Overexpression of SmMYC2 enhances salt resistance in Arabidopsis thaliana and Salvia miltiorrhiza hairy roots

Functions of Basic Helix-Loop-Helix (bHLH) Proteins in the Regulation of Plant Responses to Cold, Drought, Salt, and Iron Deficiency: A Comprehensive Review

Abiotic stresses including cold, drought, salt, and iron deficiency severely impair plant development, crop productivity, and geographic distribution. Several bodies of research have shed light on the pleiotropic functions of BASIC HELIX-LOOP-HELIX (bHLH) proteins in plant responses to these abiotic stresses. In this review, we mention the regulatory roles of bHLH TFs in response to stresses such as cold, drought, salt resistance, and iron deficiency, as well as in enhancing grain yield in plants, especially crops. The bHLH proteins bind to E/G-box motifs in the target promoter and interact with various other factors to form a complex regulatory network. Through this network, they cooperatively activate or repress the transcription of downstream genes, thereby regulating various stress responses. Finally, we present some perspectives for future research focusing on the molecular mechanisms that integrate and coordinate these abiotic stresses. Understanding these molecular mechanisms is crucial for the development of stress-tolerant crops.

Genome-wide identification of ZmMYC2 binding sites and target genes in maize

BACKGROUND

Jasmonate (JA) is the important phytohormone to regulate plant growth and adaption to stress signals. MYC2, an bHLH transcription factor, is the master regulator of JA signaling. Although MYC2 in maize has been identified, its function remains to be clarified.

RESULTS

To understand the function and regulatory mechanism of MYC2 in maize, the joint analysis of DAP-seq and RNA-seq is conducted to identify the binding sites and target genes of ZmMYC2. A total of 3183 genes are detected both in DAP-seq and RNA-seq data, potentially as the directly regulating genes of ZmMYC2. These genes are involved in various biological processes including plant growth and stress response. Besides the classic cis-elements like the G-box and E-box that are bound by MYC2, some new motifs are also revealed to be recognized by ZmMYC2, such as nGCATGCAnn, AAAAAAAA, CACGTGCGTGCG. The binding sites of many ZmMYC2 regulating genes are identified by IGV-sRNA.

CONCLUSIONS

All together, abundant target genes of ZmMYC2 are characterized with their binding sites, providing the basis to construct the regulatory network of ZmMYC2 and better understanding for JA signaling in maize.

ZnO quantum dots alleviate salt stress in Salvia miltiorrhiza by enhancing growth, scavenging reactive oxygen species, and modulating stress-responsive genes

Experiments were conducted to investigate the alleviating effects of ZnO quantum dots (ZnO QDs) on salt stress in Salvia miltiorrhiza by comparing them with conventional ZnO nanoparticles (ZnO NPs). The results demonstrated that compared with salt stress alone, foliar application of ZnO QDs significantly improved the biomass as well as the total chlorophyll and carotenoids contents under salt stress. ZnO QDs reduced H2O2 and MDA levels, decreased non-enzymatic antioxidant (ASA and GSH) content, and improved antioxidant enzyme (POD, SOD, CAT, PAL, and PPO) activity under salt stress. Metal elemental analysis further demonstrated that the ZnO QDs markedly increased Zn and K contents while decreasing Na content, resulting in a lower Na/K ratio compared to salt stress alone. Finally, RNA sequencing results indicated that ZnO QDs primarily regulated genes associated with stress-responsive pathways, including plant hormone signal transduction, the MAPK signaling pathway, and metabolic-related pathways, thereby alleviating the adverse effects of salt stress. In comparison, ZnO NPs did not exhibit similar effects in terms of improving plant growth, enhancing the antioxidant system, or regulating stress-responsive genes under salt stress. These findings highlight the distinct advantages of ZnO QDs and suggest their potential as a valuable tool for mitigating salt stress in plants.

Transcriptome Analysis of Salvia miltiorrhiza under Drought Stress

Phenolic acids are one of the major secondary metabolites accumulated in Salvia miltiorrhiza with various pharmacological activities. Moderate drought stress can promote the accumulation of phenolic acids in S. miltiorrhiza, while the mechanism remains unclear. Therefore, we performed transcriptome sequencing of S. miltiorrhiza under drought treatment. A total of 47,169 unigenes were successfully annotated in at least one of the six major databases. Key enzyme genes involved in the phenolic acid biosynthetic pathway, including SmPAL, SmC4H, Sm4CL, SmTAT, SmHPPR, SmRAS and SmCYP98A14, were induced. Unigenes annotated as laccase correlated with SmRAS and SmCYP98A14 were analyzed, and seven candidates that may be involved in the key step of SalB biosynthesis by RA were obtained. A total of 15 transcription factors significantly up-regulated at 2 h and 4 h potentially regulating phenolic acid biosynthesis were screened out. TRINITY_DN14213_c0_g1 (AP2/ERF) significantly transactivated the expression of SmC4H and SmRAS, suggesting its role in the regulation of phenolic acid biosynthesis. GO and KEGG enrichment analysis of differential expression genes showed that phenylpropanoid biosynthesis and plant hormone signal transduction were significantly higher. The ABA-dependent pathway is essential for resistance to drought and phenolic acid accumulation. Expression patterns in drought and ABA databases showed that four PYLs respond to both drought and ABA, and three potential SnRK2 family members were annotated and analyzed. The present study presented a comprehensive transcriptome analysis of S. miltiorrhiza affected by drought, which provides a rich source for understanding the molecular mechanism facing abiotic stress in S. miltiorrhiza.

Heterologous expression of the Leymus chinensis metallothionein gene LcMT3 confers enhanced tolerance to salt stress in Escherichia coli, yeast, and Arabidopsis thaliana

Salinity is poisonous to various plant physiological processes and poses an increasingly severe threat to agricultural productivity worldwide. As a tactic to mitigate this issue, the hunt for salt-tolerance genes and pathways is intensifying. The low-molecular-weight proteins known as metallothioneins (MTs) can effectively reduce salt toxicity in plants. In seeking concrete evidence of its function under salt stress conditions, a unique salt-responsive metallothionein gene, LcMT3, was isolated from the extremely salt-enduring Leymus chinensis and heterologously characterized in Escherichia coli (E. coli), yeast (Saccharomyces cerevisiae), as well as Arabidopsis thaliana. Overexpression of LcMT3 imparted resistance to salt in E. coli cells and yeast, while the development of control cells was completely inhibited. Besides, transgenic plants expressing LcMT3 exhibited significantly enhanced salinity tolerance. They had higher germination rates and longer roots than their nontransgenic counterparts during NaCl tolerance. For several physiological indices of salt tolerance, transgenic lines reduced the accumulation of malondialdehyde (MDA), relative conductivity, and reactive oxygen species (ROS) in comparison to nontransgenic Arabidopsis. They also possessed increased concentrations of proline (Pro), relative water content, chlorophyll content, coupled with three more active antioxidant enzymes (superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT)). Transgenic plants also accumulated less Na+ and maintained a lower Na+/K+ ratio than control, which can be attributable to the transgene's regulatory effect on transporter proteins such as salt overly sensitive (SOS) and Na+/H+ antiporter (NHX1), as demonstrated by qPCR experiments. Collectively, LcMT3 could have a vital function in salinity resistance and be an essential candidate protein for abiotic stress.

Potential role of the regulatory miR1119-MYC2 module in wheat (Triticum aestivum L.) drought tolerance

MicroRNA (miRNA)-target gene modules are essential components of plants' abiotic stress signalling pathways Little is known about the drought-responsive miRNA-target modules in wheat, but systems biology approaches have enabled the prediction of these regulatory modules and systematic study of their roles in responses to abiotic stresses. Using such an approach, we sought miRNA-target module(s) that may be differentially expressed under drought and non-stressed conditions by mining Expressed Sequence Tag (EST) libraries of wheat roots and identified a strong candidate (miR1119-MYC2). We then assessed molecular and physiochemical differences between two wheat genotypes with contrasting drought tolerance in a controlled drought experiment and assessed possible relationships between their tolerance and evaluated traits. We found that the miR1119-MYC2 module significantly responds to drought stress in wheat roots. It is differentially expressed between the contrasting wheat genotypes and under drought versus non-stressed conditions. We also found significant associations between the module's expression profiles and ABA hormone content, water relations, photosynthetic activities, H₂O₂ levels, plasma membrane damage, and antioxidant enzyme activities in wheat. Collectively, our results suggest that a regulatory module consisting of miR1119 and MYC2 may play an important role in wheat's drought tolerance.

Genome-wide analysis of TPX2 gene family in Populus trichocarpa and its specific response genes under various abiotic stresses

Microtubules are essential for regulating cell morphogenesis, plant growth, and the response of plants to abiotic stresses. TPX2 proteins are the main players determining the spatiotemporally dynamic nature of the MTs. However, how TPX2 members respond to abiotic stresses in poplar remains largely unknown. Herein, 19 TPX2 family members were identified from the poplar genome and analyzed the structural characteristics as well as gene expression patterns. All TPX2 members had the conserved structural characteristics, but exhibited different expression profiles in different tissues, indicating their varying roles during plant growth. Additionally, several light, hormone, and abiotic stress responsive cis-acting regulatory elements were detected on the promoters of PtTPX2 genes. Furthermore, expression analysis in various tissues of Populus trichocarpa showed that the PtTPX2 genes responded differently to heat, drought and salt stress. In summary, these results provide a comprehensive analysis for the TPX2 gene family in poplar and an effective contribution to revealing the mechanisms of PtTPX2 in the regulatory network of abiotic stress.