Oryza sativa, C4HC3-type really interesting new gene (RING), OsRFPv6, is a positive regulator in response to salt stress by regulating Na+ absorption

Rab7 GTPase-Mediated stress signaling enhances salinity tolerance in AlRabring7 tobacco transgenics by modulating physio-biochemical parameters

The RING-type E3 ligases play a significant role in stress signaling, primarily through post-translational regulation. Ubiquitination is a crucial post-translational modification that regulates the turnover and activity of proteins. The overexpression of AlRabring7, RING-HC E3 Ub ligase in tobacco provides insights into the regulation of salinity and ABA signaling in transgenic tobacco. The seed germination potential of AlRabring7 transgenics was higher than WT, with NaCl and ABA treatments. The transgenics showed improved morpho-physio-biochemical parameters in response to salinity and ABA treatments. The photosynthetic pigments, soluble sugars, reducing sugars and proline increased in transgenics in response to NaCl and ABA treatments. The decreased ROS accumulation in transgenics on NaCl and ABA treatments can be co-related to improved activity of enzymatic and non-enzymatic antioxidants. The potential of transgenics to maintain ABA levels with ABA treatment, highlights the active participation of ABA feedback loop mechanism. Interestingly, the ability of AlRabring7 transgenics to upregulate Rab7 protein, suggests its role in facilitating vacuolar transport. Furthermore, the improved potassium accumulation and reduced sodium content indicate an efficient ion regulation mechanism in transgenic plants facilitating higher stomatal opening. The expression of downstream ion transporter (NbNHX1 and NbVHA1), ABA signaling (NbABI2 and NbABI5) and vesicle trafficking (NbMON1) responsive genes were upregulated with stress. The present study, reports that AlRabring7 participates in maintaining vacuolar transport, ion balance, ROS homeostasis, stomatal regulation through activation of Rab7 protein and regulation of downstream stress-responsive during stress. This emphasizes the potential of AlRabring7 gene for improved performance and resilience in challenging environments.

Deciphering the mechanism of E3 ubiquitin ligases in plant responses to abiotic and biotic stresses and perspectives on PROTACs for crop resistance

With global climate change, it is essential to find strategies to make crops more resistant to different stresses and guarantee food security worldwide. E3 ubiquitin ligases are critical regulatory elements that are gaining importance due to their role in selecting proteins for degradation in the ubiquitin-proteasome proteolysis pathway. The role of E3 Ub ligases has been demonstrated in numerous cellular processes in plants responding to biotic and abiotic stresses. E3 Ub ligases are considered a class of proteins that are difficult to control by conventional inhibitors, as they lack a standard active site with pocket, and their biological activity is mainly due to protein-protein interactions with transient conformational changes. Proteolysis-targeted chimeras (PROTACs) are a new class of heterobifunctional molecules that have emerged in recent years as relevant alternatives for incurable human diseases like cancer because they can target recalcitrant proteins for destruction. PROTACs interact with the ubiquitin-proteasome system, principally the E3 Ub ligase in the cell, and facilitate proteasome turnover of the proteins of interest. PROTAC strategies harness the essential functions of E3 Ub ligases for proteasomal degradation of proteins involved in dysfunction. This review examines critical advances in E3 Ub ligase research in plant responses to biotic and abiotic stresses. It highlights how PROTACs can be applied to target proteins involved in plant stress response to mitigate pathogenic agents and environmental adversities.

The RING zinc finger protein LbRZF1 promotes salt gland development and salt tolerance in Limonium bicolor

The recretohalophyte Limonium bicolor thrives in high-salinity environments because salt glands on the above-ground parts of the plant help to expel excess salt. Here, we characterize a nucleus-localized C3HC4 (RING-HC)-type zinc finger protein of L. bicolor named  RING  ZINC  FINGER PROTEIN  1 (LbRZF1). LbRZF1 was expressed in salt glands and in response to NaCl treatment. LbRZF1 showed no E3 ubiquitin ligase activity. The phenotypes of overexpression and knockout lines for LbRZF1 indicated that LbRZF1 positively regulated salt gland development and salt tolerance in L. bicolor. lbrzf1 mutants had fewer salt glands and secreted less salt than did the wild-type, whereas LbRZF1-overexpressing lines had opposite phenotypes, in keeping with the overall salt tolerance of these plants. A yeast two-hybrid screen revealed that LbRZF1 interacted with LbCATALASE2 (LbCAT2) and the transcription factor LbMYB113, leading to their stabilization. Silencing of LbCAT2 or LbMYB113 decreased salt gland density and salt tolerance. The heterologous expression of LbRZF1 in Arabidopsis thaliana conferred salt tolerance to this non-halophyte. We also identified the transcription factor LbMYB48 as an upstream regulator of LbRZF1 transcription. The study of LbRZF1 in the regulation network of salt gland development also provides a good foundation for transforming crops and improving their salt resistance.

The B3 gene family in Medicago truncatula: Genome-wide identification and the response to salt stress

The B3 family genes constitute a pivotal group of transcription factors that assume diverse roles in the growth, development, and response to both biotic and abiotic stresses in plants. Medicago truncatula is a diploid plant with a relatively small genome, adopted as a model species for legumes genetics and functional genomic research. In this study, 173 B3 genes were identified in the M. truncatula genome, and classified into seven subgroups by phylogenetic analysis. Collinearity analysis revealed that 18 MtB3 gene pairs arose from segmented replication events. Analysis of expression patterns disclosed that 61 MtB3s exhibited a spectrum of expression profiles across various tissues and in the response to salt stress, indicating their potential involvement in salt stress signaling response. Among these genes, MtB3-53 exhibited tissue-specific differential expression and demonstrated a rapid response to salt stress induction. Overexpression of MtB3-53 gene in Arabidopsis improves salt stress tolerance by increasing plant biomass and chlorophyll content, while reducing leaf cell membrane damage. Moreover, salt treatment resulted in more up-regulation of AtABF1, AtABI3, AtHKT1, AtKIN1, AtNHX1, and AtRD29A in MtB3-53 transgenic Arabidopsis plants compared to the wild type, providing evidences that MtB3-53 enhances plant salt tolerance not only by modulating ion homeostasis but also by stimulating the production of antioxidants, which leads to the alleviation of cellular damage caused by salt stress. In conclusion, this study provides a fundamental basis for future investigations into the B3 gene family and its capacity to regulate plant responses to environmental stressors.

Overexpression of a C3HC4-type E3-ubiquitin ligase contributes to salinity tolerance by modulating Na+ homeostasis in rice

Soil salinity has a negative effect on crop yield. Therefore, plants have evolved many strategies to overcome decreases in yield under saline conditions. Among these, E3-ubiquitin ligase regulates salt tolerance. We characterized Oryza sativa Really Interesting New Gene (RING) Finger C3HC4-type E3 ligase (OsRFPHC-4), which plays a positive role in improving salt tolerance. The expression of OsRFPHC-4 was downregulated by high NaCl concentrations and induced by abscisic acid (ABA) treatment. GFP-fused OsRFPHC-4 was localized to the plasma membrane of rice protoplasts. OsRFPHC-4 encodes a cellular protein with a C3HC4-RING domain with E3 ligase activity. However, its variant OsRFPHC-4C161A does not possess this activity. OsRFPHC-4-overexpressing plants showed enhanced salt tolerance due to low accumulation of Na+ in both roots and leaves, low Na+ transport in the xylem sap, high accumulation of proline and soluble sugars, high activity of reactive oxygen species (ROS) scavenging enzymes, and differential regulation of Na+ /K+ transporter expression compared to wild-type (WT) and osrfphc-4 plants. In addition, OsRFPHC-4-overexpressing plants showed higher ABA sensitivity under exogenous ABA treatment than WT and osrfphc-4 plants. Overall, these results suggest that OsRFPHC-4 contributes to the improvement of salt tolerance and Na+ /K+ homeostasis via the regulation of changes in Na+ /K+ transporters.

How Plants Tolerate Salt Stress

Soil salinization inhibits plant growth and seriously restricts food security and agricultural development. Excessive salt can cause ionic stress, osmotic stress, and ultimately oxidative stress in plants. Plants exclude excess salt from their cells to help maintain ionic homeostasis and stimulate phytohormone signaling pathways, thereby balancing growth and stress tolerance to enhance their survival. Continuous innovations in scientific research techniques have allowed great strides in understanding how plants actively resist salt stress. Here, we briefly summarize recent achievements in elucidating ionic homeostasis, osmotic stress regulation, oxidative stress regulation, and plant hormonal responses under salt stress. Such achievements lay the foundation for a comprehensive understanding of plant salt-tolerance mechanisms.

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.

Identification and validation of two major QTLs for spikelet number per spike in wheat (Triticum aestivum L.)

The total number of spikelets (TSPN) and the number of fertile spikelets (FSPN) affect the final number of grains per spikelet in wheat. This study constructed a high-density genetic map using 55K single nucleotide polymorphism (SNP) arrays from a population of 152 recombinant inbred lines (RIL) from crossing the wheat accessions 10-A and B39. Twenty-four quantitative trait loci (QTLs) for TSPN and 18 QTLs for FSPN were localized based on the phenotype in 10 environments in 2019-2021. Two major QTLs, QTSPN/QFSPN.sicau-2D.4 (34.43-47.43 Mb) and QTSPN/QFSPN.sicau-2D.5(32.97-34.43 Mb), explained 13.97%-45.90% of phenotypic variation. Linked kompetitive allele-specific PCR (KASP) markers further validated these two QTLs and revealed that QTSPN.sicau-2D.4 had less effect on TSPN than QTSPN.sicau-2D.5 in 10-A×BE89 (134 RILs) and 10-A×Chuannong 16 (192 RILs) populations, and one population of Sichuan wheat (233 accessions). The alleles combination haplotype 3 with the allele from 10-A of QTSPN/QFSPN.sicau-2D.5 and the allele from B39 of QTSPN.sicau-2D.4 resulted in the highest number of spikelets. In contrast, the allele from B39 for both loci resulted in the lowest number of spikelets. Using bulk-segregant analysis-exon capture sequencing, six SNP hot spots that included 31 candidate genes were identified in the two QTLs. We identified Ppd-D1a from B39 and Ppd-D1d from 10-A and further analyzed Ppd-D1 variation in wheat. These results identified loci and molecular markers with potential utility for wheat breeding and laid a foundation for further fine mapping and cloning of the two loci.

RING Zinc Finger Proteins in Plant Abiotic Stress Tolerance

RING zinc finger proteins have a conserved RING domain, mainly function as E3 ubiquitin ligases, and play important roles in plant growth, development, and the responses to abiotic stresses such as drought, salt, temperature, reactive oxygen species, and harmful metals. RING zinc finger proteins act in abiotic stress responses mainly by modifying and degrading stress-related proteins. Here, we review the latest progress in research on RING zinc finger proteins, including their structural characteristics, classification, subcellular localization, and physiological functions, with an emphasis on abiotic stress tolerance. Under abiotic stress, RING zinc finger proteins on the plasma membrane may function as sensors or abscisic acid (ABA) receptors in abiotic stress signaling. Some RING zinc finger proteins accumulate in the nucleus may act like transcription factors to regulate the expression of downstream abiotic stress marker genes through direct or indirect ways. Most RING zinc finger proteins usually accumulate in the cytoplasm or nucleus and act as E3 ubiquitin ligases in the abiotic stress response through ABA, mitogen-activated protein kinase (MAPK), and ethylene signaling pathways. We also highlight areas where further research on RING zinc finger proteins in plants is needed.

RING E3 ubiquitin ligase TaSADR1 negatively regulates drought resistance in transgenic Arabidopsis

Drought stress is an important factor that affects crop yields and quality. E3 ubiquitin ligase has crucial roles in the responses to abiotic stresses. However, few studies have investigated the role of E3 ubiquitin ligase during drought stress in wheat. In this study, we cloned and identified the orthologous gene of Oryza sativa Salt-, ABA- and Drought-Induced RING Finger Protein 1 (OsSADR1) in wheat (Triticum aestivum L.) called TaSADR1. TaSADR1 encodes a protein containing 486 amino acids with a C3HC4 type RING finger conserved domain at the N-terminal. We confirmed that TaSADR1 has an E3 ubiquitin ligase activity and it is located in the nucleus. High expression of TaSADR1 was induced by treatment with PEG6000 and abscisic acid (ABA). TaSADR1-overexpressing transgenic Arabidopsis plants exhibited decreased drought tolerance. Under drought stress, compared with the wild-type (WT) lines, TaSADR1-overexpressing transgenic Arabidopsis lines had lower proline and chlorophyll contents, and antioxidant enzyme activities (superoxide dismutase, peroxidase, and catalase), whereas the water loss rate, malondialdehyde content, and relative electrolyte leakage were higher. In addition, the overexpressing transgenic Arabidopsis lines were more sensitive to mannitol and ABA treatment at seed germination and during seedling growth. The expression levels of genes related to stress were downregulated under drought conditions in the transgenic plants. Our results demonstrate that TaSADR1 may negatively regulate drought stress responses by regulating the expression of stress-related genes.

The Rice Abscisic Acid-Responsive RING Finger E3 Ligase OsRF1 Targets OsPP2C09 for Degradation and Confers Drought and Salinity Tolerance in Rice

Drought and salinity are major important factors that restrain growth and productivity of rice. In plants, many really interesting new gene (RING) finger proteins have been reported to enhance drought and salt tolerance. However, their mode of action and interacting substrates are largely unknown. Here, we identified a new small RING-H2 type E3 ligase OsRF1, which is involved in the ABA and stress responses of rice. OsRF1 transcripts were highly induced by ABA, salt, or drought treatment. Upregulation of OsRF1 in transgenic rice conferred drought and salt tolerance and increased endogenous ABA levels. Consistent with this, faster transcriptional activation of key ABA biosynthetic genes, ZEP, NCED3, and ABA4, was observed in OsRF1-OE plants compared with wild type in response to drought stress. Yeast two-hybrid assay, BiFC, and co-immunoprecipitation analysis identified clade A PP2C proteins as direct interacting partners with OsRF1. In vitro ubiquitination assay indicated that OsRF1 exhibited E3 ligase activity, and that it targeted OsPP2C09 protein for ubiquitination and degradation. Cell-free degradation assay further showed that the OsPP2C09 protein is more rapidly degraded by ABA in the OsRF1-OE rice than in the wild type. The combined results suggested that OsRF1 is a positive player of stress responses by modulating protein stability of clade A PP2C proteins, negative regulators of ABA signaling.