SUMO E3 Ligase SIZ1 stabilizes MYB75 to regulate anthocyanin accumulation under high light conditions in Arabidopsis

The E3 ubiquitin ligase BRG3 and the protein kinase MPK7 antagonistically regulate LBD36 turnover, a key node for integrating nitrate and gibberellin signaling in apple

Nitrate is the main source of nitrogen in plants. Nitrate stimulation causes changes in plant secondary metabolites, including anthocyanins. However, the molecular mechanism underlying how nitrate regulates anthocyanin biosynthesis remains unclear. In this study, we identified a nitrate response factor MdLBD36 in apple. This factor positively regulated nitrate deficiency-induced anthocyanin biosynthesis by promoting the transcriptional activity of MdABI5, an important regulator of anthocyanins, and directly activated MdABI5 expression. The E3 ubiquitin ligase MdBRG3 promoted the ubiquitinated degradation of MdLBD36 to reduce anthocyanin biosynthesis under nitrate-sufficient conditions. Nitrate deficiency-activated MdMPK7 maintained the stimulating effect of MdLBD36 on anthocyanin biosynthesis by counteracting the MdBRG3-mediated degradation of MdLBD36. Nitrate coordinated gibberellin (GA) signaling to regulate anthocyanin biosynthesis. The GA signaling repressor MdRGL2a contributed to MdLBD36-promoted anthocyanin biosynthesis by enhancing the MdLBD36-MdABI5 interaction and increasing the MdLBD36 transcriptional activation of MdABI5. In summary, our results elucidate the molecular framework of the coordinated regulation of the nitrate signaling response and anthocyanin biosynthesis by ubiquitination and phosphorylation. This study revealed the cross talk between nitrate and GA signaling in the regulation of anthocyanin biosynthesis and provides references for an in-depth exploration of the nitrate signal transduction pathway and its interactions with hormones.

MYB proteins: Versatile regulators of plant development, stress responses, and secondary metabolite biosynthetic pathways

MYB proteins are ubiquitous in nature, regulating key aspects of plant growth and development. Although MYB proteins are known for regulating genes involved in secondary metabolite biosynthesis, particularly phenylpropanoids, their roles in terpenoid, glucosinolate, and alkaloid biosynthesis remain less understood. This review explores the structural and functional differences between activator and repressor MYB proteins along with their roles in plant growth, development, stress responses, and secondary metabolite production. MYB proteins serve as central hubs in protein-protein interaction networks that regulate expression of numerous genes involved in the adaptation of plants to varying environmental conditions. Thus, we also highlight key interacting partners of MYB proteins and their roles in these adaptation mechanisms. We further discuss the mechanisms regulating MYB proteins, including autoregulation, epigenetics, and post-transcriptional and post-translational modifications. Overall, we propose MYB proteins as versatile regulators for improving plant traits, stress responses, and secondary metabolite production.

Regulation of Flavonoid Biosynthesis by the MYB-bHLH-WDR (MBW) Complex in Plants and Its Specific Features in Cereals

Flavonoids are a large group of secondary metabolites, which are responsible for pigmentation, signaling, protection from unfavorable environmental conditions, and other important functions, as well as providing numerous benefits for human health. Various stages of flavonoid biosynthesis are subject to complex regulation by three groups of transcription regulators-MYC-like bHLH, R2R3-MYB and WDR which form the MBW regulatory complex. We attempt to cover the main aspects of this intriguing regulatory system in plants, as well as to summarize information on their distinctive features in cereals. Published data revealed the following perspectives for further research: (1) In cereals, a large number of paralogs of MYC and MYB transcription factors are present, and their diversification has led to spatial and biochemical specialization, providing an opportunity to fine-tune the distribution and composition of flavonoid compounds; (2) Regulatory systems formed by MBW proteins in cereals possess distinctive features that are not yet fully understood and require further investigation; (3) Non-classical MB-EMSY-like complexes, WDR-independent MB complexes, and solely acting R2R3-MYB transcription factors are of particular interest for studying unique regulatory mechanisms in plants. More comprehensive understanding of flavonoid biosynthesis regulation will allow us to develop cereal varieties with the required flavonoid content and spatial distribution.

Mitogen-activated protein kinase-mediated regulation of plant specialized metabolism

Post-transcriptional and post-translational modification of transcription factors (TFs) and pathway enzymes significantly affect the stress-stimulated biosynthesis of specialized metabolites (SMs). Protein phosphorylation is one of the conserved and ancient mechanisms that critically influences many biological processes including specialized metabolism. The phosphorylation of TFs and enzymes by protein kinases (PKs), especially the mitogen-activated protein kinases (MAPKs), is well studied in plants. While the roles of MAPKs in plant growth and development, phytohormone signaling, and immunity are well elucidated, significant recent advances have also been made in understanding the involvement of MAPKs in specialized metabolism. However, a comprehensive review highlighting the significant progress in the past several years is notably missing. This review focuses on MAPK-mediated regulation of several important SMs, including phenylpropanoids (flavonoids and lignin), terpenoids (artemisinin and other terpenoids), alkaloids (terpenoid indole alkaloids and nicotine), and other nitrogen- and sulfur-containing SMs (camalexin and indole glucosinolates). In addition to MAPKs, other PKs also regulate SM biosynthesis. For comparison, we briefly discuss the regulation by other PKs, such as sucrose non-fermenting-1 (SNF)-related protein kinases (SnRKs) and calcium-dependent protein kinases (CPKs). Furthermore, we provide future perspectives in this active area of research.

Polyvinyl chloride microplastics and drought co-exposure alter rice growth by affecting metabolomics and proteomics

Microplastics, interacting with drought stress, have become threat to crops by altering soil environment. Currently, the effect of combined microplastic and drought stress on crop growth remain poorly understood. In this work, the mechanism of multi-stress responses was investigated under the exposure of polvinylchloride microplastic (PV) and drought (D) individually and in combination (DPV) on rice varieties Hanyou73 and Q280 through proteomics and metabolomic analysis. All treatments negatively affect chlorophyll content, antioxidant enzyme activities, rice grain composition, metabolome and proteomic profiling of both rice varieties. Full rice grain yield was decreased under all treatments except PV treatment in which it was increased in both rice varieties. DPV treatment shows the lowest grain yield and more adverse effects on metabolome by affecting glycerophospholipid metabolism, tryptophan metabolism and alanine, aspartate and glutamate metabolism. Soluble sugar contents were decreased in H73 but in Q280 increased by 159 % under DPV and 123 % in PV treatment, compared to their control group. The results from metabolomics illustrate that glycerophospholipid metabolism is commonly altered in both rice types under all treatments. PV and drought alone and in combination induce extensive alterations in proteomics of rice leaves especially impacting proteins related to binding, translation and photosynthetic process. The results reveal that PV and DPV treatments highly distort the abundance of metabolites and proteins in both rice types, demonstrating that microplastic toxicity effects on rice plants become more severe when combined with drought stress.

A negative feedback regulatory module comprising R3-MYB repressor MYBL2 and R2R3-MYB activator PAP1 fine-tunes high light-induced anthocyanin biosynthesis in Arabidopsis

Anthocyanins, a group of flavonoids, play diverse roles in plant growth and environmental adaptation. The biosynthesis and accumulation of anthocyanin are regulated by environmental cues, such as high light. However, the precise mechanism underlying anthocyanin biosynthesis under high light conditions remains largely unclear. Here, we report that the R3-MYB repressor MYB-LIKE 2 (MYBL2) negatively regulates high light-induced anthocyanin biosynthesis in Arabidopsis by repressing two R2R3-MYB activators, PRODUCTION OF ANTHOCYANIN PIGMENT 1 (PAP1) and PAP2, which are core components of the MYB-bHLH-WD40 (MBW) complex. We found that MYBL2 interacts with PAP1/2 and reduces their transcriptional activation activities, thus disrupting the expression of key genes involved in anthocyanin biosynthesis, such as DIHYDROFLAVONOL 4-REDUCTASE (DFR) and TRANSPARENT TESTA 19 (TT19). Additionally, MYBL2 attenuates the transcriptional activation of PAP1 and its own expression, but not that of PAP2. Conversely, PAP1 collaborates with TRANSPARENT TESTA 8 (TT8), a bHLH member of the MBW complex, to activate MYBL2 transcription when excessive anthocyanins are accumulated. Taken together, our findings reveal a negative feedback regulatory module composed of MYBL2 and PAP1 that fine-tunes high light-induced anthocyanin biosynthesis through modulating MBW complex assembly.

Transcription factors LvBBX24 and LvbZIP44 coordinated anthocyanin accumulation in response to light in lily petals

Lily (Lilium spp.), a horticultural crop serving both ornamental and edible functions, derives its coloration primarily from anthocyanins. However, limited studies have been conducted on the accumulation of anthocyanins within lilies. In this study, we cloned a light-induced transcription factor named as LvBBX24 in lilies. Through genetic and biochemical analysis, we determined that LvBBX24 could upregulate the transcription of LvMYB5 and facilitate anthocyanin synthesis. Moreover, we identified that darkness promoted the degradation of LvBBX24 protein. Through screening a yeast library, we identified LvbZIP44 acts as its interacting partner. Genetic testing confirmed that LvbZIP44 also plays a role in promoting lily anthocyanin synthesis. This indicates a potential synergistic regulatory effect between LvBBX24 and LvbZIP44. Our study indicates that LvBBX24 and LvbZIP44 cooperate to regulate anthocyanin accumulation in lily petals. These findings provide compelling evidence supporting the idea that LvBBX24 and LvbZIP44 may form a looped helix surrounding the LvMYB5 promoter region to regulate anthocyanin biosynthesis.

Transcription factors BZR1 and PAP1 cooperate to promote anthocyanin biosynthesis in Arabidopsis shoots

Anthocyanins play critical roles in protecting plant tissues against diverse stresses. The complicated regulatory networks induced by various environmental factors modulate the homeostatic level of anthocyanins. Here, we show that anthocyanin accumulation is induced by brassinosteroids (BRs) in Arabidopsis (Arabidopsis thaliana) shoots and shed light on the underlying regulatory mechanism. We observed that anthocyanin levels are altered considerably in BR-related mutants, and BRs induce anthocyanin accumulation by upregulating the expression of anthocyanin biosynthetic genes. Our genetic analysis indicated that BRASSINAZOLE RESISTANT 1 (BZR1) and PRODUCTION OF ANTHOCYANIN PIGMENT 1 (PAP1) are essential for BR-induced anthocyanin accumulation. The BR-responsive transcription factor BZR1 directly binds to the PAP1 promoter, regulating its expression. In addition, we found that intense anthocyanin accumulation caused by the pap1-D-dominant mutation is significantly reduced in BR mutants, implying that BR activity is required for PAP1 function after PAP1 transcription. Moreover, we demonstrated that BZR1 physically interacts with PAP1 to cooperatively regulate the expression of PAP1-target genes, such as TRANSPARENT TESTA 8, DIHYDROFLAVONOL 4-REDUCTASE, and LEUKOANTHOCYANIDIN DIOXYGENASE. Our findings indicate that BZR1 functions as an integral component of the PAP1-containing transcription factor complex, contributing to increased anthocyanin biosynthesis. Notably, we also show that functional interaction of BZR1 with PAP1 is required for anthocyanin accumulation induced by low nitrogen stress. Taken together, our results demonstrate that BR-regulated BZR1 promotes anthocyanin biosynthesis through cooperative interaction with PAP1 of the MBW complex.

Interaction of ubiquitin-like protein SILENCING DEFECTIVE 2 with LIKE HETEROCHROMATIN PROTEIN 1 is required for regulation of anthocyanin biosynthesis in Arabidopsis thaliana in response to sucrose

The regulatory mechanisms of anthocyanin biosynthesis have been well documented at the transcriptional and translational levels. By contrast, how anthocyanin biosynthesis is epigenetically regulated remains largely unknown. In this study, we employed genetic, molecular biology, and chromatin immunoprecipitation-quantitative polymerase chain reaction assays to identify a regulatory module essential for repressing the expression of genes involved in anthocyanin biosynthesis through chromatin remodeling. We found that SILENCING DEFECTIVE 2 (SDE2), which was previously identified as a negative regulator for sucrose-induced anthocyanin accumulation in Arabidopsis, is cleaved into N-terminal SDE2-UBL and C-terminal SDE2-C fragments at the first diglycine motif, and the cleaved SDE2-C, which can fully complement the sde2 mutant, is localized in the nucleus and physically interacts with LIKE HETEROCHROMATIN PROTEIN 1 (LHP1) in vitro and in vivo. Genetic analyses showed that both SDE2 and LHP1 act as negative factors for anthocyanin biosynthesis. Consistently, immunoblot analysis revealed that the level of LHP1-bound histone H3 lysine 27 trimethylation (H3K27me3) significantly decreases in sde2 and lhp1 mutants, compared to wild-type (WT). In addition, we found that sugar can induce expression of SDE2 and LHP1, and enhance the level of the nucleus-localized SDE2-C. Taken together, our data suggest that the SDE2-C-LHP1 module is required for repression of gene expression through H3K27me3 modification during sugar-induced anthocyanin biosynthesis in Arabidopsis thaliana.

MdWER interacts with MdERF109 and MdJAZ2 to mediate methyl jasmonate- and light-induced anthocyanin biosynthesis in apple fruit

Anthocyanin generation in apples (Malus domestica) and the pigmentation that results from it may be caused by irradiation and through administration of methyl jasmonate (MeJA). However, their regulatory interrelationships associated with fruit coloration are not well defined. To determine whether MdERF109, a transcription factor (TF) involved in light-mediated coloration and anthocyanin biosynthesis, has synergistic effects with other proteins, we performed a yeast two-hybrid assessment and identified another TF, MdWER. MdWER was induced by MeJA treatment, and although overexpression of MdWER alone did not promote anthocyanin accumulation co-overexpression with MdERF109 resulted in significantly increase in anthocyanin biosynthesis. MdWER may form a protein complex with MdERF109 to promote anthocyanin accumulation by enhancing combinations between the proteins and their corresponding genes. In addition, MdWER, as a MeJA responsive protein, interacts with the anthocyanin repressor MdJAZ2. Transient co-expression in apple fruit and protein interaction assays allowed us to conclude that MdERF109 and MdJAZ2 interact with MdWER and take part in the production of anthocyanins upon MeJA treatment and irradiation. Our findings validate a role for the MdERF109-MdWER-MdJAZ2 module in anthocyanin biosynthesis and uncover a novel mechanism for how light and MeJA signals are coordinated anthocyanin biosynthesis in apple fruit.

RHA2b-mediated MYB30 degradation facilitates MYB75-regulated, sucrose-induced anthocyanin biosynthesis in Arabidopsis seedlings

Anthocyanins play diverse roles in plant physiology and stress adaptation. In Arabidopsis, the MYB-bHLH-WD40 (MBW) complex has a crucial role in the regulation of anthocyanin synthesis. Here, we report that the R2R3-MYB transcription factor MYB30 and the ubiquitin E3 ligase RHA2b participate in anthocyanin biosynthesis through regulation of the MBW complex. MYB30 was found to negatively regulate sucrose-induced anthocyanin biosynthesis in Arabidopsis seedlings. Expression of multiple genes involved in flavonoid or anthocyanin biosynthesis was affected in the myb30 mutant, and MYB30 directly repressed the expression of MYB75, which encodes a core component of the MBW complex, by binding to its promoter. Moreover, MYB30 physically interacted with MYB75 to inhibit its activity by repressing MBW complex assembly. In addition, sucrose treatment significantly promoted MYB30 degradation via the action of RHA2b. The ubiquitination and degradation of MYB30 were significantly attenuated in the rha2b mutant under high-sucrose treatment, and further analysis showed that MYB75 directly promoted RHA2b expression in response to high sucrose. Our work thus reveals an anthocyanin biosynthetic regulatory module, RHA2b-MYB30, that controls the function of the MBW complex via MYB75. The repression of MYB75 by MYB30 is released by MYB75-induced RHA2b expression, thus ensuring the self-activation of MYB75 when anthocyanin synthesis is needed.

Role of epigenetic and post-translational modifications in anthocyanin biosynthesis: A review

Anthocyanins are a class of flavonoids having antioxidant and anti-inflammatory properties. They defend plants against various biotic and abiotic stresses and are synthesized by a specific branch of the flavonoid biosynthetic pathway. Different regulatory mechanisms have been found to regulate anthocyanin biosynthesis in plants. These include the MYB-bHLH-WDR (MBW) MBW trimeric complex consisting of bHLH, R2R3 MYB, and WD40 transcription factors. Epigenetic and Post-translational modification (PTMs) of MBW complex and various other transcription factors play important role in both plant developmental processes and modulating plant response to different environmental conditions. Recent studies have broadened our understanding of the role of various epigenetic (methylation and histone modification) and PTMs (phosphorylation, acetylation, ubiquitylation, sumoylation, etc.) mechanisms in regulating anthocyanin biosynthesis in plants. In this review, we are updating various epigenetic and PTMs modifications of various transcription factors which regulate anthocyanin biosynthesis in various plants. In addition to this, we have also briefly discussed in which direction future research on epigenetic and PTMs can be taken so that we can engineer medicinal plants for enhanced secondary metabolite biosynthesis.

Light regulation of the biosynthesis of phenolics, terpenoids, and alkaloids in plants

Biosynthesis of specialized metabolites (SM), including phenolics, terpenoids, and alkaloids, is stimulated by many environmental factors including light. In recent years, significant progress has been made in understanding the regulatory mechanisms involved in light-stimulated SM biosynthesis at the transcriptional, posttranscriptional, and posttranslational levels of regulation. While several excellent recent reviews have primarily focused on the impacts of general environmental factors, including light, on biosynthesis of an individual class of SM, here we highlight the regulation of three major SM biosynthesis pathways by light-responsive gene expression, microRNA regulation, and posttranslational modification of regulatory proteins. In addition, we present our future perspectives on this topic.

SnRK1 inhibits anthocyanin biosynthesis through both transcriptional regulation and direct phosphorylation and dissociation of the MYB/bHLH/TTG1 MBW complex

Plants have evolved an extensive specialized secondary metabolism. The colorful flavonoid anthocyanins, for example, not only stimulate flower pollination and seed dispersal, but also protect different tissues against high light, UV and oxidative stress. Their biosynthesis is highly regulated by environmental and developmental cues and induced by high sucrose levels. Expression of the biosynthetic enzymes involved is controlled by a transcriptional MBW complex, comprising (R2R3) MYB- and bHLH-type transcription factors and the WD40 repeat protein TTG1. Anthocyanin biosynthesis is not only useful, but also carbon- and energy-intensive and non-vital. Consistently, the SnRK1 protein kinase, a metabolic sensor activated in carbon- and energy-depleting stress conditions, represses anthocyanin biosynthesis. Here we show that Arabidopsis SnRK1 represses MBW complex activity both at the transcriptional and post-translational level. In addition to repressing expression of the key transcription factor MYB75/PAP1, SnRK1 activity triggers MBW complex dissociation, associated with loss of target promoter binding, MYB75 protein degradation and nuclear export of TTG1. We also provide evidence for direct interaction with and phosphorylation of multiple MBW complex proteins. These results indicate that repression of expensive anthocyanin biosynthesis is an important strategy to save energy and redirect carbon flow to more essential processes for survival in metabolic stress conditions.

High light triggers flavonoid and polysaccharide synthesis through DoHY5-dependent signaling in Dendrobium officinale

Dendrobium officinale is edible and has medicinal and ornamental functions. Polysaccharides and flavonoids, including anthocyanins, are important components of D. officinale that largely determine the nutritional quality and consumer appeal. There is a need to study the molecular mechanisms regulating anthocyanin and polysaccharide biosynthesis to enhance D. officinale quality and its market value. Here, we report that high light (HL) induced the accumulation of polysaccharides, particularly mannose, as well as anthocyanin accumulation, resulting in red stems. Metabolome and transcriptome analyses revealed that most of the flavonoids showed large changes in abundance, and flavonoid and polysaccharide biosynthesis was significantly activated under HL treatment. Interestingly, DoHY5 expression was also highly induced. Biochemical analyses demonstrated that DoHY5 directly binds to the promoters of DoF3H1 (involved in anthocyanin biosynthesis), DoGMPP2, and DoPMT28 (involved in polysaccharide biosynthesis) to activate their expression, thereby promoting anthocyanin and polysaccharide accumulation in D. officinale stems. DoHY5 silencing decreased flavonoid- and polysaccharide-related gene expression and reduced anthocyanin and polysaccharide accumulation, whereas DoHY5 overexpression had the opposite effects. Notably, naturally occurring red-stemmed D. officinale plants similarly have high levels of anthocyanin and polysaccharide accumulation and biosynthesis gene expression. Our results reveal a previously undiscovered role of DoHY5 in co-regulating anthocyanin and polysaccharide biosynthesis under HL conditions, improving our understanding of the mechanisms regulating stem color and determining nutritional quality in D. officinale. Collectively, our results propose a robust and simple strategy for significantly increasing anthocyanin and polysaccharide levels and subsequently improving the nutritional quality of D. officinale.

Genome-wide association analysis provides insights into the genetic basis of photosynthetic responses to low-temperature stress in spring barley

Low-temperature stress (LTS) is among the major abiotic stresses affecting the geographical distribution and productivity of the most important crops. Understanding the genetic basis of photosynthetic variation under cold stress is necessary for developing more climate-resilient barley cultivars. To that end, we investigated the ability of chlorophyll fluorescence parameters (F_VF_M, and F_VF₀) to respond to changes in the maximum quantum yield of Photosystem II photochemistry as an indicator of photosynthetic energy. A panel of 96 barley spring cultivars from different breeding zones of Canada was evaluated for chlorophyll fluorescence-related traits under cold acclimation and freeze shock stresses at different times. Genome-wide association studies (GWAS) were performed using a mixed linear model (MLM). We identified three major and putative genomic regions harboring 52 significant quantitative trait nucleotides (QTNs) on chromosomes 1H, 3H, and 6H for low-temperature tolerance. Functional annotation indicated several QTNs were either within the known or close to genes that play important roles in the photosynthetic metabolites such as abscisic acid (ABA) signaling, hydrolase activity, protein kinase, and transduction of environmental signal transduction at the posttranslational modification levels. These outcomes revealed that barley plants modified their gene expression profile in response to decreasing temperatures resulting in physiological and biochemical modifications. Cold tolerance could influence a long-term adaption of barley in many parts of the world. Since the degree and frequency of LTS vary considerably among production sites. Hence, these results could shed light on potential approaches for improving barley productivity under low-temperature stress.

Inhibition of SIZ1-mediated SUMOylation of HOOKLESS1 promotes light-induced apical hook opening in Arabidopsis

The apical hook protects cotyledons and the shoot apical meristem from mechanical injuries during seedling emergence from the soil. HOOKLESS1 (HLS1) is a central regulator of apical hook development, as a terminal signal onto which several pathways converge. However, how plants regulate the rapid opening of the apical hook in response to light by modulating HLS1 function remains unclear. In this study, we demonstrate that the small ubiquitin-like modifier (SUMO) E3 ligase SAP AND MIZ1 DOMAIN-CONTAINING LIGASE1 (SIZ1) interacts with HLS1 and mediates its SUMOylation in Arabidopsis thaliana. Mutating SUMO attachment sites of HLS1 results in impaired function of HLS1, indicating that HLS1 SUMOylation is essential for its function. SUMOylated HLS1 was more likely to assemble into oligomers, which are the active form of HLS1. During the dark-to-light transition, light induces rapid apical hook opening, concomitantly with a drop in SIZ1 transcript levels, resulting in lower HLS1 SUMOylation. Furthermore, ELONGATED HYPOCOTYL5 (HY5) directly binds to the SIZ1 promoter and suppresses its transcription. HY5-initiated rapid apical hook opening partially depended on HY5 inhibition of SIZ1 expression. Taken together, our study identifies a function for SIZ1 in apical hook development, providing a dynamic regulatory mechanism linking the post-translational modification of HLS1 during apical hook formation and light-induced apical hook opening.

Comprehensive insight into an amino acid metabolic network in postharvest horticultural products: a review

Amino acid (AA) metabolism plays a vital role in the central metabolism of plants. In addition to protein biosynthesis, AAs are involved in secondary metabolite biosynthesis, signal transduction, stress response, defense against pathogens, flavor formation, and so on. Besides these functions, AAs can be degraded into precursors or intermediates of the tricarboxylic acid cycle to substitute respiratory substrates and restore energy homeostasis, as well as directly acting as signal molecules or be involved in the regulation of plant signals to delay senescence of postharvest horticultural products (PHPs). AA metabolism and its role in plants growth have been clarified; however, only a few studies about their roles exist concerning the postharvest preservation of fruit and vegetables. This study reviews the potential functions of various AAs by comparing the difference in AA metabolism at the postharvest stage and then discusses the crosstalk of AA metabolism and energy metabolism, the target of rapamycin/sucrose nonfermenting-related kinase 1 signaling and secondary metabolism. Finally, the roles and effect mechanism of several exogenous AAs in the preservation of PHPs are highlighted. This review provides a comprehensive insight into the AA metabolism network in PHPs. © 2023 Society of Chemical Industry.

SUMOylation regulates low-temperature survival and oxidative DNA damage tolerance in Botrytis cinerea

SUMOylation as one of the protein post-translational modifications plays crucial roles in multiple biological processes of eukaryotic organisms. Botrytis cinerea is a devastating fungal pathogen and capable of infecting plant hosts at low temperature. However, the molecular mechanisms of low-temperature adaptation are largely unknown in fungi. Combining with biochemical methods and biological analyses, we report that SUMOylation regulates pathogen survival at low temperature and oxidative DNA damage response during infection in B. cinerea. The heat shock protein (Hsp70) BcSsb and E3 ubiquitin ligase BcRad18 were identified as substrates of SUMOylation; moreover, their SUMOylation both requires a single unique SUMO-interacting motif (SIM). SUMOylated BcSsb regulates β-tubulin accumulation, thereby affecting the stability of microtubules and consequently mycelial growth at low temperature. On the contrary, SUMOylated BcRad18 modulates mono-ubiquitination of the sliding clamp protein proliferating cell nuclear antigen (PCNA), which is involved in response to oxidative DNA damage during infection. Our study uncovers the molecular mechanisms of SUMOylation-mediated low-temperature survival and oxidative DNA damage tolerance during infection in a devastating fungal pathogen, which provides novel insights into low-temperature adaptation and pathogenesis for postharvest pathogens as well as new targets for inhibitor invention in disease control.

Post-translational modifications: emerging regulators manipulating jasmonate biosynthesis and signaling

Jasmonate (JA) is one of the key phytohormones essential for plant development and defense processes. The core JA biosynthetic and signaling pathways have been well-characterized. Notably, post-translational modifications (PTMs), which affect the protein structures and functions, have emerged as critical mechanisms to modulate JA output at different spatiotemporal levels. Disruption of PTMs in JA biosynthesis and signaling would cause the dysfunction of vital biological processes. Here, we give an overview of the PTMs that have been identified in JA biosynthetic and signaling pathways, and provide insights into the mechanisms by which PTMs define JA responses.

Arabidopsis SUMO E3 ligase SIZ1 enhances cadmium tolerance via the glutathione-dependent phytochelatin synthesis pathway

Sumoylation is a posttranslational modification (PTM) in which SUMO (small ubiquitin-like modifier) is covalently conjugated to protein substrates via a range of enzymes. SUMO E3 ligase SIZ1 is involved in mediating several essential or nonessential element-responsive SUMO conjugations in Arabidopsis. However, whether SIZ1 is involved in the cadmium (Cd) response remains to be identified. In this study, we found that SIZ1 positively regulates plant Cd tolerance. The loss-of-function siz1-2 mutant exhibited impaired resistance to Cd exposure and accumulated more reactive oxygen species (ROS). Moreover, the transcription of GSH1, GSH2, PCS1, and PCS2 was suppressed while the accumulation of Cd was enhanced in the siz1-2 mutant under Cd exposure. Further analysis revealed that the higher Cd sensitivity of the siz1-2 mutant was partially rescued by the overexpression of GSH1. Consistently, Cd stress stimulated the accumulation of SUMO1 conjugates in wild-type plants but not in the siz1-2 mutant. Together, our results demonstrate that Cd-induced SIZ1 activates GSH- and PC synthesis-related gene expression to increase the synthesis of GSH- and PCs, thereby leading to higher Cd tolerance in plants.

Review: Exploring possible approaches using ubiquitylation and sumoylation pathways in modifying plant stress tolerance

Ubiquitin and similar proteins, such as SUMO, are utilized by plants to modify target proteins to rapidly change their stability and activity in cells. This review will provide an overview of these crucial protein interactions with a focus on ubiquitylation and sumoylation in plants and how they contribute to stress tolerance. The work will also explore possibilities to use these highly conserved pathways for novel approaches to generate more robust crop plants better fit to cope with abiotic and biotic stress situations.

Synergetic modulation of plant cadmium tolerance via MYB75-mediated ROS homeostasis and transcriptional regulation

KEY MESSAGE

MYB75 enhances plant cadmium tolerance by mediating ROS homeostasis and cadmium tolerance-related genes expression. Cadmium (Cd) is a heavy metal with biological toxicity, which can be detoxified through chelation and compartmentation in plants. Transcriptional regulation mediates plant Cd tolerance by modulating these processes. However, the mechanism remains to be studied. Our results showed a previously unknown function of MYB75 transcription factor in the regulation of Cd tolerance. Cd exposure stimulates anthocyanin accumulation by raising MYB75 expression. Enhanced Cd tolerance was observed in the MYB75-overexpressing plants, whereas increased Cd sensitivity was found in the MYB75 loss-of-function mutants. Under Cd stress conditions, lower reactive oxygen species (ROS) levels were detected in MYB75-overexpressing plants than in wild type plants. In contrast, higher ROS levels were found in MYB75 loss-of-function mutants. Overexpression of MYB75 was associated with increased glutathione (GSH) and phytochelatin (PC) content under Cd exposure. Furthermore, the expression of Cd stress-related gene including ACBP2 and ABCC2 was elevated in MYB75-overexpressing plants, and this upregulation was mediated through the mechanism by which MYB75 directly bind to the promoter of ACBP2 and ABCC2. Our findings reveal an important role for MYB75 in the regulation of plant Cd tolerance via anthocyanin-mediated ROS homeostasis, and through upregulation of Cd stress-related gene at the transcriptional level.

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.

Phytosulfokine α (PSKα) delays senescence and reinforces SUMO1/SUMO E3 ligase SIZ1 signaling pathway in cut rose flowers (Rosa hybrida cv. Angelina)

Roses are widely used as cut flowers worldwide. Petal senescence confines the decorative quality of cut rose flowers, an impressively considerable economic loss. Herein, we investigated the SUMO1/SUMO E3 ligase SIZ1 signaling pathway during bud opening, and petal senescence of cut rose flowers. Our results exhibited that the higher expression of SUMO1 and SUMO E3 ligase SIZ1 during bud opening was accompanied by lower endogenous H2O2 accumulation arising from higher expression and activities of SOD, CAT, APX, and GR, promoting proline accumulation by increasing P5CS expression and activity and enhancing GABA accumulation by increasing GAD expression and activity. In harvested flowers, lower expressions of SUMO1 and SUMO E3 ligase SIZ1 during petal senescence were associated with higher endogenous H2O2 accumulation due to lower expression and activities of SOD, CAT, APX, and GR. Therefore, promoting the activity of the GABA shunt pathway as realized by higher expression and activities of GABA-T and SSADH accompanied by increasing OAT expression and activity for sufficiently supply proline in rose flowers during petal senescence might serve as an endogenous antisenescence mechanism for slowing down petals senescence by avoiding endogenous H2O2 accumulation. Following phytosulfokine α (PSKα) application, postponing petal senescence in cut rose flowers could be ascribed to higher expression of SUMO1 and SUMO E3 ligase SIZ1 accompanied by higher expression and activities of SOD, CAT, APX, and GR, higher activity of GABA shunt pathway as realized by higher expression and activities of GAD, GABA-T, and SSADH, higher expression and activities of P5CS and OAT for supplying proline and higher expression of HSP70 and HSP90. Therefore, our results highlight the potential of the PSKα as a promising antisenescence signaling peptide in the floriculture industry for postponing senescence and extending the vase life of cut rose flowers.

SUMOylation in Phytopathogen Interactions: Balancing Invasion and Resistance

Plants are constantly confronted by a multitude of biotic stresses involving a myriad of pathogens. In crops, pathogen infections result in significant agronomical losses worldwide posing a threat to food security. In order to enter plant tissues and establish a successful infection, phytopathogens have to surpass several physical, and chemical defense barriers. In recent years, post-translational modification (PTM) mechanisms have emerged as key players in plant defense against pathogens. PTMs allow a highly dynamic and rapid response in front of external challenges, increasing the complexity and precision of cellular responses. In this review, we focus on the role of SUMO conjugation (SUMOylation) in plant immunity against fungi, bacteria, and viruses. In plants, SUMO regulates multiple biological processes, ranging from development to responses arising from environmental challenges. During pathogen attack, SUMO not only modulates the activity of plant defense components, but also serves as a target of pathogen effectors, highlighting its broad role in plant immunity. Here, we summarize known pathogenic strategies targeting plant SUMOylation and, the plant SUMO conjugates involved in host-pathogen interactions. We also provide a catalog of candidate SUMO conjugates according to their role in defense responses. Finally, we discuss the complex role of SUMO in plant defense, focusing on key biological and experimental aspects that contribute to some controversial conclusions, and the opportunities for improving agricultural productivity by engineering SUMOylation in crop species.

SUMOylation: A critical transcription modulator in plant cells

Gene transcription is critical for various cellular processes and is precisely controlled at multiple levels, and posttranslational modification (PTM) is a fast and powerful way to regulate transcription factors (TFs). SUMOylation, which conjugates small ubiquitin-related modifier (SUMO) molecules to protein substrates, is a crucial PTM that modulates the activity, stability, subcellular localization, and partner interactions of TFs in plant cells. Here, we summarize the mechanisms of SUMOylation in the regulation of transcription in plant development and stress responses. We also discuss the crosstalk between SUMOylation and other PTMs, as well as the potential functions of SUMOylation in the regulation of transcription-associated complexes on plant chromatin. This summary and perspective will improve understanding of the molecular mechanism of PTMs in plant transcription regulation.

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.