AtPPRT3, a novel E3 ubiquitin ligase, plays a positive role in ABA signaling

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 Role of Plant Ubiquitin-like Modifiers in the Formation of Salt Stress Tolerance

The climate-driven challenges facing Earth necessitate a comprehensive understanding of the mechanisms facilitating plant resilience to environmental stressors. This review delves into the crucial role of ubiquitin-like modifiers, particularly focusing on ATG8-mediated autophagy, in bolstering plant tolerance to salt stress. Synthesising recent research, we unveil the multifaceted contributions of ATG8 to plant adaptation mechanisms amidst salt stress conditions, including stomatal regulation, photosynthetic efficiency, osmotic adjustment, and antioxidant defence. Furthermore, we elucidate the interconnectedness of autophagy with key phytohormone signalling pathways, advocating for further exploration into their molecular mechanisms. Our findings underscore the significance of understanding molecular mechanisms underlying ubiquitin-based protein degradation systems and autophagy in salt stress tolerance, offering valuable insights for designing innovative strategies to improve crop productivity and ensure global food security amidst increasing soil salinisation. By harnessing the potential of autophagy and other molecular mechanisms, we can foster sustainable agricultural practices and develop stress-tolerant crops resilient to salt stress.

Maize MITOGEN-ACTIVATED PROTEIN KINASE 20 mediates high-temperature-regulated stomatal movement

High temperature induces stomatal opening; however, uncontrolled stomatal opening is dangerous for plants in response to high temperature. We identified a high-temperature sensitive (hts) mutant from the ethyl methane sulfonate (EMS)-induced maize (Zea mays) mutant library that is linked to a single base change in MITOGEN-ACTIVATED PROTEIN KINASE 20 (ZmMPK20). Our data demonstrated that hts mutants exhibit substantially increased stomatal opening and water loss rate, as well as decreased thermotolerance, compared to wild-type plants under high temperature. ZmMPK20-knockout mutants showed similar phenotypes as hts mutants. Overexpression of ZmMPK20 decreased stomatal apertures, water loss rate, and enhanced plant thermotolerance. Additional experiments showed that ZmMPK20 interacts with MAP KINASE KINASE 9 (ZmMKK9) and E3 ubiquitin ligase RPM1 INTERACTING PROTEIN 2 (ZmRIN2), a maize homolog of Arabidopsis (Arabidopsis thaliana) RIN2. ZmMPK20 prevented ZmRIN2 degradation by inhibiting ZmRIN2 self-ubiquitination. ZmMKK9 phosphorylated ZmMPK20 and enhanced the inhibitory effect of ZmMPK20 on ZmRIN2 degradation. Moreover, we employed virus-induced gene silencing (VIGS) to silence ZmMKK9 and ZmRIN2 in maize and heterologously overexpressed ZmMKK9 or ZmRIN2 in Arabidopsis. Our findings demonstrated that ZmMKK9 and ZmRIN2 play negative regulatory roles in high-temperature-induced stomatal opening. Accordingly, we propose that the ZmMKK9-ZmMPK20-ZmRIN2 cascade negatively regulates high-temperature-induced stomatal opening and balances water loss and leaf temperature, thus enhancing plant thermotolerance.

Comparative physiological, antioxidant and proteomic investigation reveal robust response to cold stress in Digitalis purpurea L

BACKGROUND OF THE STUDY

Digitalis purpurea (L) is an important medicinal plant growing at Alpine region of Himalayas and withstands low temperatures and harsh climatic conditions existing at high altitude. It serves as an ideal plant system to decipher the tolerance to cold stress (CS) in plants from high altitudes.

METHODS AND RESULTS

To understand the complexity of plant response to CS, we performed a comparative physiological and biochemical study complemented with proteomics in one-month-old D. purpurea grown at 25 °C (control) and 4 °C (CS). We observed an enhanced accumulation of different osmo-protectants (glycine betaine, soluble sugar and proline) and higher transcription (mRNA levels) of various antioxidant enzymes with an increased antioxidant enzyme activity in D. purpurea when exposed to CS. Furthermore, higher concentrations of non-enzymatic antioxidants (flavonoids, phenolics) was also associated with the response to CS. Differential proteomic analysis revealed the role of various proteins primarily involved in redox reactions, protein stabilization, quinone and sterol metabolism involved in CS response in D. purpurea..

CONCLUSION

Our results provide a framework for better understanding the physiological and molecular mechanism of CS response in D. purpurea at high altitudes.

MbICE1 Confers Drought and Cold Tolerance through Up-Regulating Antioxidant Capacity and Stress-Resistant Genes in Arabidopsis thaliana

Malus baccata (L.) Borkh is an apple rootstock with good drought and cold resistance. The ICE gene is a key factor in the molecular mechanisms of plant drought and cold resistance. In the present research, the function of drought- and cold-induced MbICE1 of Malus baccata was investigated in Arabidopsis. According to GFP fluorescence images, MbICE1 was determined to be a nuclear protein. The MbICE1 was transferred to Arabidopsis, showing enhanced tolerance to drought and cold stresses. Under drought and cold treatments, the transgenic Arabidopsis had higher chlorophyll content and free proline content than WT plants, but the Malondialdehyde (MDA) content and electrolyte leakage (EL) were lower than those of WT plants. In addition, drought and cold led to a large accumulation of ROS (H₂O₂ and O^2-) content in Arabidopsis, while overexpression of MbICE1 enhanced the antioxidant enzyme activity in Arabidopsis and improved the plant's resistance to stresses. Moreover, the accumulation of MbICE1 promoted the expression of AtCBF1, AtCBF2, AtCBF3, AtCOR15a, AtCOR47 and AtKIN1 genes in Arabidopsis. These data indicate that MbICE1 is a key regulator of drought and cold and can be used as a backup gene for breeding Malus rootstocks.

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 Ubiquitin Switch in Plant Stress Response

Ubiquitin is a 76 amino acid polypeptide common to all eukaryotic organisms. It functions as a post-translationally modifying mark covalently linked to a large cohort of yet poorly defined protein substrates. The resulting ubiquitylated proteins can rapidly change their activities, cellular localization, or turnover through the 26S proteasome if they are no longer needed or are abnormal. Such a selective modification is essential to many signal transduction pathways particularly in those related to stress responses by rapidly enhancing or quenching output. Hence, this modification system, the so-called ubiquitin-26S proteasome system (UPS), has caught the attention in the plant research community over the last two decades for its roles in plant abiotic and biotic stress responses. Through direct or indirect mediation of plant hormones, the UPS selectively degrades key components in stress signaling to either negatively or positively regulate plant response to a given stimulus. As a result, a tightly regulated signaling network has become of much interest over the years. The ever-increasing changes of the global climate require both the development of new crops to cope with rapid changing environment and new knowledge to survey the dynamics of ecosystem. This review examines how the ubiquitin can switch and tune plant stress response and poses potential avenues to further explore this system.

AtPPRT1, an E3 Ubiquitin Ligase, Enhances the Thermotolerance in Arabidopsis

E3 ubiquitin ligase plays a vital role in the ubiquitin-mediated heat-related protein degradation pathway. Herein, we report that the expression of AtPPRT1, a C3HC4 zinc-finger ubiquitin E3 ligase gene, was induced by heat stress, and the β-glucuronidase (GUS) gene driven by the AtPPRT1 promoter has shown increased activity after basal and acquired thermotolerance. To further explore the function of AtPPRT1 in heat stress response (HSR), we used the atpprt1 mutant and AtPPRT1-overexpressing lines (OE2 and OE10) to expose in heat shock. In this study, the atpprt1 mutant had a lower germination and survival rate than those of Col-0 when suffered from the heat stress, whereas OEs enhanced basal and acquired thermotolerance in Arabidopsis seedlings. When compared to Col-0 and OEs, loss-of-function in AtPPRT1 resulted in lower chlorophyll retention and higher content of reactive oxygen species (ROS) after heat treatment. Moreover, the transcript levels of AtPPRT1 and several heat-related genes (AtZAT12, AtHSP21 and AtHSFA7a) were upregulated to greater extents in OEs and lower extents in atpprt1 compared to Col-0 after heat treated. Hence, we suggest that AtPPRT1 may act as a positive role in regulating the high temperature by mediating the degradation of unknown target proteins.