SUMO and SUMOylation in plants

Cytology, metabolomics, and proteomics reveal the grain filling process and quality difference of wheat

Comparative proteomics and non-target metabolomics, together with physiological and microstructural analyses of wheat grains (at 15, 20, 25, and 30 days after anthesis) from two different quality wheat varieties (Gaoyou 5766 (strong-gluten) and Zhoumai 18) were performed to illustrate the grain filling material dynamics and to search for quality control genes. The differential expressions of 1541 proteins and 406 metabolites were found. They were mostly engaged in protein metabolism, stress/defense, energy metabolism, and amino acid metabolism, and the metabolism of stored proteins and carbohydrates was the major focus of the latter stages. The core proteins and metabolites in the growth process were identified, and the candidate genes for quality differences were screened. In conclusion, this study offers a molecular explanation for the establishment of wheat quality, and it aids in our understanding of the intricate metabolic network between different qualities of wheat at the filling stage.

SIZ1-mediated SUMOylation of CPSF100 promotes plant thermomorphogenesis by controlling alternative polyadenylation

Under warm temperatures, plants adjust their morphologies for environmental adaption via precise gene expression regulation. However, the function and regulation of alternative polyadenylation (APA), an important fine-tuning of gene expression, remains unknown in plant thermomorphogenesis. In this study, we found that SUMOylation, a critical post-translational modification, is induced by a long-term treatment at warm temperatures via a SUMO ligase SIZ1 in Arabidopsis. Disruption of SIZ1 altered the global usage of polyadenylation signals and affected the APA dynamic of thermomorphogenesis-related genes. CPSF100, a key subunit of the CPSF complex for polyadenylation regulation, is SUMOylated by SIZ1. Importantly, we demonstrated that SUMOylation is essential for the function of CPSF100 in genome-wide polyadenylation site choice during thermomorphogenesis. Further analyses revealed that the SUMO conjugation on CPSF100 attenuates its interaction with two isoforms of its partner CPSF30, increasing the nuclear accumulation of CPSF100 for polyadenylation regulation. In summary, our study uncovers a regulatory mechanism of APA via SIZ1-mediated SUMOylation in plant thermomorphogenesis.

Targeted inhibition of SUMOylation: treatment of tumors

SUMOylation is a dynamic and reversible post-translational modification (PTM) of proteins involved in the regulation of biological processes such as protein homeostasis, DNA repair and cell cycle in normal and tumor cells. In particular, overexpression of SUMOylation components in tumor cells increases the activity of intracellular SUMOylation, protects target proteins against ubiquitination degradation and activation, promoting tumor cell proliferation and metastasis, providing immune evasion and increasing tolerance to chemotherapy and antitumor drugs. However, with the continuous research on SUMOylation and with the continued development of SUMOylation inhibitors, it has been found that tumor initiation and progression can be inhibited by blocking SUMOylation and/or in combination with drugs. SUMOylation is not a bad target when trying to treat tumor. This review introduces SUMOylation cycle pathway and summarizes the role of SUMOylation in tumor initiation and progression and SUMOylation inhibitors and their functions in tumors and provides a prospective view of SUMOylation as a new therapeutic target for tumors.

Insights into the role of SUMO in regulating drought stress responses in pigeonpea (Cajanus cajan)

KEY MESSAGE

We have identified and analyzed 28 SUMO-pathway proteins from pigeonpea. Enhanced transcripts of pathway genes and increased SUMO conjugation under drought signifies the role of SUMO in regulating stress. Being a protein-rich and nutrient-dense legume crop, pigeonpea (Cajanus cajan) holds a vital position in a vegetarian meal. It is a resilient crop capable of striving in harsh climates and provides a means of subsistence to small-holding farmers. Nevertheless, extremes of water scarcity and drought conditions, especially during seedling and reproductive stages, remains a major issue severely impacting the growth and overall productivity of pigeonpea. Small ubiquitin-like modifier (SUMO), a post-translational modification system, plays a pivotal role in fortifying plants against stressful conditions by rapid reprogramming of molecular events. In this study, we have scanned the entire pigeonpea genome and identified 28 candidates corresponding to SUMO machinery components of pigeonpea. qRT-PCR analysis of different SUMO machinery genes validated their presence under natural conditions. The analysis of the promoters of identified SUMO machinery genes revealed the presence of abiotic stress-related cis-regulatory elements highlighting the potential involvement of the genes in abiotic stress responses. The transcript level analysis of selected SUMO machinery genes and global SUMO status of pigeonpea proteins in response to drought stress suggests an integral role of SUMO in regulating drought stress conditions in pigeonpea. Collectively, the work puts forward a detailed in silico analysis of pigeonpea SUMO machinery candidates and highlights the essential role of SUMOylation in drought stress responses. Being the first report on a pulse crop, the study will serve as a resource for devising strategies for counteracting drought stress in pigeonpea that can be further extended to other pulse crops.

Small ubiquitin-like modifiers E3 ligases in plant stress

Plants regularly encounter various environmental stresses such as salt, drought, cold, heat, heavy metals and pathogens, leading to changes in their proteome. Of these, a post-translational modification, SUMOylation is particularly significant for its extensive involvement in regulating various plant molecular processes to counteract these external stressors. Small ubiquitin-like modifiers (SUMO) protein modification significantly contributes to various plant functions, encompassing growth, development and response to environmental stresses. The SUMO system has a limited number of ligases even in fully sequenced plant genomes but SUMO E3 ligases are pivotal in recognising substrates during the process of SUMOylation. E3 ligases play pivotal roles in numerous biological and developmental processes in plants, including DNA repair, photomorphogenesis, phytohormone signalling and responses to abiotic and biotic stress. A considerable number of targets for E3 ligases are proteins implicated in reactions to abiotic and biotic stressors. This review sheds light on how plants respond to environmental stresses by focusing on recent findings on the role of SUMO E3 ligases, contributing to a better understanding of how plants react at a molecular level to such stressors.

Gene pyramiding for boosted plant growth and broad abiotic stress tolerance

Abiotic stresses such as salinity, heat and drought seriously impair plant growth and development, causing a significant loss in crop yield and ornamental value. Biotechnology approaches manipulating specific genes prove to be effective strategies in crop trait modification. The Arabidopsis vacuolar pyrophosphatase gene AVP1, the rice SUMO E3 ligase gene OsSIZ1 and the cyanobacterium flavodoxin gene Fld have previously been implicated in regulating plant stress responses and conferring enhanced tolerance to different abiotic stresses when individually overexpressed in various plant species. We have explored the feasibility of combining multiple favourable traits brought by individual genes to acquire superior plant performance. To this end, we have simultaneously introduced AVP1, OsSIZ1 and Fld in creeping bentgrass. Transgenic (TG) plants overexpressing these three genes performed significantly better than wild type controls and the TGs expressing individual genes under both normal and various abiotic stress conditions, exhibited significantly enhanced plant growth and tolerance to drought, salinity and heat stresses as well as nitrogen and phosphate starvation, which were associated with altered physiological and biochemical characteristics and delicately fine-tuned expression of genes involved in plant stress responses. Our results suggest that AVP1, OsSIZ1 and Fld function synergistically to regulate plant development and plant stress response, leading to superior overall performance under both normal and adverse environments. The information obtained provides new insights into gene stacking as an effective approach for plant genetic engineering. A similar strategy can be extended for the use of other beneficial genes in various crop species for trait modifications, enhancing agricultural production.

NUA positively regulates plant immunity by coordination with ESD4 to deSUMOylate TPR1 in Arabidopsis

Nuclear pore complex (NPC) is composed of multiple nucleoporins (Nups). A plethora of studies have highlighted the significance of NPC in plant immunity. However, the specific roles of individual Nups are poorly understood. NUCLEAR PORE ANCHOR (NUA) is a component of NPC. Loss of NUA leads to an increase in SUMO conjugates and pleiotropic developmental defects in Arabidopsis thaliana. Herein, we revealed that NUA is required for plant defense against multiple pathogens. NUCLEAR PORE ANCHOR associates with the transcriptional corepressor TOPLESS-RELATED1 (TPR1) and contributes to TPR1 deSUMOylation. Significantly, NUA-interacting protein EARLY IN SHORT DAYS 4 (ESD4), a SUMO protease, specifically deSUMOylates TPR1. It has been previously established that the SUMO E3 ligase SAP AND MIZ1 DOMAIN-CONTAINING LIGASE 1 (SIZ1)-mediated SUMOylation of TPR1 represses the immune-related function of TPR1. Consistent with this notion, the hyper-SUMOylated TPR1 in nua-3 leads to upregulated expression of TPR1 target genes and compromised TPR1-mediated disease resistance. Taken together, our work uncovers a mechanism by which NUA positively regulates plant defense responses by coordination with ESD4 to deSUMOylate TPR1. Our findings, together with previous studies, reveal a regulatory module in which SIZ1 and NUA/ESD4 control the homeostasis of TPR1 SUMOylation to maintain proper immune output.

Post translational modifications at the verge of plant-geminivirus interaction

Plant-virus interaction is a complex phenomenon and involves the communication between plant and viral factors. Viruses have very limited coding ability yet, they are able to cause infection which results in huge agro-economic losses throughout the globe each year. Post-translational modifications (PTMs) are covalent modifications of proteins that have a drastic effect on their conformation, stability and function. Like the host proteins, geminiviral proteins are also subject to PTMs and these modifications greatly expand the diversity of their functions. Additionally, these viral proteins can also interact with the components of PTM pathways and modulate them. Several studies have highlighted the importance of PTMs such as phosphorylation, ubiquitination, SUMOylation, myristoylation, S-acylation, acetylation and methylation in plant-geminivirus interaction. PTMs also regulate epigenetic modifications during geminivirus infection which determines viral gene expression. In this review, we have summarized the role of PTMs in regulating geminiviral protein function, influence of PTMs on viral gene expression and how geminiviral proteins interact with the components of PTM pathways to modulate their function.

Gene co-expression network analysis for the selection of candidate early warning indicators of heat and nutrient stress in Posidonia oceanica

The continuous worldwide seagrasses decline calls for immediate actions in order to preserve this precious marine ecosystem. The main stressors that have been linked with decline in seagrasses are 1) the increasing ocean temperature due to climate change and 2) the continuous inputs of nutrients (eutrophication) associated with coastal human activities. To avoid the loss of seagrass populations, an "early warning" system is needed. We used Weighed Gene Co-expression Network Analysis (WGCNA), a systems biology approach, to identify potential candidate genes that can provide an early warning signal of stress in the Mediterranean iconic seagrass Posidonia oceanica, anticipating plant mortality. Plants were collected from both eutrophic (EU) and oligotrophic (OL) environments and were exposed to thermal and nutrient stress in a dedicated mesocosm. By correlating the whole-genome gene expression after 2-weeks exposure with the shoot survival percentage after 5-weeks exposure to stressors, we were able to identify several transcripts that indicated an early activation of several biological processes (BP) including: protein metabolic process, RNA metabolic process, organonitrogen compound biosynthetic process, catabolic process and response to stimulus, which were shared among OL and EU plants and among leaf and shoot apical meristem (SAM), in response to excessive heat and nutrients. Our results suggest a more dynamic and specific response of the SAM compared to the leaf, especially the SAM from plants coming from a stressful environment appeared more dynamic than the SAM from a pristine environment. A vast list of potential molecular markers is also provided that can be used as targets to assess field samples.

Rice SUMOs and unification of their names

Posttranslational modifications (PTMs) to proteins are regulatory mechanisms that play a critical role in regulating growth and development. The SUMO system is a rapid and dynamic PTM system employed by eukaryotic cells. Plant SUMOs are involved in many physiological processes, such as stress responses, regulation of flowering time and defense reactions to pathogen attack. In Arabidopsis thaliana and rice (Oryza sativa), eight and seven SUMO genes, respectively, were predicted by sequence analysis. Phylogenetic tree analysis of these SUMOs shows that they are divided into two groups. One consists of SUMOs that contain no SUMO acceptor site and are involved in monoSUMOylation of their target proteins. Rice OsSUMO1 and OsSUMO2 are in this group, and are structurally similar to each other and to Arabidopsis AtSUMO1. The other group is composed of SUMOs in which an acceptor site (ΨKXE/D) occurs inside the SUMO molecule, suggesting their involvement in polySUMOylation. Several studies on the rice SUMOs have been performed independently and reported. Individual names of rice SUMOs are confusing, because a unified nomenclature has not been proposed. This review clarifies the attribution of seven rice SUMOs and unifies the individual SUMO names.

Identification and functional characterization of the SUMO system in sweet potato under salt and drought stress

Sumoylation is a crucial post-translation modification (PTM) that is the covalent attachment of SUMO molecules to the substrate catalyzed by enzyme cascade. Sumoylation is essential in almost every physiological process of plants, particularly in response to abiotic stress. However, little is known about sumoylation in sweet potato (Ipomoea batatas), the world's seventh most important food crop. In this study, 17 sweet potato SUMO system genes have been cloned and functionally characterized. Multiple sequence alignment and phylogenetic analysis showed sweet potato SUMO system proteins had conserved domains and activity sites. IbSUMOs, IbSAE1, and IbSCE1 were localized in the cytoplasm and nucleus. E3 SUMO ligases showed nuclear or punctate localization. In vitro sumoylation assay confirmed the catalytic activity of sweet potato SUMO system components. Heterologous expression of IbSIZ1 genes in Arabidopsis atsiz1 mutant rescued the defective germination and growth phenotype. IbSCE1a/b and IbSIZ1a/b/c were salt and drought responsive genes. Heterologous expression of IbSCE1a/b/c improved the drought tolerance of Arabidopsis thaliana, while IbSIZ1a/b/c significantly enhanced the salt and drought tolerance. Our findings define that the SUMO system in sweet potato shared with conserved function but also possessed specific characterization. The resources presented here would facilitate uncovering the significance of sumoylation in sweet potato.

I Choose You: Selecting Accurate Reference Genes for qPCR Expression Analysis in Reproductive Tissues in Arabidopsis thaliana

Quantitative real-time polymerase chain reaction (qPCR) is a widely used method to analyse the gene expression pattern in the reproductive tissues along with detecting gene levels in mutant backgrounds. This technique requires stable reference genes to normalise the expression level of target genes. Nonetheless, a considerable number of publications continue to present qPCR results normalised to a single reference gene and, to our knowledge, no comparative evaluation of multiple reference genes has been carried out in specific reproductive tissues of Arabidopsis thaliana. Herein, we assessed the expression stability levels of ten candidate reference genes (UBC9, ACT7, GAPC-2, RCE1, PP2AA3, TUA2, SAC52, YLS8, SAMDC and HIS3.3) in two conditional sets: one across flower development and the other using inflorescences from different genotypes. The stability analysis was performed using the RefFinder tool, which combines four statistical algorithms (geNorm, NormFinder, BestKeeper and the comparative ΔCt method). Our results showed that RCE1, SAC52 and TUA2 had the most stable expression in different flower developmental stages while YLS8, HIS3.3 and ACT7 were the top-ranking reference genes for normalisation in mutant studies. Furthermore, we validated our results by analysing the expression pattern of genes involved in reproduction and examining the expression of these genes in published mutant backgrounds. Overall, we provided a pool of appropriate reference genes for expression studies in reproductive tissues of A. thaliana, which will facilitate further gene expression studies in this context. More importantly, we presented a framework that will promote a consistent and accurate analysis of gene expression in any scientific field. Simultaneously, we highlighted the relevance of clearly defining and describing the experimental conditions associated with qPCR to improve scientific reproducibility.

Plant deubiquitinases: from structure and activity to biological functions

This article attempts to provide comprehensive review of plant deubiquitinases, paying special attention to recent advances in their biochemical activities and biological functions. Proteins in eukaryotes are subjected to post-translational modifications, in which ubiquitination is regarded as a reversible process. Cellular deubiquitinases (DUBs) are a key component of the ubiquitin (Ub)-proteasome system responsible for cellular protein homeostasis. DUBs recycle Ub by hydrolyzing poly-Ub chains on target proteins, and maintain a balance of the cellular Ub pool. In addition, some DUBs prefer to cleave poly-Ub chains not linked through the conventional K48 residue, which often alter the substrate activity instead of its stability. In plants, all seven known DUB subfamilies have been identified, namely Ub-binding protease/Ub-specific protease (UBP/USP), Ub C-terminal hydrolase (UCH), Machado-Joseph domain-containing protease (MJD), ovarian-tumor domain-containing protease (OTU), zinc finger with UFM1-specific peptidase domain protease (ZUFSP), motif interacting with Ub-containing novel DUB family (MINDY), and JAB1/MPN/MOV34 protease (JAMM). This review focuses on recent advances in the structure, activity, and biological functions of plant DUBs, particularly in the model plant Arabidopsis.

The SUMOylation Pathway Components Are Required for Vegetative Growth, Asexual Development, Cytotoxic Responses, and Programmed Cell Death Events in Fusarium oxysporum f. sp. niveum

SUMOylation is an essential protein modification process that regulates numerous crucial cellular and biochemical processes in phytopathogenic fungi, and thus plays important roles in multiple biological functions. The present study characterizes the SUMOylation pathway components, including SMT3 (SUMO), AOS1 (an E1 enzyme), UBC9 (an E2 enzyme), and MMS21 (an E3 ligase), in Fusarium oxysporum f. sp. niveum (Fon), the causative agent of watermelon Fusarium wilt, in terms of the phylogenetic relationship, gene/protein structures, and basic biological functions. The SUMOylation components FonSMT3, FonAOS1, FonUBC9, and FonMMS21 are predominantly located in the nucleus. FonSMT3, FonAOS1, FonUBC9, and FonMMS21 are highly expressed in the germinating macroconidia, but their expression is downregulated gradually in infected watermelon roots with the disease progression. The disruption of FonUBA2 and FonSIZ1 seems to be lethal in Fon. The deletion mutant strains for FonSMT3, FonAOS1, FonUBC9, and FonMMS21 are viable, but exhibit significant defects in vegetative growth, asexual reproduction, conidial morphology, spore germination, responses to metal ions and DNA-damaging agents, and apoptosis. The disruption of FonSMT3, FonAOS1, FonUBC9, and FonMMS21 enhances sensitivity to cell wall-perturbing agents, but confers tolerance to digestion by cell wall-degrading enzymes. Furthermore, the disruption of FonSMT3, FonAOS1, and FonUBC9 negatively regulates autophagy in Fon. Overall, these results demonstrate that the SUMOylation pathway plays vital roles in regulating multiple basic biological processes in Fon, and, thus, can serve as a potential target for developing a disease management approach to control Fusarium wilt in watermelon.

Optimising expression and extraction of recombinant proteins in plants

Recombinant proteins are of paramount importance for research, industrial and medical use. Numerous expression chassis are available for recombinant protein production, and while bacterial and mammalian cell cultures are the most widely used, recent developments have positioned transgenic plant chassis as viable and often preferential options. Plant chassis are easily maintained at low cost, are hugely scalable, and capable of producing large quantities of protein bearing complex post-translational modification. Several protein targets, including antibodies and vaccines against human disease, have been successfully produced in plants, highlighting the significant potential of plant chassis. The aim of this review is to act as a guide to producing recombinant protein in plants, discussing recent progress in the field and summarising the factors that must be considered when utilising plants as recombinant protein expression systems, with a focus on optimising recombinant protein expression at the genetic level, and the subsequent extraction and purification of target proteins, which can lead to substantial improvements in protein stability, yield and purity.

NUA and ESD4 negatively regulate ABA signaling during seed germination

The phytohormone abscisic acid (ABA) plays important roles in plant growth, development and adaptative responses to abiotic stresses. SNF1-related protein kinase 2s (SnRK2) are key components that activate the ABA core signaling pathway. NUCLEAR PORE ANCHOR (NUA) is a component of the nuclear pore complex (NPC) that involves in deSUMOylation through physically interacting with the EARLY IN SHORT DAYS 4 (ESD4) SUMO protease. However, it is not clear how NUA functions with SnRK2 and ESD4 to regulate ABA signaling. In our study, we found that nua loss-of-function mutants exhibited pleiotropic ABA-hypersensitive phenotype. We also found that ABA-responsive genes remarkably up-regulated in nua by exogenous ABA. The nua snrk2.2 snrk2.3 triple mutant and nua abi5 double mutant partially rescued the ABA-hypersensitive phenotype of nua, thereby suggesting that NUA is epistatic to SnRK2s. Additionally, we observed that esd4-3 mutant was also ABA-hypersensitive. NUA and ESD4 were further demonstrated to physically interact with SnRK2s and negatively regulate ABA signaling by reducing SnRK2s stability. Taken together, our findings uncover a new regulatory mechanism that can modulate ABA signaling.

Understanding SUMO-mediated adaptive responses in plants to improve crop productivity

The response to abiotic and biotic stresses in plants and crops is considered a multifaceted process. Due to their sessile nature, plants have evolved unique mechanisms to ensure that developmental plasticity remains during their life cycle. Among these mechanisms, post-translational modifications (PTMs) are crucial components of adaptive responses in plants and transduce environmental stimuli into cellular signalling through the modulation of proteins. SUMOylation is an emerging PTM that has received recent attention due to its dynamic role in protein modification and has quickly been considered a significant component of adaptive mechanisms in plants during stress with great potential for agricultural improvement programs. In the present review, we outline the concept that small ubiquitin-like modifier (SUMO)-mediated response in plants and crops to abiotic and biotic stresses is a multifaceted process with each component of the SUMO cycle facilitating tolerance to several different environmental stresses. We also highlight the clear increase in SUMO genes in crops when compared with Arabidopsis thaliana. The SUMO system is understudied in crops, given the importance of SUMO for stress responses, and for some SUMO genes, the apparent expansion provides new avenues to discover SUMO-conjugated targets that could regulate beneficial agronomical traits.

The transcription factor MdMYB2 influences cold tolerance and anthocyanin accumulation by activating SUMO E3 ligase MdSIZ1 in apple

Conjugation of the small ubiquitin-like modifier (SUMO) peptide to target proteins is an important post-translational modification. SAP AND MIZ1 DOMAIN-CONTAINING LIGASE1 (MdSIZ1) is an apple (Malus domestica Borkh). SUMO E3 ligase that mediates sumoylation of its targets during plant growth and development under adverse environmental conditions. However, it is unclear how MdSIZ1 senses the various environmental signals and whether sumoylation is regulated at the transcriptional level. In this study, we analyzed the MdSIZ1 promoter and found that it contained an MYB binding site (MBS) motif that was essential for the response of MdSIZ1 to low temperature (LT) and drought. Subsequently, we used yeast one-hybridization screening to demonstrate that a MYB transcription factor, MdMYB2, directly bound to the MBS motif in the MdSIZ1 promoter. Phenotypic characterization of MdMYB2 and MdSIZ1 suggested that the expression of both MdMYB2 and MdSIZ1 substantially improved cold tolerance in plants. MdMYB2 was induced by LT and further activated the expression of MdSIZ1, thereby promoting the sumoylation of MdMYB1, a key regulator of anthocyanin biosynthesis in apple. MdMYB2 promoted anthocyanin accumulation in apple fruits, apple calli, and Arabidopsis (Arabidopsis thaliana) in an MdSIZ1-dependent manner. In addition, the interaction of MdMYB2 and the MdSIZ1 promoter substantially improved plant tolerance to cold stress. Taken together, our findings reveal an important role for transcriptional regulation of sumoylation and provide insights into plant anthocyanin biosynthesis regulation mechanisms and stress response.

Involvement of dehydrin proteins in mitigating the negative effects of drought stress in plants

Drought stress-induced crop loss has been considerably increased in recent years because of global warming and changing rainfall pattern. Natural drought-tolerant plants entail the recruitment of a variety of metabolites and low molecular weight proteins to negate the detrimental effects of drought stress. Dehydrin (DHN) proteins are one such class of proteins that accumulate in plants during drought and associated stress conditions. These proteins are highly hydrophilic and perform multifaceted roles in the protection of plant cells during drought stress conditions. Evidence gathered over the years suggests that DHN proteins impart drought stress tolerance by enhancing the water retention capacity, elevating chlorophyll content, maintaining photosynthetic machinery, activating ROS detoxification, and promoting the accumulation of compatible solutes, among others. Overexpression studies have indicated that these proteins can be effectively targeted to mitigate the negative effects of drought stress and for the development of drought stress-tolerant crops to feed the ever-growing population in the near future. In this review, we describe the mechanism of DHNs mediated drought stress tolerance in plants and their interaction with several phytohormones to provide an in-depth understanding of DHNs function.

Epigenetic modifications from arsenic exposure: A comprehensive review

Arsenic is a notorious element with the potential to harm exposed individuals in ways that include cancerous and non-cancerous health complications. Millions of people across the globe (especially in South and Southeast Asian countries including China, Vietnam, India and Bangladesh) are currently being unknowingly exposed to precarious levels of arsenic. Among the diverse effects associated with such arsenic levels of exposure is the propensity to alter the epigenome. Although a large volume of literature exists on arsenic-induced genotoxicity, cytotoxicity, and inter-individual susceptibility due to active research on these subject areas from the last millennial, it is only recently that attention has turned on the ramifications and mechanisms of arsenic-induced epigenetic changes. The present review summarizes the possible mechanisms involved in arsenic induced epigenetic alterations. It focuses on the mechanisms underlying epigenome reprogramming from arsenic exposure that result in improper cell signaling and dysfunction of various epigenetic components. The mechanistic information articulated from the review is used to propose a number of novel therapeutic strategies with a potential for ameliorating the burden of worldwide arsenic poisoning.

Capsicum SIZ1 contributes to ABA-induced SUMOylation in pepper

Abiotic and biotic stresses are the major factors limiting plant growth. Arabidopsis E3 SUMO ligase SIZ1 plays an essential role in plant stress tolerance. Herein, we identified a SIZ/PAIS-type protein in pepper (Capsicum annuum), namely CaSIZ1, which shares 60 % sequence identity with AtSIZ1. The stems and flowers of pepper had a relatively higher expression of CaSIZ1 than the fruits, leaves, and roots. ABA and NaCl treatments induced CaSIZ1. CaSIZ1 protein was localized in the nucleus and partially rescued the dwarf and ABA-sensitive phenotypes of Atsiz1-2, suggesting the functional replacement of CaSIZ1 with AtSIZ1. We found that CaSIZ1 interacted with CaABI5, and ABA promoted the accumulation of SUMO conjugates in pepper. CaSIZ1 knockdown did not only reduce ABA-induced SUMOylation, but also attenuated the salt tolerance of pepper. Overall, the results of this study suggest that CaSIZ1 has a significant role in ABA-induced SUMOylation and stress response.

Molecular Characterization and Functional Localization of a Novel SUMOylation Gene in Oryza sativa

Simple Summary

The small ubiquitin-related modifier genes regulate the function of the cellular proteins, which are associated with cell stress-tolerance. Identification and understanding the functional localization of these genes are very important to mitigate the stresses. In this study, we identified a novel small ubiquitin-related modifier gene and studied its functional localization in the cell. This new finding will be very valuable in increasing our understanding of the mechanism of stress-tolerance.

Abstract

Small ubiquitin-related modifier (SUMO) regulates the cellular function of diverse proteins through post-translational modifications. The current study defined a new homolog of SUMO genes in the rice genome and named it OsSUMO7. Putative protein analysis of OsSUMO7 detected SUMOylation features, including di-glycine (GG) and consensus motifs (ΨKXE/D) for the SUMOylation site. Phylogenetic analysis demonstrated the high homology of OsSUMO7 with identified rice SUMO genes, which indicates that the OsSUMO7 gene is an evolutionarily conserved SUMO member. RT-PCR analysis revealed that OsSUMO7 was constitutively expressed in all plant organs. Bioinformatic analysis defined the physicochemical properties and structural model prediction of OsSUMO7 proteins. A red fluorescent protein (DsRed), fused with the OsSUMO7 protein, was expressed and localized mainly in the nucleus and formed nuclear subdomain structures. The fusion proteins of SUMO-conjugating enzymes with the OsSUMO7 protein were co-expressed and co-localized in the nucleus and formed nuclear subdomains. This indicated that the OsSUMO7 precursor is processed, activated, and transported to the nucleus through the SUMOylation system of the plant cell.

SUMO Modification of OsFKBP20-1b Is Integral to Proper Pre-mRNA Splicing upon Heat Stress in Rice

OsFKBP20-1b, a plant-specific cyclophilin protein, has been implicated to regulate pre-mRNA splicing under stress conditions in rice. Here, we demonstrated that OsFKBP20-1b is SUMOylated in a reconstituted SUMOylation system in E.coli and in planta, and that the SUMOylation-coupled regulation was associated with enhanced protein stability using a less SUMOylated OsFKBP20-1b mutant (5KR_OsFKBP20-1b). Furthermore, OsFKBP20-1b directly interacted with OsSUMO1 and OsSUMO2 in the nucleus and cytoplasm, whereas the less SUMOylated 5KR_OsFKBP20-1b mutant had an impaired interaction with OsSUMO1 and 2 in the cytoplasm but not in the nucleus. Under heat stress, the abundance of an OsFKBP20-1b-GFP fusion protein was substantially increased in the nuclear speckles and cytoplasmic foci, whereas the heat-responsiveness was remarkably diminished in the presence of the less SUMOylated 5KR_OsFKBP20-1b-GFP mutant. The accumulation of endogenous SUMOylated OsFKBP20-1b was enhanced by heat stress in planta. Moreover, 5KR_OsFKBP20-1b was not sufficiently associated with the U snRNAs in the nucleus as a spliceosome component. A protoplast transfection assay indicated that the low SUMOylation level of 5KR_OsFKBP20-1b led to inaccurate alternative splicing and transcription under heat stress. Thus, our results suggest that OsFKBP20-1b is post-translationally regulated by SUMOylation, and the modification is crucial for proper RNA processing in response to heat stress in rice.

Increasing temperature elevates the variation and spatial differentiation of pesticide tolerance in a plant pathogen

Climate change and pesticide resistance are two of the most imminent challenges human society is facing today. Knowledge of how the evolution of pesticide resistance may be affected by climate change such as increasing air temperature on the planet is important for agricultural production and ecological sustainability in the future but is lack in scientific literatures reported from empirical research. Here, we used the azoxystrobin-Phytophthora infestans interaction in agricultural systems to investigate the contributions of environmental temperature to the evolution of pesticide resistance and infer the impacts of global warming on pesticide efficacy and future agricultural production and ecological sustainability. We achieved this by comparing azoxystrobin sensitivity of 180 P. infestans isolates sampled from nine geographic locations in China under five temperature schemes ranging from 13 to 25°C. We found that local air temperature contributed greatly to the difference of azoxystrobin tolerance among geographic populations of the pathogen. Both among-population and within-population variations in azoxystrobin tolerance increased as experimental temperatures increased. We also found that isolates with higher azoxystrobin tolerance adapted to a broader thermal niche. These results suggest that global warming may enhance the risk of developing pesticide resistance in plant pathogens and highlight the increased challenges of administering pesticides for effective management of plant diseases to support agricultural production and ecological sustainability under future thermal conditions.

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.

Plant SUMO E3 Ligases: Function, Structural Organization, and Connection With DNA

Protein modification by the small ubiquitin-like modifier (SUMO) plays an important role in multiple plant processes, including growth, development, and the response to abiotic stresses. Mechanistically, SUMOylation is a sequential multi-enzymatic process where SUMO E3 ligases accelerate SUMO conjugation while also influencing target identity and interactions. This review explores the biological functions of plant SUMO E3 ligases [SAP AND MIZ1 DOMAIN-CONTAINING LIGASE (SIZs), METHYL METHANESULFONATE-SENSITIVITY PROTEIN 21 (MMS21s), and PROTEIN INHIBITOR OF ACTIVATED STAT-LIKE (PIALs)] in relation to their molecular activities and domains. We also explore the sub-cellular localization of SUMO E3 ligases and review evidence suggesting a connection between certain SUMO E3 ligases and DNA that contributes to gene expression regulation.

Towards understanding the multifaceted role of SUMOylation in plant growth and development

Post-translational modifications (PTMs) play a critical role in regulating plant growth and development through the modulation of protein functionality and its interaction with its partners. Analysis of the functional implication of PTMs on plant cellular signalling presents grand challenges in understanding their significance. Proteins decorated or modified with another chemical group or polypeptide play a significant role in regulating physiological processes as compared with non-decorated or non-modified proteins. In the past decade, SUMOylation has been emerging as a potent PTM influencing the adaptability of plants to growth, in response to various environmental cues. Deciphering the SUMO-mediated regulation of plant stress responses and its consequences is required to understand the mechanism underneath. Here, we will discuss the recent advances in the role and significance of SUMOylation in plant growth, development and stress response.

Functional characterization of VviDHN2 and VviDHN4 dehydrin isoforms from Vitis vinifera (L.): An in silico and in vitro approach

Dehydrins, a family of hydrophilic and intrinsically disordered proteins, are a subgroup of late embryogenesis abundant proteins that perform different protective roles in plants. Although the transition from a disordered to an ordered state has been associated with dehydrin function or interactions with specific partner molecules, the question of how the primary and secondary dehydrin protein structure is related to specific functions or target molecule preferences remains unresolved. This work addresses the in silico sequencing analysis and in vitro functional characterization of two dehydrin isoforms, VviDHN2 and VviDHN4, from Vitis vinifera. Conformational changes suggest potential interactions with a broad range of molecules and could point to more than one function. The in silico analysis showed differences in conserved segments, specific amino acid binding sequences, heterogeneity of structural properties and predicted sites accessible for various post-translational modifications between the sequence of both dehydrins. Moreover, in vitro functional analysis revealed that although they both showed slight antifungal activity, only VviDHN4 acts as a molecular shield that protects proteins from freezing and dehydration. VviDHN4 also demonstrated high potential as a chaperone and reactive oxygen species scavenger, in addition to presenting antifreeze activity, all of which confirms its multifunctional nature. Our findings highlight the significant role of Y-segments and the differential and specific amino acid composition of less conserved segments that are rich in polar/charged residues between S- and K-segments, coupled with post-translational modifications, in modulating and switching dehydrin biological function.

Epigenetic regulation of geminivirus pathogenesis: a case of relentless recalibration of defence responses in plants

Geminiviruses constitute one of the largest families of plant viruses and they infect many economically important crops. The proteins encoded by the single-stranded DNA genome of these viruses interact with a wide range of host proteins to cause global dysregulation of cellular processes and help establish infection in the host. Geminiviruses have evolved numerous mechanisms to exploit host epigenetic processes to ensure the replication and survival of the viral genome. Here, we review our current knowledge of diverse epigenetic processes that have been implicated in the regulation of geminivirus pathogenesis, including DNA methylation, histone post-transcriptional modification, chromatin remodelling, and nucleosome repositioning. In addition, we discuss the currently limited evidence of host epigenetic defence responses that are aimed at counteracting geminivirus infection, and the potential for exploiting these responses for the generation of resistance against geminiviruses in crop species.

Proteomic analysis of SUMO1-SUMOylome changes during defense elicitation in Arabidopsis

Rapid adaptation of plants to developmental or physiological cues is facilitated by specific receptors that transduce the signals mostly via post-translational modification (PTM) cascades of downstream partners. Reversible covalent attachment of SMALL UBIQUITIN-LIKE MODIFIER (SUMO), a process termed as SUMOylation, influence growth, development and adaptation of plants to various stresses. Strong regulatory mechanisms maintain the steady-state SUMOylome and mutants with SUMOylation disturbances display mis-primed immunity often with growth consequences. Identity of the SUMO-substrates undergoing SUMOylation changes during defenses however remain largely unknown. Here we exploit either the auto-immune property of an Arabidopsis mutant or defense responses induced in wild-type plants against Pseudomonas syringae pv tomato (PstDC3000) to enrich and identify SUMO1-substrates. Our results demonstrate massive enhancement of SUMO1-conjugates due to increased SUMOylation efficiencies during defense responses. Of the 261 proteins we identify, 29 have been previously implicated in immune-associated processes. Role of others expand to diverse cellular roles indicating massive readjustments the SUMOylome alterations may cause during induction of immunity. Overall, our study highlights the complexities of a plant immune network and identifies multiple SUMO-substrates that may orchestrate the signaling. SIGNIFICANCE: In all eukaryotes, covalent linkage of the SMALL UBIQUITIN-LIKE MODIFIER (SUMOs), a process termed as SUMOylation, on target proteins affect their fate and function. Plants display reversible readjustments in the pool of SUMOylated proteins during biotic and abiotic stress responses. Here, we demonstrate net increase in global SUMO1/2-SUMOylome of Arabidopsis thaliana at induction of immunity. We enrich and identify 261 SUMO1-substrates enhanced in defenses that categorize to diverse cellular processes and include novel candidates with uncharacterized immune-associated roles. Overall, our results highlight intricacies of SUMO1-orchestration in defense signaling networks.

Transcriptome profiling and weighted gene co-expression network analysis of early floral development in Aquilegia coerulea

The earliest phases of floral development include a number of crucial processes that lay the foundation for the subsequent morphogenesis of floral organs and success in reproduction. Currently, key transcriptional changes during this developmental window have been characterized in the model species Arabidopsis thaliana, but little is known about how transcriptional dynamics change over the course of these developmental processes in other plant systems. Here, we have conducted the first in-depth transcriptome profiling of early floral development in Aquilegia at four finely dissected developmental stages, with eight biological replicates per stage. Using differential gene expression analysis and weighted gene co-expression network analysis, we identified both crucial genes whose expression changes mark the transitions between developmental stages and hub genes in co-expression modules. Our results support the potential functional conservation of key genes in early floral development that have been identified in other systems, but also reveal a number of previously unknown or overlooked loci that are worthy of further investigation. In addition, our results highlight not only the dynamics of transcriptional regulation during early floral development, but also the potential involvement of the complex, essential networks of small RNA and post-translational regulation to these developmental stages.

SUMOylation in fungi: A potential target for intervention

SUMOylation is a post-translational, reversible modification process which occurs in eukaryotes. Small Ubiquitin like MOdifier or (SUMO) proteins are a family of small proteins that are covalently attached to and detached from other proteins to modify the target protein function. In pathogenic fungi, SUMO has been identified and preliminary studies indicate its importance either for survival and/or for virulence. In this review we provide an overview of the current state of knowledge of SUMOylation in fungi and the effects on pathogenesis. Subsequently we identify the orthologs of the SUMOylation pathway components across fungi. We also show the level of conservation of the proteins involved and identify the similarities/differences in the orthologs across fungi and the human and plant hosts to identify potential targets of intervention.

Stability of Begomoviral pathogenicity determinant βC1 is modulated by mutually antagonistic SUMOylation and SIM interactions

BACKGROUND

To successfully invade new hosts, plant viruses must break host resistance and be competent to move within and between plant cells. As a means, viral proteins known as pathogenicity determinants have evolved to coordinate a network of protein interactions. The βC1 protein encoded by specific geminiviral satellites acts as a key pathogenicity determinant for this disease-causing family of plant viruses. Post-translational modifications (PTMs) such as ubiquitination and phosphorylation of the βC1 protein have been shown to occur in diverse viruses. However, the relevance of these and other layers of PTMs in host-geminiviral interactions has not been fully understood.

RESULTS

Here we identified the significance of a novel layer of PTMs in the βC1 protein of Synedrella yellow vein clearing virus (SyYVCV), a newly identified member of the Begomovirus genus of Geminiviruses. This protein has conserved SUMOylation and SUMO-interacting motifs (SIMs), and we observed SUMOylation of SyYVCV βC1 in host plants as a defensive strategy against ubiquitin-mediated degradation. Counteracting this, SIMs encoded in βC1 mediate the degradation of βC1; however, both these PTMs are essential for the function of βC1 protein since SIM and SUMOylation motif mutants failed to promote pathogenicity and viral replication in vivo. SUMOylation in different motifs of βC1 led to functionally distinct outcomes, regulating the stability and function of the βC1 protein, as well as increased global SUMOylation of host proteins.

CONCLUSION

Our results indicate the presence of a novel mechanism mediating a fine balance between defence and counter-defence in which a SIM site is competitively sought for degradation and, as a counter-defence, βC1 undergoes SUMOylation to escape from its degradation.

Genomic Analysis of the SUMO-Conjugating Enzyme and Genes under Abiotic Stress in Potato (Solanum tuberosum L.)

SUMO-conjugating enzymes (SCE) and SUMO (Small Ubiquitin-Like Modifiers) genes are important components of SUMOylation. SCE has a crucial role during the SUMOylation process which acts as a catalyst to transfer SUMO to the target protein. Comprehensive studies on SCE and SUMO have been performed in some plants, but studies on these genes remain limited in potato. This study is aimed at exploring the role of StSCE and StSUMO genes in abiotic stress conditions. Nine and seven putative StSCEs and StSUMO genes, respectively, were identified using different methods and databases available for potato. Chromosomal localization showed that SCE and StSUMO genes are unevenly distributed on 7 different chromosomes. Potato genome database was accessed for the expression profile of StSCE and StSUMO genes, and these genes were differentially expressed in different tissues and organs during different phases of plant growth. The expression patterns on different treatments were further evaluated using qRT-PCR for all the StSCE and StSUMO genes. The expression was upregulated in StSCE1/5/6 and 7 under salt and PEG treatment. StSUMO 1/2 and 4 were upregulated under salt stress whereas StSCE9 and StSUMO2 and 4 were observed downregulated under PEG treatment. The results of this study could be useful to explore the role of StSCE genes in potato improvement.

Crosstalk between Ubiquitination and Other Post-translational Protein Modifications in Plant Immunity

Post-translational modifications (PTMs) are central to the modulation of protein activity, stability, subcellular localization, and interaction with partners. They greatly expand the diversity and functionality of the proteome and have taken the center stage as key players in regulating numerous cellular and physiological processes. Increasing evidence indicates that in addition to a single regulatory PTM, many proteins are modified by multiple different types of PTMs in an orchestrated manner to collectively modulate the biological outcome. Such PTM crosstalk creates a combinatorial explosion in the number of proteoforms in a cell and greatly improves the ability of plants to rapidly mount and fine-tune responses to different external and internal cues. While PTM crosstalk has been investigated in depth in humans, animals, and yeast, the study of interplay between different PTMs in plants is still at its infant stage. In the past decade, investigations showed that PTMs are widely involved and play critical roles in the regulation of interactions between plants and pathogens. In particular, ubiquitination has emerged as a key regulator of plant immunity. This review discusses recent studies of the crosstalk between ubiquitination and six other PTMs, i.e., phosphorylation, SUMOylation, poly(ADP-ribosyl)ation, acetylation, redox modification, and glycosylation, in the regulation of plant immunity. The two basic ways by which PTMs communicate as well as the underlying mechanisms and diverse outcomes of the PTM crosstalk in plant immunity are highlighted.

Overexpression of GmSUMO2 gene confers increased abscisic acid sensitivity in transgenic soybean hairy roots

Small ubiquitin-like modifier (SUMO) participates in post-translational modification of various target proteins. SUMOylation is an important molecular regulatory mechanism for plants to respond to abiotic stress. In the present study, GmSUMO2 gene was isolated from soybean seedlings for further study because of the highest expression level among these six SUMO genes in soybean. qRT-PCR results showed that GmSUMO2 gene were detected in root, leaf, cotyledon, seed root, flower, pod and seed, with the highest transcription level in cotyledon. Moreover, GmSUMO2 gene was transcriptionally regulated by 200 mM NaCl, 42 °C, 25 μM abscisic acid (ABA) and 20% PEG6000 during the 24 h period of treatment. Besides, western blot analysis using AtSUMO1 antibody indicated that the free SUMO levels and SUMOylation dynamics were regulated by ABA stimulus. Functional analysis indicated that overexpression of GmSUMO2 gene in soybean hairy roots accentuated the sensitivity to exogenous ABA. Furthermore, the expression levels of ABI3, ABI5, SnRK1.1 and SnRK1.2 were differentially regulated by GmSUMO2 in transgenic soybean hairy roots. Overall, these results provided a preliminary understanding of molecular characterization, expression and function of GmSUMO2 in soybean.

Absence of Dx2 at Glu-D1 Locus Weakens Gluten Quality Potentially Regulated by Expression of Nitrogen Metabolism Enzymes and Glutenin-Related Genes in Wheat

Absence of high-molecular-weight glutenin subunit (HMW-GS) Dx2 weakens the gluten quality, but it is unclear how the absence of Dx2 has these effects. Thus, we investigated the gluten quality in terms of cytological, physicochemical, and transcriptional characteristics using two near-isogenic lines with Dx2 absent or present at Glu-D1 locus. Cytological observations showed that absence of Dx2 delayed and decreased the accumulation of protein bodies (PBs), where fewer and smaller PBs formed in the endosperm. The activity and gene expression levels of nitrogen assimilation and proteolysis enzymes were lower in HMW-D1a without Dx2 than HMW-D1p with Dx2, and thus less amino acid was transported for protein synthesis in the grains. The expression pattern of genes encoding Glu-1Dx2+1Dy12 was similar to those of three transcription factors, where these genes were significantly down-regulated in HMW-D1a than HMW-D1p. Three genes involving with glutenin polymerization were also down-regulated in HMW-D1a. These results may explain the changes in the glutenin and glutenin macropolymer (GMP) levels during grain development. Therefore, we suggest that the lower nitrogen metabolism capacity and expression levels of glutenin synthesis-related genes in HMW-D1a accounted for the lower accumulation of glutenin, GMP, and PBs, thereby weakening the structural‒thermal properties of gluten.

Defining the function of SUMO system in pod development and abiotic stresses in Peanut

BACKGROUND

Posttranslational modification of proteins by small ubiquitin like modifier (SUMO) proteins play an important role during the developmental process and in response to abiotic stresses in plants. However, little is known about SUMOylation in peanut (Arachis hypogaea L.), one of the world's major food legume crops. In this study, we characterized the SUMOylation system from the diploid progenitor genomes of peanut, Arachis duranensis (AA) and Arachis ipaensis (BB).

RESULTS

Genome-wide analysis revealed the presence of 40 SUMO system genes in A. duranensis and A. ipaensis. Our results showed that peanut also encodes a novel class II isotype of the SCE1, which was previously reported to be uniquely present in cereals. RNA-seq data showed that the core components of the SUMOylation cascade SUMO1/2 and SCE1 genes exhibited pod-specific expression patterns, implying coordinated regulation during pod development. Furthermore, both transcripts and conjugate profiles revealed that SUMOylation has significant roles during the pod development. Moreover, dynamic changes in the SUMO conjugates were observed in response to abiotic stresses.

CONCLUSIONS

The identification and organization of peanut SUMO system revealed SUMOylation has important roles during stress defense and pod development. The present study will serve as a resource for providing new strategies to enhance agronomic yield and reveal the mechanism of peanut pod development.

Specific TCP transcription factors interact with and stabilize PRR2 within different nuclear sub-domains

Plants possess a large set of transcription factors both involved in the control of plant development or in plant stress responses coordination. We previously identified PRR2, a Pseudo-Response Regulator, as a plant-specific CML-interacting partner. We reported that PRR2 acts as a positive actor of plant defense by regulating the production of antimicrobial compounds. Here, we report new data on the interaction between PRR2 and transcription factors belonging to the Teosinte branched Cycloidea and PCF (TCP) family. TCPs have been described to be involved in plant development and immunity. We evaluated the ability of PRR2 to interact with seven TCPs representative of the different subclades of the family. PRR2 is able to interact with TCP13, TCP15, TCP19 and TCP20 in yeast two-hybrid system and in planta interactions were validated for TCP19 and TCP20. Transient expression in tobacco highlighted that PRR2 protein is more easily detected when co-expressed with TCP19 or TC20. This stabilization is associated with a specific sub-nuclear localization of the complex in Cajal bodies or in nuclear speckles according to the interaction of PRR2 with TCP19 or TCP20 respectively. The interaction between PRR2 and TCP19 or TCP20 would contribute to the biological function in specific nuclear compartments.

The rice SUMO conjugating enzymes OsSCE1 and OsSCE3 have opposing effects on drought stress

Posttranslational modification of proteins by the small ubiquitin-related modifier (SUMO) protein is involved in diverse cellular processes. In sumoylation, SUMO-conjugating enzyme (SCE) conjugates SUMO to substrate proteins. Similarly to yeast and animals, Arabidopsis encodes a single SCE gene, but other plants encode at least two SCE genes. In this study, we report the molecular characterization of three Oryza sativa SCE genes. Their levels of expression are commonly upregulated by drought stress but are differentially regulated by hormones and sugars. Only the OsSCE1 gene showed photoperiod- and light-dependent diurnal oscillations in the leaves. Yeast two-hybrid assays showed that OsSCEs do not show SUMO isoform specificity. Three rice OsSCE proteins localize primarily to the nucleus. Interestingly, OsSCE1 is distributed in specific parts of the nucleus and shows sumoylation activities in the absence of a SUMO ligase in E. coli. In addition, overexpression of the OsSCE1 gene alters the biomass and grain yield parameters in transgenic rice plants. Overexpression of the OsSCE3 gene in transgenic rice plants enhances drought stress tolerance. In contrast, OsSCE1-OX transgenic rice plants are hypersensitive to drought stress. Our results suggest that these genes may be involved in different cellular processes.

Regulation of Ubiquitination Is Central to the Phosphate Starvation Response

As sessile organisms, plants have developed numerous strategies to overcome the limiting availability of the essential nutrient phosphate in nature. Recent studies reveal that post-translational modification (PTM) by ubiquitination is an important and central regulation mechanism in the plant phosphate starvation response (PSR). Ubiquitination precisely modulates the stability and trafficking of proteins in response to the heterogeneous phosphate supplement. Induction of autophagy provides novel insights into the molecular mechanisms under phosphate starvation. In this review, we present and discuss novel findings on the regulation of diverse PSRs through ubiquitination. Resolving these regulation mechanisms will pave the way to improve phosphate acquisition and utilization efficiency in crops.

Arabidopsis NSE4 Proteins Act in Somatic Nuclei and Meiosis to Ensure Plant Viability and Fertility

The SMC 5/6 complex together with cohesin and condensin is a member of the structural maintenance of chromosome (SMC) protein family. In non-plant organisms SMC5/6 is engaged in DNA repair, meiotic synapsis, genome organization and stability. In plants, the function of SMC5/6 is still enigmatic. Therefore, we analyzed the crucial δ-kleisin component NSE4 of the SMC5/6 complex in the model plant Arabidopsis thaliana. Two functional conserved Nse4 paralogs (Nse4A and Nse4B) are present in A. thaliana, which may have evolved via gene subfunctionalization. Due to its high expression level, Nse4A seems to be the more essential gene, whereas Nse4B appears to be involved mainly in seed development. The morphological characterization of A. thaliana T-DNA mutants suggests that the NSE4 proteins are essential for plant growth and fertility. Detailed investigations in wild-type and the mutants based on live cell imaging of transgenic GFP lines, fluorescence in situ hybridization (FISH), immunolabeling and super-resolution microscopy suggest that NSE4A acts in several processes during plant development, such as mitosis, meiosis and chromatin organization of differentiated nuclei, and that NSE4A operates in a cell cycle-dependent manner. Differential response of NSE4A and NSE4B mutants after induced DNA double strand breaks (DSBs) suggests their involvement in DNA repair processes.

Exploring the regulatory levels of SUMOylation to increase crop productivity

SUMOylation is an essential post-translational modification that affects several cellular processes, from gene replication to stress response. Studies using the SUMO (de)conjugation machinery have provided evidence regarding its potential to improve crop performance and productivity under normal and adverse conditions. However, the pleiotropic effect of SUMOylation can be a disadvantage in both situations, especially when considering unpredictable environmental conditions caused by climate changes. Here, we discuss the pleiotropic effects caused by disrupting the SUMOylation machinery, and new strategies that may help to overcome pleiotropy. We propose exploring the several regulatory levels of SUMOylation recently revealed, including transcriptional, post-transcriptional regulation by alternative splicing, and post-translational modifications. These new findings may provide valuable tools to increase crop productivity.

Co-overexpression of AVP1 and OsSIZ1 in Arabidopsis substantially enhances plant tolerance to drought, salt, and heat stresses

Abiotic stresses such as water deficit, salt, and heat are major environmental factors that negatively affect plant growth, development, and productivity. Previous studies showed that overexpression of the Arabidopsis vacuolar H⁺-pyrophosphatase gene AVP1 increases salt and water deficit stress tolerance and overexpression of the rice SUMO E3 ligase gene OsSIZ1 improves heat and water deficit stress tolerance in transgenic plants. In this report, the effects of co-overexpression of AVP1 and OsSIZ1 in Arabidopsis on abiotic stress tolerance were studied. It was found that AVP1/OsSIZ1 co-overexpressing plants performed significantly better than AVP1-overexpressing plants and OsSIZ1-overexpressing plants, and produced 100% more seed than wild-type plants under single stress or multiple stress conditions. The increased stress tolerance in AVP1/OsSIZ1 co-overexpressing plants was substantially larger than the increased stress tolerance in AVP1-overexpressing plants and OsSIZ1-overexpressing plants under every abiotic stress condition tested. This research provides the proof-of-concept that crop yields might be substantially improved using this approach.

Detection of SUMOylated Phytochromes in Plants

Posttranslational modifications (PTMs) happen after or during protein translation. Small Ubiquitin-like Modifier (SUMO) proteins are covalently attached to certain lysine residues of the target proteins to modify their activity, stability, or localization. This process is called SUMOylation, which is a reversible PTM: SUMO protease enzymes can cleave SUMOs off the target protein backbone. Although many ubiquitinated proteins are targeted for degradation, SUMOylation does not necessary lead to the degradation of the modified protein but lead to the regulation of various physiological responses. SUMOylation of the examined protein cannot simply be monitored by immunoblotting techniques performed on total protein extracts, due to the SUMO-specific signals derived from other modified molecules. Furthermore, the fact that only a limited fraction of the target protein pool is SUMOylated makes the detection of SUMOylated proteins challenging. This protocol shows how SUMOylated phytochrome B (phyB) molecules can be detected using homologous and heterologous experimental systems in planta.

Apple SUMO E3 ligase MdSIZ1 is involved in the response to phosphate deficiency

In plants, SIZ1 regulates abiotic and biotic stress responses by promoting the SUMOylation of proteins. The apple MdSIZ1 protein has conserved domains similar to those of Arabidopsis AtSIZ1. Real-time fluorescent quantitative analysis showed that MdSIZ1 gene expression was induced by phosphate-deficient conditions. In addition, the level of SUMOylation was also significantly increased under these conditions. The MYB transcription factor MdPHR1 might be a target for the SUMO protein, which is a phosphorus starvation-dependent protein. Subsequently, an MdSIZ1 expression vector was constructed and transformed in Arabidopsis mutant siz1-2 and apple callus. The MdSIZ1 transgenic Arabidopsis partially complemented the defect phenotype of siz1-2 under phosphate-deficient conditions. The survival rate, length of primary root, and number or density of lateral roots were similar between the transgenic lines and wild type (WT). Under phosphate-deficient conditions, the SUMO conjugate and fresh weight of the MdSIZ1 transgenic apple callus were improved compared with WT. The MdSIZ1 transgenic apple callus grew under phosphate-deficient conditions, whereas the MdSIZ1 sense apple callus did not. Therefore, MdSIZ1 is involved in the regulation of the phosphate-deficiency response in apple.

SUMO conjugation to the pattern recognition receptor FLS2 triggers intracellular signalling in plant innate immunity

Detection of conserved microbial patterns by host cell surface pattern recognition receptors (PRRs) activates innate immunity. The FLAGELLIN-SENSITIVE 2 (FLS2) receptor perceives bacterial flagellin and recruits another PRR, BAK1 and the cytoplasmic-kinase BIK1 to form an active co-receptor complex that initiates antibacterial immunity in Arabidopsis. Molecular mechanisms that transmit flagellin perception from the plasma-membrane FLS2-associated receptor complex to intracellular events are less well understood. Here, we show that flagellin induces the conjugation of the SMALL UBIQUITIN-LIKE MODIFIER (SUMO) protein to FLS2 to trigger release of BIK1. Disruption of FLS2 SUMOylation can abolish immune responses, resulting in susceptibility to bacterial pathogens in Arabidopsis. We also identify the molecular machinery that regulates FLS2 SUMOylation and demonstrate a role for the deSUMOylating enzyme, Desi3a in innate immunity. Flagellin induces the degradation of Desi3a and enhances FLS2 SUMOylation to promote BIK1 dissociation and trigger intracellular immune signalling.

The plant FLS2 receptor initiates bacterial immunity in response to flagellin. Here the authors show that SUMO conjugates to FLS2 in response to flagellin promoting downstream signalling events while Desi3A, an FLS2 deSUMOylating enzyme, is degraded to enhance immune responses.

Wheat grain protein accumulation and polymerization mechanisms driven by nitrogen fertilization

In wheat (Triticum aestivum) grain yield and grain protein content are negatively correlated, making the simultaneous increase of the two traits challenging. Apart from genetic approaches, modification of nitrogen fertilization offers a feasible option to achieve this aim. In this study, a range of traits related to nitrogen-use efficiency in six Australian bread wheat varieties were investigated under different nitrogen treatments using 3-year multisite field trials. Changes in the individual storage protein composition were detected by high-performance liquid chromatography. Our results indicated that wheat grain yield and grain protein content reacted similarly to nitrogen availability, with grain yield being slightly more sensitive than grain protein content, and that genotype is a vital determinant of grain protein yield. Measurement of the glutamine synthetase activity of flag leaves and developing grains revealed that high nitrogen availability prompted the participation of glutamine in biological processes. In addition, a more significant accumulation of gluten macropolymer was observed under the high-nitrogen treatment from 21 days post-anthesis, and the underlying mechanism was elucidated by a comparative proteomics study. A yeast two-hybrid experiment confirmed this mechanism. The results of this study revealed that peptidyl-prolyl cis-trans isomerase (PPIase) was SUMOylated with the assistance of small ubiquitin-related modifier 1 and that high nitrogen availability facilitated this connection for the subsequent protein polymerization. Additionally, luminal-binding protein 2 in the endoplasmic reticulum played a similar role to PPIase in the aggregation of protein under high-nitrogen conditions.

Genome-Wide Association Study Reveals Novel Genomic Regions for Grain Yield and Yield-Related Traits in Drought-Stressed Synthetic Hexaploid Wheat

Synthetic hexaploid wheat (SHW; 2n = 6x = 42, AABBDD, Triticum aestivum L.) is produced from an interspecific cross between durum wheat (2n = 4x = 28, AABB, T. turgidum L.) and goat grass (2n = 2x = 14, DD, Aegilops tauschii Coss.) and is reported to have significant novel alleles-controlling biotic and abiotic stresses resistance. A genome-wide association study (GWAS) was conducted to unravel these loci [marker⁻trait associations (MTAs)] using 35,648 genotyping-by-sequencing-derived single nucleotide polymorphisms in 123 SHWs. We identified 90 novel MTAs (45, 11, and 34 on the A, B, and D genomes, respectively) and haplotype blocks associated with grain yield and yield-related traits including root traits under drought stress. The phenotypic variance explained by the MTAs ranged from 1.1% to 32.3%. Most of the MTAs (120 out of 194) identified were found in genes, and of these 45 MTAs were in genes annotated as having a potential role in drought stress. This result provides further evidence for the reliability of MTAs identified. The large number of MTAs (53) identified especially on the D-genome demonstrate the potential of SHWs for elucidating the genetic architecture of complex traits and provide an opportunity for further improvement of wheat under rapidly changing climatic conditions.