricate signal transduction networks enabling plants to survive in high-salinity environments. This review summarizes the recent advances in salt perception under different tissues, physiological responses and signaling regulations of plant tolerance to salt stress. We also examine the current knowledge of strategies for breeding salt-tolerant plants, including the applications of omics technologies and transgenic approaches, aiming to provide the basis for the cultivation of salt-tolerant crops through molecular breeding. Finally, future research on the application of wild germplasm resources and muti-omics technologies to discover new tolerant genes as well as investigation of crosstalk among plant hormone signaling pathways to uncover plant salt tolerance mechanisms are also discussed in this review.

Flavonoids are mainly associated with growth, development, and responses to diverse abiotic stresses in plants. A growing amount of data have demonstrated the biosynthesis of flavonoids through multienzyme complexes of which the membrane-bounded cytochrome P450 supergene family shares a crucial part. However, the explicit regulation mechanism of Cytochrome P450s related to flavonoid biosynthesis largely remains elusive. In the present study, we reported the identification of a stress-tolerant flavonoid biosynthetic CtCYP82G24 gene from Carthamus tinctorius. The transient transformation of CtCYP82G24 determined the subcellular localization to the cytosol. Heterologously expressed CtCYP82G24 was effective to catalyze the substrate-specific conversion, promoting the de novo biosynthesis of flavonoids in vitro. Furthermore, a qRT-PCR assay and the accumulation of metabolites demonstrated that the expression of CtCYP82G24 was effectively induced by Polyethylene glycol stress in transgenic Arabidopsis. In addition, the overexpression of CtCYP82G24 could also trigger expression levels of several other flavonoid biosynthetic genes in transgenic plants. Taken together, our findings suggest that CtCYP82G24 overexpression plays a decisive regulatory role in PEG-induced osmotic stress tolerance and alleviates flavonoid accumulation in transgenic Arabidopsis.