A Tripartite Amplification Loop Involving the Transcription Factor WRKY75, Salicylic Acid, and Reactive Oxygen Species Accelerates Leaf Senescence

MYB47 delays leaf senescence by modulating jasmonate pathway via direct regulation of CYP94B3/CYP94C1 expression in Arabidopsis

Leaf senescence is a complex genetic process intricately regulated by multiple layers of control. Transcription factors, as master regulators of gene expression, play crucial roles in initiating and progressing leaf senescence. Through screening an activation-tagged mutant library, we identified MYB47 as a negative regulator of leaf senescence. Constitutive or inducible overexpression of MYB47 significantly delays leaf senescence, while loss-of-function mutants exhibit accelerated senescence. Transcriptome analysis revealed a marked suppression of jasmonic acid (JA) signaling in MYB47 overexpression lines. Conversely, the myb47 mutants display elevated JA levels and reduced expression of JA catabolic genes, CYP94B3 and CYP94C1. Biochemical evidence demonstrated that MYB47 directly binds to the promoters of CYP94B3 and CYP94C1, upregulating their expression. Consequently, JA contents are significantly reduced in MYB47 overexpression lines. Overexpressing CYP94B3 or CYP94C1 in myb47 mutants alleviates their early senescence phenotype. Furthermore, JA induces MYB47 expression, forming a negative feedback loop (JA-MYB47-CYP94B3/C1-JA) that fine-tunes leaf senescence. Our findings reveal a novel regulatory module involving MYB47 and JA signaling that governs leaf senescence. By stimulating JA catabolism and attenuating JA signaling, MYB47 plays a crucial role in delaying leaf senescence.

The kinase ATM delays Arabidopsis leaf senescence by stabilizing the phosphatase MKP2 in a phosphorylation-dependent manner

Arabidopsis thaliana (Arabidopsis) Ataxia Telangiectasia Mutated (ATM) kinase plays a vital role in orchestrating leaf senescence; however, the precise mechanisms remain elusive. Here, our study demonstrates that ATM kinase activity is essential for mitigating age- and reactive oxygen species-induced senescence, as restoration of wild-type ATM reverses premature senescence in the atm mutant, while a kinase-dead ATM variant is ineffective. ATM physically interacts with and phosphorylates Mitogen-Activated Protein Kinase Phosphatase 2 (MKP2) to enhance stability under oxidative stress. Mutations in putative phosphorylation sites S15/154 on MKP2 disrupt its phosphorylation, stability, and senescence-delaying function. Moreover, mutation of mitogen-activated protein kinase 6, a downstream target of MKP2, alleviates the premature senescence phenotype of the atm mutant. Notably, the dual-specificity protein phosphatase 19 (HsDUSP19), a predicted human counter protein of MPK2, interacts with both ATM and HsATM and extends leaf longevity in Arabidopsis when overexpressed. These findings elucidate the molecular mechanisms underlying the role of ATM in leaf senescence and suggest that the ATM-MKP2 module is likely evolutionarily conserved in regulating the aging process across eukaryotes.

FaNAC047-FaNAC058 module coordinately promotes chlorophyll degradation and reactive oxygen species production during heat-induced leaf senescence in tall fescue

Leaf senescence can be triggered by various abiotic stresses. Among these, heat stress emerges as a pivotal environmental factor, particularly in light of the predicted rise in global temperatures. However, the molecular mechanism underlying heat-induced leaf senescence remains largely unexplored. As a cool-season grass species, tall fescue (Festuca arundinacea) is an ideal and imperative material for investigating heat-induced leaf senescence because heat stress easily triggers leaf senescence to influence its forage yield and turf quality. Here, we investigated the role of FaNAC047 in heat-induced leaf senescence. Overexpression of FaNAC047 promoted heat-induced leaf senescence in transgenic tall fescue that was evidenced by a more seriously destructive photosystem and higher accumulation of reactive oxygen species (ROS), whereas knockdown of FaNAC047 delayed leaf senescence. Further protein-DNA interaction assays indicated that FaNAC047 directly activated the transcriptions of NON-YELLOW COLORING 1 (FaNYC1), NYC1-like (FaNOL), and STAY-GREEN (FaSGR) but directly inhibited Catalases 2 (FaCAT2) expression, thereby promoting chlorophyll degradation and ROS accumulation. Subsequently, protein-protein interaction assays revealed that FaNAC047 physically interacted with FaNAC058 to enhance its regulatory effect on FaNYC1, FaNOL, FaSGR, and FaCAT2. Additionally, FaNAC047 could transcriptionally activate FaNAC058 expression to form a regulatory cascade, driving senescence progression. Consistently, the knockdown of FaNAC058 significantly delayed heat-induced leaf senescence. Collectively, our results reveal that FaNAC047-FaNAC058 module coordinately mediates chlorophyll degradation and ROS production to positively regulate heat-induced leaf senescence. The findings illustrate the molecular network of heat-induced leaf senescence for breeding heat-resistant plants.

BrWRKY8: a key regulatory factor involved in delaying postharvest leaf senescence of Pakchoi (Brassica rapa subsp. chinensis) by 2,4-epibrassinolide

Brassinosteroids (BRs) are extensively distributed in plants and play crucial roles throughout all stages of plant growth. Nevertheless, the molecular mechanism through which BRs influence postharvest senescence in pakchoi remains elusive. Previous studies have demonstrated that the application of 1.5 μM of the BRs analog 2,4-epibrassinolide (EBR) delayed the leaf senescence in harvested pakchoi. In this study, we constructed the EBR-delayed senescence transcriptome in pakchoi leaves and discovered that EBR modulates the expression of genes involved in the chlorophyll (Chl) metabolism pathway and the BRs pathway in pakchoi. Notably, we identified and characterized an EBR-suppressed, nucleus-localized WRKY transcription factor called BrWRKY8. BrWRKY8 is a highly expressed transcriptional activator in senescent leaves, targeting the promoters of the Chl degradation-associated gene BrSGR2 and the BRs degradation-associated gene BrCHI2, thereby promoting their expression. Overexpression of the BrWRKY8 gene accelerated the senescence process in Arabidopsis leaves, while EBR treatment mitigated the leaf senescence phenotype induced by BrWRKY8 overexpression. Conversely, silencing of BrWRKY8 through the virus-induced gene silencing extended the postharvest storage period of pakchoi. In conclusion, the newly discovered BRs-BrWRKY8 regulatory model in this study provides novel insights into BRs-mediated leaf senescence in pakchoi.

Warm temperature and mild drought remodel transcriptome and alter Arabidopsis responses to mite herbivory

In the context of climate change, increased temperature and decreased water availability are expected to have profound effects on plant-herbivore interactions. To gain further insight into this issue, this work focuses on the dissection of the response of the Arabidopsis thaliana plant to the mite pest Tetranychus urticae under environmental conditions that resemble climate change. Phenotypical and molecular changes were analyzed in plants grown under mild drought and/or warm temperatures. When the transcriptome results were compared in standard and altered climate conditions, a large number of genes were found to be differentially expressed. Mite infestations in these plants showed that basal alterations conditioned the subsequent response of the plant to a specific biotic stressor. Warm temperatures favored mite performance and decreased jasmonic acid accumulation. Reduced plant damage in mild drought conditions was correlated with a higher jasmonic acid accumulation and the up-regulation of many genes involved in the production of defensive compounds. In conclusion, the use of ambient conditions that resemble climate change highlighted the drastic alterations in gene expression that may occur in nature. Understanding how these changes affect specific plant-herbivore interactions is crucial to determining how global warming will affect crop production in the future.

WRKY75-mediated transcriptional regulation of OASA1 controls leaf senescence in Arabidopsis

Cysteine plays a crucial role in various processes throughout plant growth and development stages. The gene OASA1 can produce cysteine in Arabidopsis. However, the potential developmental roles of OASA1 have not been explored during senescence. In the present study, the gene OASA1 showed increasing expression during senescence. Compared with Col-0, the mutant oasa1-1 and oasa1-2 showed late leaf senescence, which may be due to disturbed cysteine homeostasis. The mutant exhibited lower total cysteine content and reduced chlorophyll degradation. Meanwhile, WRKY75 promotes cysteine production by inducing the transcription of OASA1 expression, affecting leaf senescence. Our results demonstrate that the senescence-responsive transcription factor WRKY75 directly activates the expression of OASA1 to promote cysteine accumulation and H2O2 content, suggesting a mechanism by which senescence regulates cysteine accumulation in plants.

RsWRKY75 promotes ROS scavenging and cadmium efflux via activating the transcription of RsAPX1 and RsPDR8 in radish (Raphanus sativus L.)

KEY MESSAGE

Acting as a nucleus-localized transcriptional activator, RsWRKY75 promotes ROS scavenging and Cd efflux by activating the transcription of RsAPX1 and RsPDR8 in radish. Radish (Raphanus sativus L.) is an important economical root vegetable crop worldwide. As a toxic heavy metal, cadmium (Cd) can dramatically hamper radish taproot quality as well as threaten human health. Although the WRKY transcription factors (TFs) play crucial roles in plant response to Cd stress, how WRKY TFs mediate Cd uptake and efflux remains elusive in radish. Herein, the RsWRKY75, belonging to the WRKY-IIc sub-group, displayed high expression in vascular cambium at the expanding stage, whose promoter activity and expression were obviously induced by Cd exposure at 24 h in radish root. RsWRKY75 was localized primarily to the nucleus and had transactivation activity in yeast and tobacco leaf cells. Transient transformation indicated that RsWRKY75 promoted Cd-induced ROS scavenging in radish cotyledons. Overexpression of RsWRKY75 led to increased root elongation but decreased Cd accumulation in Arabidopsis plants. Both in vitro and in vivo assays revealed that RsWRKY75 bound to the RsAPX1 promoter and activated its expression to eliminate excessive ROS accumulation. Moreover, RsWRKY75 activated RsPDR8 transcription by directly binding to its promoter, thereby promoting Cd efflux in the radish root. Collectively, we revealed a novel module of RsWRKY75-mediated ROS scavenging and Cd efflux in radish. These results would facilitate to establish genetic strategies to achieve RsWRKY75-dependent Cd extrusion and detoxification in radish.

NbNAC1 enhances plant immunity against TMV by regulating isochorismate synthase 1 expression and the SA pathway

Salicylic acid (SA) plays important roles in plant local and systemic resistance. Isochorismate synthase 1 (ICS1) is a key enzyme in SA synthesis. Pathogens infection triggered the ICS1 expression and induced SA production. However, the molecular regulation mechanism of ICS1 against virus infection remains unclear. Here, we employed molecular genetics and physiobiochemical approaches to confirm a transcription factor NbNAC1 from Nicotiana benthamiana is a positive regulator of resistance against tobacco mosaic virus (TMV). The pathways NbNAC1 and NbICS1 can be triggered by TMV infection. Silencing NbNAC1 accelerated TMV-induced oxidative damage and increased reactive oxygen species (ROS) production. It also weakened both local and systemic resistance against TMV and decreased the expression of NbICS1, SA signaling gene NbNPR1, and SA defense-related genes. The effects of NbNAC1-silencing were restored by overexpression of NbICS1 or foliar SA applications. Overexpressing NbNAC1 prevented oxidative damage and reduced the production of ROS, enhanced plant resistance against viral pathogen, and activated NbICS1 expression, and SA downstream signaling and defense-related genes. NbNAC1 localized in nuclear and emerged the ability of transcriptional regulation. ChIP and EMSA results indicated that NbNAC1 directly binds to a fragment containing GAAATT motif of NbICS1 promoter. Luciferase reporter assays confirmed that NbNAC1 activates NbICS1 expression. Taken together, our results demonstrate that NbNAC1 plays a critical role in plant immunity through activation of SA production.

Identification and functional characterization of the MYB transcription factor GmMYBLJ in soybean leaf senescence

Leaf senescence is an important agronomic trait that significantly influences the quality and yield of soybeans. v-Myb avian myeloblastosis viral oncogene homolog (MYB) transcription factors are considered crucial regulators governing leaf senescence, which can be utilized to improve agronomic traits in crops. However, our knowledge regarding the functional roles of soybean MYBs in leaf senescence is extremely limited. In this study, GmMYBLJ, a CCA1-like MYB, was identified and functionally characterized with respect to leaf senescence. The GmMYBLJ protein is localized in the nucleus, and a high accumulation of its transcripts was observed in nodules and embryos. Notably, GmMYBLJ was highly expressed in soybean senescent leaves and was transcriptionally induced by dark or NaCl treatment, as confirmed by histochemical GUS staining analysis. Ectopic overexpression of GmMYBLJ in Arabidopsis not only led to earlier leaf senescence, reduced chlorophyll content, and increased MDA accumulation but also promoted the expression of several WRKY family transcription factors and senescence-associated genes, such as SAG12 and ORE1. Further investigation showed that overexpression of GmMYBLJ accelerated Arabidopsis leaf senescence under darkness and in response to Pst DC3000 infection. Moreover, transgenic soybean plants overexpressing GmMYBLJ grew faster and exhibited accelerated senescence under salt stress. DAB staining analysis showed that GmMYBLJ induced ROS accumulation in soybean hairy roots and Arabidopsis leaves. Collectively, our results provided useful information into the functional roles of GmMYBLJ in both age-dependent and stress-induced senescence.

Consecutive oxidative stress in CATALASE2-deficient Arabidopsis negatively regulates Glycolate Oxidase1 activity through S-nitrosylation

Glycolate oxidase (GOX) is a crucial enzyme of photorespiration involving carbon metabolism and stress responses. It is poorly understood, however, how its activities are modulated in response to oxidative stress elicited by various environmental cues. Analysis of Arabidopsis catalase-defective mutant cat2 revealed that the GOX activities were gradually repressed during the growth, which were accompanied by decreased salicylic acid (SA)-dependent cell death, suggesting photorespiratory H2O2 may entrain negative feedback regulation of GOX in an age-dependent manner. Intriguingly, a loss-of-function mutation in GLYCOLATE OXIDASE1 (GOX1) rather than in GOX2 and GOX3 attenuated the SA responses of cat2. We found that GOX1 is S-nitrosylated at Cys-343 during consecutive oxidative stress in the cat2 mutant. Subsequently, increased GOX1-SNO formations may contribute to progressively decreased GOX activities and then compromised photorespiratory H2O2 flux, which forms a negative feedback loop limiting the amplified activation of SA-dependent defence responses. Together, the data reveal that GOX S-nitrosylation is involved in the crosstalk between photorespiratory H2O2 and NO signalling in the fine-tuning regulation of oxidative stress responses and further highlight that NO-based S-nitrosylation acts as an on-off switch for ROS homeostasis.

Genome-wide analysis of the NYN domain gene family in Brassica napus and its function role in plant growth and development

The NYN domain gene family consists of genes that encode ribonucleases that are characterized by a newly identified NYN domain. Members of the family were widely distributed in all life kingdoms and play a crucial role in various RNA regulation processes, although the wide genome overview of the NYN domain gene family is not yet available in any species. Rapeseed (Brassica napus L.), a polyploid model species, is an important oilseed crop. Here, the phylogenetic analysis of these BnaNYNs revealed five distinct groups strongly supported by gene structure, conserved domains, and conserved motifs. The survey of the expansion of the gene family showed that the birth of BnaNYNs is explained by various duplication events. Furthermore, tissue-specific expression analysis, protein-protein interaction prediction, and cis-element prediction suggested a role for BnaNYNs in plant growth and development. Interestingly, the data showed that three tandem duplicated BnaNYNs (TDBs) exhibited distinct expression patterns from those other BnaNYNs and had a high similarity in protein sequence level. Furthermore, the analysis of one of these TDBs, BnaNYN57, showed that overexpression of BnaNYN57 in Arabidopsis thaliana and B. napus accelerated plant growth and significantly increased silique length, while RNA interference resulted in the opposite growth pattern. It suggesting a key role for the TDBs in processes related to plant growth and development.

TRX h2-PP2AC2 module serves as a convergence node for aluminum stress and leaf senescence signals, regulating cell death via ABA-mediated ROS pathway

ROS/redox signaling plays an important role in the regulation of signal transduction and acclimation pathways activated by multiple abiotic stresses and leaf senescence. However, the regulatory events that produce ROS under different stimuli are far from clear. Here, we report the elucidation of the molecular mechanism of an h type thioredoxin, AhTRX h2, positively regulates Al sensitivity and leaf senescence by promoting ROS. AhTRX h2 transcript levels increased greatly during both natural senescence and Al stress condition in peanut. Ectopic expression of AhTRX h2 in Arabidopsis conferred Al sensitivity as well as premature leaf senescence, manifested by multiple indices, including inhibiting root elongation, severe cell death, and accelerated expression of MC1 and CEX17. AhTRX h2 exhibited similar functions to AtTRX h2, as AhTRX h2 was able to restore the phenotypes of the AtTRX h2 defective mutant (trxh2-4) which showed Al tolerant and late senescence phenotypes. The knock down of AhTRX h2 markedly suppressed Al- and senescence-induced cell death in peanut. AhTRX h2 could recruit catalytic subunit of protein phosphatase 2A (PP2AC2) to form a stable complex. The interaction between AhTRX h2 and AtPP2AC2, as well as AhPP2AC2 and AtTRX h2 was also proved. Overexpression of AhPP2AC2 significantly enhanced Al sensitivity and leaf senescence in Arabidopsis. Protein stability assay revealed that AhTRX h2 was more stable during aging or aluminum stress. Moreover, PP2AC2 could greatly enhance the stability of AhTRX h2 in vivo. Consistent with these observations, overexpression of AhPP2AC2 effectively enhanced AhTRX h2-induced Al sensitivity and precocious leaf senescence. AhTRX h2 and AhPP2AC2 required ABA and ROS in response to cell death under Al stress and senescence, and it was evidence to suggest that ABA acted upstream of ROS in this process. Together, AhTRX h2 and AhPP2AC2 constitute a stable complex that promotes the accumulation of ABA and ROS, effectively regulate cell death. These findings suggest that TRX h2-PP2AC2-mediated pathway may be a widespread mechanism in regulating Al stress and leaf senescence.

RICE LONG GRAIN 3 delays dark-induced senescence by downregulating abscisic acid signaling and upregulating reactive oxygen species scavenging activity

Leaf senescence is a complex developmental process influenced by abscisic acid (ABA) and reactive oxygen species (ROS), both of which increase during senescence. Understanding the regulatory mechanisms of leaf senescence can provide insights into enhancing crop yield and stress tolerance. In this study, we aimed to elucidate the role and mechanisms of rice (Oryza sativa) LONG GRAIN 3 (OsLG3), an APETALA2/ETHYLENE RESPONSIVE FACTOR (AP2/ERF) transcription factor, in orchestrating dark-induced leaf senescence. The transcript levels of OsLG3 gradually increased during dark-induced and natural senescence. Transgenic plants overexpressing OsLG3 exhibited delayed senescence, whereas CRISPR/Cas9-mediated oslg3 mutants exhibited accelerated leaf senescence. OsLG3 overexpression suppressed senescence-induced ABA signaling by downregulating OsABF4 (an ABA-signaling-related gene) and reduced ROS accumulation by enhancing catalase activity through upregulation of OsCATC. In vivo and in vitro binding assays demonstrated that OsLG3 downregulated OsABF4 and upregulated OsCATC by binding directly to their promoter regions. These results demonstrate the critical role of OsLG3 in fine-tuning leaf senescence progression by suppressing ABA-mediated signaling while simultaneously activating ROS-scavenging mechanisms. These findings suggest that OsLG3 could be targeted to enhance crop resilience and longevity.

Transcriptome analysis revealed that AcWRKY75 transcription factor reduced the resistance of kiwifruit to Pseudomonas syringae pv. actinidiae

The kiwifruit canker disease caused by Pseudomonas syringae pv. actinidiae (Psa) seriously threatens the development of kiwifruit industry. So far, only a limited number of Psa-resistant kiwifruit varieties have been identified, and the underlying molecular mechanisms are still largely unknown. In this study, we evaluated the Psa resistance of six hybrid populations and screened a resistant segregation population R1F2. Then, transcriptome analysis on the Psa extremely high-resistant (HR) and extremely high-susceptible (HS) plants of the R1F2 population was performed. KEGG enrichment analysis revealed that differentially expressed genes (DEGs) were significantly enriched in plant hormone signal transduction pathways, including auxin, abscisic acid, zeatin, jasmonic acid and salicylic acid. Furthermore, several transcription factors (TFs), especially WRKY TFs, were identified among the DEGs. The qRT-PCR showed that AcWRKY75 was highly expressed in the HS plants. Additionally, AcWRKY75 was significantly induced in the HS cultivar 'Hongyang' after Psa inoculation. Sequence amplification analysis showed that there was polymorphism in the DNA sequence of AcWRKY75 gene, but no HR or HS-specific differences were observed. Subcellular localization and transcriptional activity analysis confirmed that AcWRKY75 functions as a nucleus-located transcriptional activator. Transient overexpression of AcWRKY75 in kiwifruit leaves reduced the resistance to Psa, while silencing AcWRKY75 by virus-induced gene silencing (VIGS) slightly enhanced the resistance to Psa. Furthermore, AcWRKY75 exhibited a weak interaction with the promoter of the ABA-related DEG AcBet V1 (Acc27163). Our findings elucidated that AcWRKY75 may negatively regulate the Psa resistance of kiwifruit through the hormone signaling pathway, which laid a foundation for the analysis of the disease resistance mechanism of kiwifruit canker.

Evolutionary Conserved and Divergent Responses to Copper Zinc Superoxide Dismutase Inhibition in Plants

After an initial evolution in a reducing environment, life got successively challenged by reactive oxygen species (ROS), especially during the great oxidation event (GOE) that followed the development of photosynthesis. Therefore, ROS are deeply intertwined into the physiological, morphological and transcriptional responses of most present-day organisms. Copper-zinc superoxide dismutases (CuZnSODs) evolved during the GOE and are present in charophytes and extant land plants, but nearly absent from chlorophytes. The chemical inhibitor of CuZnSOD, lung cancer screen 1 (LCS-1), could greatly facilitate the study of SODs in diverse plants. Here, we determined the impact of chemical inhibition of plant CuZnSOD activity, on plant growth, transcription and metabolism. We followed a comparative approach by using different plant species, including Marchantia Polymorpha and Physcomitrium patens, representing bryophytes, the sister lineage to vascular plants, and Arabidopsis thaliana. We show that LCS-1 causes oxidative stress in plants and that the inhibition of CuZnSODs provoked a similar core response that mainly impacted glutathione homoeostasis in all plant species analysed. That said, Physcomitrium and Arabidopsis, which contain multiple CuZnSOD isoforms showed a more complex and exacerbated response. In addition, an untargeted metabolomics approach revealed a specific metabolic signature for each plant species. Our comparative analysis exposes a conserved core response at the physiological and transcriptional level towards LCS-1, while the metabolic response largely varies. These differences correlate with the number and localization of the CuZnSOD isoforms present in each species.

Hydrogen peroxide participates in leaf senescence by inhibiting CHLI1 activity

KEY MESSAGE

Hydrogen peroxide promoted leaf senescence by sulfenylating the magnesium chelating protease I subunit (CHLI1) in the chlorophyll synthesis pathway, and inhibited its activity to reduce chlorophyll synthesis. Leaf senescence is the final and crucial stage of plant growth and development, during which chlorophyll experiences varying degrees of destruction. It is well-known that the higher ROS accumulation is a key factor for leaf senescence, but whether and how ROS regulates chlorophyll synthesis in the process are unknown. Here, we report that H2O2 inhibits chlorophyll synthesis during leaf senescence via the I subunit of magnesium-chelatase (CHLI1). During leaf senescence, the decrease of chlorophyll content is accompanied by the increase of H2O2 accumulation, as well as the inhibition of catalase (CAT) genes expression. The mutant cat2-1, with increased H2O2 shows an accelerated senescence phenotype and decreased CHLI1 activity compared with the wild type. H2O2 inhibits CHLI1 activity by sulfenylating CHLI1 during leaf senescence. Consistent with this, the chli1 knockout mutant displays the same premature leaf senescence symptom as cat2-1, while overexpression of CHLI1 in cat2-1 can partially restore its early senescence phenotype. Taken together, these results illustrate that CAT2-mediated H2O2 accumulation during leaf senescence represses chlorophyll synthesis through sulfenylating CHLI1, and thus inhibits its activity, providing a new insight into the pivotal role of chlorophyll synthesis as a participant in orchestrating the leaf senescence.

Unravelling the role of WRKY transcription factors in leaf senescence: Genetic and molecular insights

BACKGROUND

Leaf senescence (LS), the final phase in leaf development, is an important and precisely regulated process crucial for plant well-being and the redistribution of nutrients. It is intricately controlled by various regulatory factors, including WRKY transcription factors (TFs). WRKYs are one of the most significant plant TF families, and several of them are differentially regulated and important during LS. Recent research has enhanced our understanding of the structural and functional characteristics of WRKY TFs, providing insights into their regulatory roles.

AIM OF REVIEW

This review aims to elucidate the genetic and molecular mechanisms underlying the intricate regulatory networks associated with LS by investigating the role of WRKY TFs. We seek to highlight the importance of WRKY-mediated signaling pathways in understanding LS, plant evolution, and response to varying environmental conditions.

KEY SCIENTIFIC CONCEPTS OF REVIEW

WRKY TFs exhibit specific DNA-binding activity at the N-terminus and dynamic interactions of the intrinsically disordered domain at the C-terminus with various proteins. These WRKY TFs not only control the activity of other WRKYs, but also interact with either WRKYs or other TFs, thereby fine- tuning the expression of target genes. By unraveling the complex interactions and regulatory mechanisms of WRKY TFs, this review broadens our knowledge of the genetic and molecular basis of LS. Understanding WRKY-mediated signalling pathways provides crucial insights into specific aspects of plant development, such as stress-induced senescence, and offers potential strategies for improving crop resilience to environmental stresses like drought and pathogen attacks. By targeting these pathways, it may be possible to enhance specific productivity traits, such as increased yield stability under adverse conditions, thereby contributing to more reliable agricultural outputs.

The BnaBPs gene regulates flowering time and leaf angle in Brassica napus

The flowering time and plant architecture of Brassica napus were significantly associated with yield. In this study, we found that the BREVIPEDICELLUS/KNAT1(BP) gene regulated the flowering time and plant architecture of B. napus. However, the precise regulatory mechanism remains unclear. We cloned two homologous BP genes, BnaBPA03 and BnaBPC03, from B. napus Xiaoyun. The protein sequence analysis showed two proteins containing conserved domains KNOX I, KNOX II, ELK, and HOX of the KONX protein family. The CRISPR/Cas9 knockout lines exhibited early budding and flowering time, coupled with floral organ abscission earlier and a larger leaf angle. On the contrary, overexpression plants displayed a phenotype that was the inverse of these characteristics. Furthermore, we observed upregulation of gibberellin and ethylene biosynthesis genes, as well as floral integrator genes in knocked-out plants. The results revealed that BnaBPs play a role in flowering time, floral organ abscission, and leaf angle as well as germination processes mediated. Additionally, BnaBPs exerted an impact on the biosynthesis pathways of ethylene and GA.

Genome-Wide Identification and Analysis of the WRKY Transcription Factor Family Associated with Leaf Senescence in Alfalfa

Leaves are the most significant parts of forage crops such as alfalfa. Senescence is the terminal stage of leaf development and is controlled by an integrated myriad of endogenous signals and environmental stimuli. WRKY transcription factors (TFs) play essential roles in regulating leaf senescence; however, only a few studies on the analysis and identification of the WRKY TF family in Medicago Sativa have been reported. In this study, we identified 198 WRKY family members from the alfalfa (M. sativa L.) cultivar 'XinjiangDaye' using phylogenetic analysis and categorized them into three subfamilies, Groups I, II, and III, based on their structural characteristics. Group II members were further divided into five subclasses. In addition, several hormone- and stress-related cis-acting elements were identified in the promoter regions of MsWRKYs. Furthermore, 14 aging-related MsWRKYs genes from a previous transcriptome in our laboratory were selected for RT-qPCR validation of their expression patterns, and subsequently cloned for overexpression examination. Finally, MsWRKY5, MsWRKY66, MsWRKY92, and MsWRKY141 were confirmed to cause leaf yellowing in Nicotiana benthaminana using a transient expression system. Our findings lay a groundwork for further studies on the mechanism of M. sativa leaf aging and for the creation of new germplasm resources.

Endoplasmic reticulum protein ALTERED MERISTEM PROGRAM 1 negatively regulates senescence in Arabidopsis

Plant senescence is a highly regulated developmental program crucial for nutrient reallocation and stress adaptation in response to developmental and environmental cues. Stress-induced and age-dependent natural senescence share both overlapping and distinct molecular responses and regulatory schemes. Previously, we have utilized a carbon-deprivation (C-deprivation) senescence assay using Arabidopsis (Arabidopsis thaliana) seedlings to investigate senescence regulation. Here we conducted a comprehensive time-resolved transcriptomic analysis of Arabidopsis wild type seedlings subjected to C-deprivation treatment at multiple time points, unveiling substantial temporal changes and distinct gene expression patterns. Moreover, we identified ALTERED MERISTEM PROGRAM 1 (AMP1), encoding an endoplasmic reticulum protein, as a potential regulator of senescence based on its expression profile. By characterizing loss-of-function alleles and overexpression lines of AMP1, we confirmed its role as a negative regulator of plant senescence. Genetic analyses further revealed a synergistic interaction between AMP1 and the autophagy pathway in regulating senescence. Additionally, we discovered a functional association between AMP1 and the endosome-localized ABNORMAL SHOOT3 (ABS3)-mediated senescence pathway and positioned key senescence-promoting transcription factors downstream of AMP1. Overall, our findings shed light on the molecular intricacies of transcriptome reprogramming during C-deprivation-induced senescence and the functional interplay among endomembrane compartments in controlling plant senescence.

Comprehensive transcriptome profiling and transcription factor identification in early/late leaf senescence grafts in potato

Potato (Solanum tuberosum L.) is recognized globally as the most significant non-cereal staple crop. Leaf senescence, which significantly impacts tuber yield, serves as a critical indicator of potato maturity. Despite its importance, the molecular mechanisms regulating this process remain largely unknown. In a previous study, we grafted the early-maturing variety 'Zhongshu 5' (Z5) onto the late-maturing variety 'Zhongshu 18' (Z18), and demonstrated that the rootstock's leaves displayed physiological characteristics suggestive of early senescence. Here, we analyzed the transcriptome data of the Z5 and Z18 grafts to conduct weighted gene co-expression network and gene expression clustering analysis. Differentially expressed genes in cluster 9, as well as the floralwhite module, exhibited markedly elevated expression levels during the onset of leaf senescence. These genes were found to be enriched in several senescence related processes, such as chloroplast organization, electron transport chain, and chlorophyll metabolic process. Furthermore, we constructed transcription factor correlation networks and hub gene co-expression networks. By monitoring the expression patterns of these genes throughout the whole growth period, we identified two candidate genes, StWRKY70 and StNAP, which may play pivotal roles in leaf senescence. This study contributes valuable genetic resources for further investigations into the regulatory mechanism governing potato leaf senescence, with implications for genetic improvements, particularly in terms of maturity and yield.

Regulatory networks of senescence-associated gene-transcription factors promote degradation in Moso bamboo shoots

Bamboo cultivation, particularly Moso bamboo (Phyllostachys edulis), holds significant economic importance in various regions worldwide. Bamboo shoot degradation (BSD) severely affects productivity and economic viability. However, despite its agricultural consequences, the molecular mechanisms underlying BSD remain unclear. Consequently, we explored the dynamic changes of BSD through anatomy, physiology and the transcriptome. Our findings reveal ruptured protoxylem cells, reduced cell wall thickness and the accumulation of sucrose and reactive oxygen species (ROS) during BSD. Transcriptomic analysis underscored the importance of genes related to plant hormone signal transduction, sugar metabolism and ROS homoeostasis in this process. Furthermore, BSD appears to be driven by the coexpression regulatory network of senescence-associated gene transcription factors (SAG-TFs), specifically PeSAG39, PeWRKY22 and PeWRKY75, primarily located in the protoxylem of vascular bundles. Yeast one-hybrid and dual-luciferase assays demonstrated that PeWRKY22 and PeWRKY75 activate PeSAG39 expression by binding to its promoter. This study advanced our understanding of the molecular regulatory mechanisms governing BSD, offering a valuable reference for enhancing Moso bamboo forest productivity.

Clathrin light chains negatively regulate plant immunity by hijacking the autophagy pathway

The crosstalk between clathrin-mediated endocytosis (CME) and the autophagy pathway has been reported in mammals; however, the interconnection of CME with autophagy has not been established in plants. Here, we report that the Arabidopsis CLATHRIN LIGHT CHAIN (CLC) subunit 2 and 3 double mutant, clc2-1 clc3-1, phenocopies Arabidopsis AUTOPHAGY-RELATED GENE (ATG) mutants in both autoimmunity and nutrient sensitivity. Accordingly, the autophagy pathway is significantly compromised in the clc2-1 clc3-1 mutant. Interestingly, multiple assays demonstrate that CLC2 directly interacts with ATG8h/ATG8i in a domain-specific manner. As expected, both GFP-ATG8h/GFP-ATG8i and CLC2-GFP are subjected to autophagic degradation, and degradation of GFP-ATG8h is significantly reduced in the clc2-1 clc3-1 mutant. Notably, simultaneous knockout of ATG8h and ATG8i by CRISPR-Cas9 results in enhanced resistance against Golovinomyces cichoracearum, supporting the functional relevance of the CLC2-ATG8h/8i interactions. In conclusion, our results reveal a link between the function of CLCs and the autophagy pathway in Arabidopsis.

Arabidopsis WRKY1 promotes monocarpic senescence by integrative regulation of flowering, leaf senescence, and nitrogen remobilization

Monocarpic senescence, characterized by whole-plant senescence following a single flowering phase, is widespread in seed plants, particularly in crops, determining seed harvest time and quality. However, how external and internal signals are systemically integrated into monocarpic senescence remains largely unknown. Here, we report that the Arabidopsis thaliana transcription factor WRKY1 plays essential roles in multiple key steps of monocarpic senescence. WRKY1 expression is induced by age, salicylic acid (SA), and nitrogen (N) deficiency. Flowering and leaf senescence are accelerated in the WRKY1 overexpression lines but are delayed in the wrky1 mutants. The combined DNA affinity purification sequencing and RNA sequencing analyses uncover the direct target genes of WRKY1. Further studies show that WRKY1 coordinately regulates three processes in monocarpic senescence: (1) suppressing FLOWERING LOCUS C gene expression to initiate flowering, (2) inducing SA biosynthesis genes to promote leaf senescence, and (3) activating the N assimilation and transport genes to trigger N remobilization. In summary, our study reveals how one stress-responsive transcription factor, WRKY1, integrates flowering, leaf senescence, and N remobilization processes into monocarpic senescence, providing important insights into plant lifetime regulation.

WRKY47 transcription factor modulates leaf senescence through regulating PCD-associated genes in Arabidopsis

Transcription factors play crucial roles in almost all physiological processes including leaf senescence. Cell death is a typical symptom appearing in senescing leaves, which is also classified as developmental programmed cell death (PCD). However, the link between PCD and leaf senescence still remains unclear. Here, we found a WRKY transcription factor WRKY47 positively modulates age-dependent leaf senescence in Arabidopsis (Arabidopsis thaliana). WRKY47 was expressed preferentially in senescing leaves. A subcellular localization assay indicated that WRKY47 was exclusively localized in nuclei. Overexpression of WRKY47 showed precocious leaf senescence, with less chlorophyll content and higher electrolyte leakage, but loss-of-function mutants of WRKY47 delayed this biological process. Through qRT-PCR and dual luciferase reporter assays, we found that WRKY47 could activate the expression of senescence-associated genes (SAGs) and PCD-associated genes to regulate leaf senescence. Furthermore, through electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP)-qPCR, WRKY47 was found to bind to W-box fragments in promoter regions of BFN1 (Bifunctional Nuclease 1) and MC6 (Metacaspase 6) directly. In general, our research revealed that WRKY47 regulates age-dependent leaf senescence by activating the transcription of two PCD-associated genes.

Genome-wide expression analysis of vegetative organs during developmental and herbicide-induced whole plant senescence in Arabidopsis thaliana

BACKGROUND

Whole plant senescence represents the final stage in the life cycle of annual plants, characterized by the decomposition of aging organs and transfer of nutrients to seeds, thereby ensuring the survival of next generation. However, the transcriptomic profile of vegetative organs during this death process remains to be fully elucidated, especially regarding the distinctions between natural programmed death and artificial sudden death induced by herbicide.

RESULTS

Differential genes expression analysis using RNA-seq in leaves and roots of Arabidopsis thaliana revealed that natural senescence commenced in leaves at 45-52 days after planting, followed by roots initiated at 52-60 days. Additionally, both organs exhibited similarities with artificially induced senescence by glyphosate. Transcription factors Rap2.6L and WKRY75 appeared to serve as central mediators of regulatory changes during natural senescence, as indicated by co-expression networks. Furthermore, the upregulation of RRTF1, exclusively observed during natural death, suggested its role as a regulator of jasmonic acid and reactive oxygen species (ROS) responses, potentially triggering nitrogen recycling in leaves, such as the glutamate dehydrogenase (GDH) shunt. Root senescence was characterized by the activation of AMT2;1 and GLN1;3, facilitating ammonium availability for root-to-shoot translocation, likely under the regulation of PDF2.1.

CONCLUSIONS

Our study offers valuable insights into the transcriptomic interplay between phytohormones and ROS during whole plant senescence. We observed distinct regulatory networks governing nitrogen utilization in leaf and root senescence processes. Furthermore, the efficient allocation of energy from vegetative organs to seeds emerges as a critical determinant of population sustainability of annual Arabidopsis.

Pepper immunity against Ralstonia solanacearum is positively regulated by CaWRKY3 through modulation of different WRKY transcription factors

BACKGROUND

Several WRKY transcription factors (TFs), including CaWRKY6, CaWRKY22, CaWRKY27, and CaWRKY40 are known to govern the resistance of pepper (Capsicum annuum L.) plants to Ralstonia solanacearum infestation (RSI) and other abiotic stresses. However, the molecular mechanisms underlying these processes remain elusive.

METHODS

This study functionally described CaWRKY3 for its role in pepper immunity against RSI. The roles of phytohormones in mediating the expression levels of CaWRKY3 were investigated by subjecting pepper plants to 1 mM salicylic acid (SA), 100 µM methyl jasmonate (MeJA), and 100 µM ethylene (ETH) at 4-leaf stage. A virus-induced gene silencing (VIGS) approach based on the Tobacco Rattle Virus (TRV) was used to silence CaWRKY3 in pepper, and transiently over-expressed to infer its role against RSI.

RESULTS

Phytohormones and RSI increased CaWRKY3 transcription. The transcriptions of defense-associated marker genes, including CaNPR1, CaPR1, CaDEF1, and CaHIR1 were decreased in VIGS experiment, which made pepper less resistant to RSI. Significant hypersensitive (HR)-like cell death, H2O2 buildup, and transcriptional up-regulation of immunological marker genes were noticed in pepper when CaWRKY3 was transiently overexpressed. Transcriptional activity of CaWRKY3 was increased with overexpression of CaWRKY6, CaWRKY22, CaWRKY27, and CaWRKY40, and vice versa. In contrast, Pseudomonas syringae pv tomato DC3000 (Pst DC3000) was easily repelled by the innate immune system of transgenic Arabidopsis thaliana that overexpressed CaWRKY3. The transcriptions of defense-related marker genes like AtPR1, AtPR2, and AtNPR1 were increased in CaWRKY3-overexpressing transgenic A. thaliana plants.

CONCLUSION

It is concluded that CaWRKY3 favorably regulates phytohormone-mediated synergistic signaling, which controls cell death in plant and immunity of pepper plant against bacterial infections.

Expression and function identification of senescence-associated genes under continuous drought treatment in grapevine (Vitis vinifera L.) leaves

Natural leaf senescence is critical for plant fitness. Drought-induced premature leaf senescence affects grape yield and quality. However, reports on the regulatory mechanisms underlying premature leaf senescence under drought stress are limited. In this study, two-year-old potted 'Muscat Hamburg' grape plants were subjected to continuous natural drought treatment until mature leaves exhibited senescence symptoms. Physiological and biochemical indices related to drought stress and senescence were monitored. Transcriptome and transgenic Arabidopsis were used to perform expression analyses and functional identification of drought-induced senescence-associated genes. Twelve days of continuous drought stress was sufficient to cause various physiological disruptions and visible senescence symptoms in mature 'Muscat Hamburg' leaves. These disruptions included malondialdehyde and H2O2 accumulation, and decreased catalase activity and chlorophyll (Chl) levels. Transcriptome analysis revealed that most genes involved in photosynthesis and Chl synthesis were downregulated after 12 d of drought treatment. Three key Chl catabolic genes (SGR, NYC1, and PAO) were significantly upregulated. Overexpression of VvSGR in wild Arabidopsis further confirmed that SGR directly promoted early yellowing of cotyledons and leaves. In addition, drought treatment decreased expression of gibberellic acid signaling repressors (GAI and GAI1) and cytokinin signal components (AHK4, AHK2, RR22, RR9-1, RR9-2, RR6, and RR4) but significantly increased the expression of abscisic acid, jasmonic acid, and salicylic acid signaling components and responsive transcription factors (bZIP40/ABF2, WRKY54/75/70, ANAC019, and MYC2). Moreover, some NAC members (NAC0002, NAC019, and NAC048) may also be drought-induced senescence-associated genes. These results provide extensive information on candidate genes involved in drought-induced senescence in grape leaves.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-024-01465-2.

Sequential activation of strigolactone and salicylate biosynthesis promotes leaf senescence

Leaf senescence is a complex process strictly regulated by various external and endogenous factors. However, the key signaling pathway mediating leaf senescence remains unknown. Here, we show that Arabidopsis SPX1/2 negatively regulate leaf senescence genetically downstream of the strigolactone (SL) pathway. We demonstrate that the SL receptor AtD14 and MAX2 mediate the age-dependent degradation of SPX1/2. Intriguingly, we uncover an age-dependent accumulation of SLs in leaves via transcriptional activation of SL biosynthetic genes by the transcription factors (TFs) SPL9/15. Furthermore, we reveal that SPX1/2 interact with the WRKY75 subclade TFs to inhibit their DNA-binding ability and thus repress transcriptional activation of salicylic acid (SA) biosynthetic gene SA Induction-Deficient 2, gating the age-dependent SA accumulation in leaves at the leaf senescence onset stage. Collectively, our new findings reveal a signaling pathway mediating sequential activation of SL and salicylate biosynthesis for the onset of leaf senescence in Arabidopsis.

AtVQ25 promotes salicylic acid-related leaf senescence by fine-tuning the self-repression of AtWRKY53

Most mechanistic details of chronologically ordered regulation of leaf senescence are unknown. Regulatory networks centered on AtWRKY53 are crucial for orchestrating and integrating various senescence-related signals. Notably, AtWRKY53 binds to its own promoter and represses transcription of AtWRKY53, but the biological significance and mechanism underlying this self-repression remain unclear. In this study, we identified the VQ motif-containing protein AtVQ25 as a cooperator of AtWRKY53. The expression level of AtVQ25 peaked at mature stage and was specifically repressed after the onset of leaf senescence. AtVQ25-overexpressing plants and atvq25 mutants displayed precocious and delayed leaf senescence, respectively. Importantly, we identified AtWRKY53 as an interacting partner of AtVQ25. We determined that interaction between AtVQ25 and AtWRKY53 prevented AtWRKY53 from binding to W-box elements on the AtWRKY53 promoter and thus counteracted the self-repression of AtWRKY53. In addition, our RNA-sequencing data revealed that the AtVQ25-AtWRKY53 module is related to the salicylic acid (SA) pathway. Precocious leaf senescence and SA-induced leaf senescence in AtVQ25-overexpressing lines were inhibited by an SA pathway mutant, atsid2, and NahG transgenic plants; AtVQ25-overexpressing/atwrky53 plants were also insensitive to SA-induced leaf senescence. Collectively, we demonstrated that AtVQ25 directly attenuates the self-repression of AtWRKY53 during the onset of leaf senescence, which is substantially helpful for understanding the timing of leaf senescence onset modulated by AtWRKY53.

Multi-omics analyses of sid2 mutant reflect the need of isochorismate synthase ICS1 to cope with sulfur limitation in Arabidopsis thaliana

The SID2 (SA INDUCTION-DEFICIENT2) gene that encodes ICS1 (isochorismate synthase), plays a central role in salicylic acid biosynthesis in Arabidopsis. The sid2 and NahG (encoding a bacterial SA hydroxylase) overexpressing mutants (NahG-OE) have currently been shown to outperform wild type, presenting delayed leaf senescence, higher plant biomass and better seed yield. When grown under sulfate-limited conditions (low-S), sid2 mutants exhibited early leaf yellowing compared to the NahG-OE, the npr1 mutant affected in SA signaling pathway, and WT. This indicated that the hypersensitivity of sid2 to sulfate limitation was independent of the canonical npr1 SA-signaling pathway. Transcriptomic and proteomic analyses revealed that major changes occurred in sid2 when cultivated under low-S, changes that were in good accordance with early senescence phenotype and showed the exacerbation of stress responses. The sid2 mutants displayed a lower sulfate uptake capacity when cultivated under low-S and lower S concentrations in their rosettes. Higher glutathione concentrations in sid2 rosettes under low-S were in good accordance with the higher abundance of proteins involved in glutathione and ascorbate redox metabolism. Amino acid and lipid metabolisms were also strongly modified in sid2 under low-S. Depletion of total fatty acids in sid2 under low-S was consistent with the fact that S-metabolism plays a central role in lipid synthesis. Altogether, our results show that functional ICS1 is important for plants to cope with S limiting conditions.

Temporal Transcriptome Profiling of Pinus densiflora Infected with Pine Wood Nematode Reveals Genetically Programmed Changes upon Pine Wilt Disease

Pine, an evergreen conifer, is widely distributed worldwide. It is economically, scientifically, and ecologically important. However, pine wilt disease (PWD) induced by the pine wood nematode (PWN) adversely affects pine trees. Many studies have been conducted on the PWN and its beetle vectors to prevent the spread of PWD. However, studies providing a comprehensive understanding of the pine tree transcriptome in response to PWN infection are lacking. Here, we performed temporal profiling of the pine tree transcriptome using PWD-infected red pine trees, Pinus densiflora, inoculated with the PWN by RNA sequencing. Our analysis revealed that defense-responsive genes involved in cell wall modification, jasmonic acid signaling, and phenylpropanoid-related processes were significantly enriched 2 weeks after PWD infection. Furthermore, some WRKY-type and MYB-type transcription factors were upregulated 2 weeks after PWD infection, suggesting that these transcription factors might be responsible for the genome-wide reprogramming of defense-responsive genes in the early PWD stage. Our comprehensive transcriptome analysis will assist in developing PWD-resistant pine trees and identifying genes to diagnose PWD at the early stage of infection, during which large-scale phenotypic changes are absent in PWD-infected pine trees.

Transcriptomic and metabolomic profiling provide insight into the role of sugars and hormones in leaf senescence of Pinellia ternata

KEY MESSAGE

The interaction network and pathway map uncover the potential crosstalk between sugar and hormone metabolisms as a possible reason for leaf senescence in P. ternata. Pinellia ternata, an environmentally sensitive medicinal plant, undergoes leaf senescence twice a year, affecting its development and yield. Understanding the potential mechanism that delays leaf senescence could theoretically decrease yield losses. In this study, a typical senescent population model was constructed, and an integrated analysis of transcriptomic and metabolomic profiles of P. ternata was conducted using two early leaf senescence populations and two stay-green populations. The result showed that two key gene modules were associated with leaf senescence which were mainly enriched in sugar and hormone signaling pathways, respectively. A network constructed by unigenes and metabolisms related to the obtained two pathways revealed that several compounds such as D-arabitol and 2MeScZR have a higher significance ranking. In addition, a total of 130 hub genes in this network were categorized into 3 classes based on connectivity. Among them, 34 hub genes were further analyzed through a pathway map, the potential crosstalk between sugar and hormone metabolisms might be an underlying reason of leaf senescence in P. ternata. These findings address the knowledge gap regarding leaf senescence in P. ternata, providing candidate germplasms for molecular breeding and laying theoretical basis for the realization of finely regulated cultivation in future.

Tulip transcription factor TgWRKY75 activates salicylic acid and abscisic acid biosynthesis to synergistically promote petal senescence

WRKY transcription factors play a central role in controlling plant organ senescence; however, it is unclear whether and how they regulate petal senescence in the widely grown ornamental plant tulip (Tulipa gesneriana). In this study, we report that TgWRKY75 promotes petal senescence by enhancing the synthesis of both abscisic acid (ABA) and salicylic acid (SA) in tulip and in transgenic Arabidopsis. The expression level of TgWRKY75 was up-regulated in senescent petals, and exogenous ABA or SA treatment induced its expression. The endogenous contents of ABA and SA significantly increased during petal senescence and in response to TgWRKY75 overexpression. Two SA synthesis-related genes, TgICS1 and TgPAL1, were identified as direct targets of TgWRKY75, which binds to their promoters. In parallel, TgWRKY75 activated the expression of the ABA biosynthesis-related gene TgNCED3 via directly binding to its promoter region. Site mutation of the W-box core motif located in the promoters of TgICS1, TgPAL1, and TgNCED3 eliminated their interactions with TgWRKY75. In summary, our study demonstrates a dual regulation of ABA and SA biosynthesis by TgWRKY75, revealing a synergistic process of tulip petal senescence through feedback regulation between TgWRKY75 and the accumulation of ABA and SA.

Genome-Wide Analysis of the WRKY Transcription Factor Family in Roses and Their Putative Role in Defence Signalling in the Rose-Blackspot Interaction

WRKY transcription factors are important players in plant regulatory networks, where they control and integrate various physiological processes and responses to biotic and abiotic stresses. Here, we analysed six rose genomes of 5 different species (Rosa chinensis, R. multiflora, R. roxburghii, R. sterilis, and R. rugosa) and extracted a set of 68 putative WRKY genes, extending a previously published set of 58 WRKY sequences based on the R. chinensis genome. Analysis of the promoter regions revealed numerous motifs related to induction by abiotic and, in some cases, biotic stressors. Transcriptomic data from leaves of two rose genotypes inoculated with the hemibiotrophic rose black spot fungus Diplocarpon rosae revealed the upregulation of 18 and downregulation of 9 of these WRKY genes after contact with the fungus. Notably, the resistant genotype exhibited the regulation of 25 of these genes (16 upregulated and 9 downregulated), while the susceptible genotype exhibited the regulation of 20 genes (15 upregulated and 5 downregulated). A detailed RT-qPCR analysis of RcWRKY37, an orthologue of AtWRKY75 and FaWRKY1, revealed induction patterns similar to those of the pathogenesis-related (PR) genes induced in salicylic acid (SA)-dependent defence pathways in black spot inoculation experiments. However, the overexpression of RcWRKY37 in rose petals did not induce the expression of any of the PR genes upon contact with black spot. However, wounding significantly induced the expression of RcWRKY37, while heat, cold, or drought did not have a significant effect. This study provides the first evidence for the role of RcWRKY37 in rose signalling cascades and highlights the differences between RcWRKY37 and AtWRKY75. These results improve our understanding of the regulatory function of WRKY transcription factors in plant responses to stress factors. Additionally, they provide foundational data for further studies.

Melatonin - This is important to know

MEL (N-acetyl-5-methoxytryptamine) is a well-known natural compound that controls cellular processes in both plants and animals and is primarily found in plants as a neurohormone. Its roles have been described very broadly, from its antioxidant function related to the photoperiod and determination of seasonal rhythms to its role as a signalling molecule, imitating the action of plant hormones (or even being classified as a prohormone). MEL positively affects the yield and survival of plants by increasing their tolerance to unfavourable biotic and abiotic conditions, which makes MEL widely applicable in ecological farming as a stimulant of growth and development. Thus, it is called a phytobiostimulator. In this review, we discuss the genesis of MEL functions, the presence of MEL at the cellular level and its effects on gene expression and plant development, which can ensure the survival of plants under the conditions they encounter. Moreover, we consider the future application possibilities of MEL in agriculture.

Tobacco Transcription Factor NtWRKY70b Facilitates Leaf Senescence via Inducing ROS Accumulation and Impairing Hydrogen Sulfide Biosynthesis

Leaf senescence is the terminal stage of leaf development, and its initiation and progression are closely controlled by the integration of a myriad of endogenous signals and environmental stimuli. It has been documented that WRKY transcription factors (TFs) play essential roles in regulating leaf senescence, yet the molecular mechanism of WRKY-mediated leaf senescence still lacks detailed elucidation in crop plants. In this study, we cloned and identified a tobacco WRKY TF gene, designated NtWRKY70b, acting as a positive regulator of natural leaf senescence. The expression profile analysis showed that NtWRKY70b transcript levels were induced by aging and hydrogen peroxide (H2O2) and downregulated upon hydrogen sulfide (H2S) treatment. The physiological and biochemical assays revealed that overexpression of NtWRKY70b (OE) clearly promoted leaf senescence, triggering increased levels of reactive oxygen species (ROS) and decreased H2S content, while disruption of NtWRKY70b by chimeric repressor silencing technology (SRDX) significantly delayed the onset of leaf senescence, leading to a decreased accumulation of ROS and elevated concentration of H2S. The quantitative real-time PCR analysis showed that the expression levels of various senescence-associated genes and ROS biosynthesis-related genes (NtRbohD and NtRbohE) were upregulated in OE lines, while the expression of H2S biosynthesis-related genes (NtDCD and NtCYSC1) were inhibited in OE lines. Furthermore, the Yeast one-hybrid analysis (Y1H) and dual luciferase assays showed that NtWRKY70b could directly upregulate the expression of an ROS biosynthesis-related gene (NtRbohD) and a chlorophyll degradation-related gene (NtPPH) by binding to their promoter sequences. Accordingly, these results indicated that NtWYKY70b directly activated the transcript levels of NtRbohD and NtPPH and repressed the expression of NtDCD and NtCYCS1, thereby promoting ROS accumulation and impairing the endogenous H2S production, and subsequently accelerating leaf aging. These observations improve our knowledge of the regulatory mechanisms of WRKY TFs controlling leaf senescence and provide a novel method for ensuring high agricultural crop productivity via genetic manipulation of leaf senescence in crops.

KAKU4 regulates leaf senescence through modulation of H3K27me3 deposition in the Arabidopsis genome

Lamins are the major components of the nuclear lamina, which regulate chromatin structure and gene expression. KAKU4 is a unique nuclear lamina component in the nuclear periphery, modulates nuclear shape and size in Arabidopsis. The knowledge about the regulatory role of KAKU4 in leaf development remains limited. Here we found that knockdown of KAKU4 resulted in an accelerated leaf senescence phenotype, with elevated levels of H2O2 and hormones, particularly SA, JA, and ABA. Our results demonstrated the importance of KAKU4 as a potential negative regulator in age-triggered leaf senescence in Arabidopsis. Furthermore, we conducted combination analyses of transcriptomic and epigenomic data for the kaku4 mutant and WT leaves. The knockdown of KAKU4 lowered H3K27me3 deposition in the up-regulated genes associated with hormone pathways, programmed cell death, and leaf senescence, including SARD1, SAG113/HAI1, PR2, and so forth. In addition, we found the functional crosstalks between KAKU4 and its associated proteins (CRWN1/4, PNET2, GBPL3, etc.) through comparing multiple transcriptome datasets. Overall, our results indicated that KAKU4 may inhibit the expression of a series of genes related to hormone signals and H2O2 metabolism by affecting the deposition of H3K27me3, thereby suppressing leaf senescence.

Flavin-containing monooxygenases FMOGS-OXs integrate flowering transition and salt tolerance in Arabidopsis thaliana

Salt stress substantially leads to flowering delay. The regulation of salt-induced late flowering has been studied at the transcriptional and protein levels; however, the involvement of secondary metabolites has rarely been investigated. Here, we report that FMOGS-OXs (EC 1.14.13.237), the enzymes that catalyze the biosynthesis of glucosinolates (GSLs), promote flowering transition in Arabidopsis thaliana. It has been reported that WRKY75 is a positive regulator, and MAF4 is a negative regulator of flowering transition. The products of FMOGS-OXs, methylsulfinylalkyl GSLs (MS GSLs), facilitate flowering by inducing WRKY75 and repressing the MAS-MAF4 module. We further show that the degradation of MS GSLs is involved in salt-induced late flowering and salt tolerance. Salt stress induces the expression of myrosinase genes, resulting in the degradation of MS GSLs, thereby relieving the promotion of WRKY75 and inhibition of MAF4, leading to delayed flowering. In addition, the degradation products derived from MS GSLs enhance salt tolerance. Previous studies have revealed that FMOGS-OXs exhibit alternative catalytic activity to form trimethylamine N-oxide (TMAO) under salt stress, which activates multiple stress-related genes to promote salt tolerance. Therefore, FMOGS-OXs integrate flowering transition and salt tolerance in various ways. Our study shed light on the functional diversity of GSLs and established a connection between flowering transition, salt resistance, and GSL metabolism.

Transcriptional dynamics in source-sink tissues identifies molecular factors regulating the corm development process in saffron (Crocus sativus L.)

AIMS

Geophytic plants have evolved to develop underground storage organs (USO) in the active growing season to withstand harsh environments as well as to coordinate growth and reproduction when conditions are favourable. Saffron is an autumn flowering geophyte and an expensive spice crop restricted to certain geographical locations in the world. Saffron, being sterile, does not produce seeds and thus propagates only through corms, the quality of which determines its yield. Corm development in saffron is unexplored and the underlying molecular mechanism is still elusive. In this study, we performed an extensive characterisation of the transcriptional dynamics in the source (leaf) and sink (corm) tissues during corm development in saffron.

KEY RESULTS

Via morphological and transcriptome studies, we identified molecular factors regulating corm development process in saffron, which defined corm development into three stages: the initiation stage demonstrates enhanced vegetative growth aboveground and swelling of shoot base belowground due to active cell division & carbohydrate storage; the bulking stage comprises of increased source and sink strength, active photosynthesis, circadian gating and starch accumulation; the maturation stage represents reduced source and sink strength, lowered photosynthesis, sugar transport, starch synthesis and cell cycle arrest.

UTILITY

The global view of transcriptional changes in source and sink identifies similar and new molecular factors involved in the saffron corm development process compared to USO formation in other geophytes and provides a valuable resource for dissecting the molecular network underlying the corm development. We propose a hypothetical model based on data analysis, of how molecular factors via environmental cues can regulate the corm development process in saffron.

PHR1 involved in the regulation of low phosphate-induced leaf senescence by modulating phosphorus homeostasis in Arabidopsis

Phosphorus (P) is a crucial macronutrient for plant growth, development, and reproduction. The effects of low P (LP) stress on leaf senescence and the role of PHR1 in LP-induced leaf senescence are still unknown. Here, we report that PHR1 plays a crucial role in LP-induced leaf senescence, showing delayed leaf senescence in phr1 mutant and accelerated leaf senescence in 35S:PHR1 transgenic Arabidopsis under LP stress. The transcriptional profiles indicate that 763 differentially expressed SAGs (DE-SAGs) were upregulated and 134 DE-SAGs were downregulated by LP stress. Of the 405 DE-SAGs regulated by PHR1, 27 DE-SAGs were involved in P metabolism and transport. PHR1 could bind to the promoters of six DE-SAGs (RNS1, PAP17, SAG113, NPC5, PLDζ2, and Pht1;5), and modulate them in LP-induced senescing leaves. The analysis of RNA content, phospholipase activity, acid phosphatase activity, total P and phosphate content also revealed that PHR1 promotes P liberation from senescing leaves and transport to young tissues under LP stress. Our results indicated that PHR1 is one of the crucial modulators for P recycling and redistribution under LP stress, and the drastic decline of P level is at least one of the causes of early senescence in P-deficient leaves.

The WRKY46-MYC2 module plays a critical role in E-2-hexenal-induced anti-herbivore responses by promoting flavonoid accumulation

Volatile organic compounds (VOCs) play key roles in plant-plant communication, especially in response to pest attack. E-2-hexenal is an important component of VOCs, but it is unclear whether it can induce endogenous plant resistance to insects. Here, we show that E-2-hexenal activates early signaling events in Arabidopsis (Arabidopsis thaliana) mesophyll cells, including an H2O2 burst at the plasma membrane, the directed flow of calcium ions, and an increase in cytosolic calcium concentration. Treatment of wild-type Arabidopsis plants with E-2-hexenal increases their resistance when challenged with the diamondback moth Plutella xylostella L., and this phenomenon is largely lost in the wrky46 mutant. Mechanistically, E-2-hexenal induces the expression of WRKY46 and MYC2, and the physical interaction of their encoded proteins was verified by yeast two-hybrid, firefly luciferase complementation imaging, and in vitro pull-down assays. The WRKY46-MYC2 complex directly binds to the promoter of RBOHD to promote its expression, as demonstrated by luciferase reporter, yeast one-hybrid, chromatin immunoprecipitation, and electrophoretic mobility shift assays. This module also positively regulates the expression of E-2-hexenal-induced naringenin biosynthesis genes (TT4 and CHIL) and the accumulation of total flavonoids, thereby modulating plant tolerance to insects. Together, our results highlight an important role for the WRKY46-MYC2 module in the E-2-hexenal-induced defense response of Arabidopsis, providing new insights into the mechanisms by which VOCs trigger plant defense responses.

Hydrogen Peroxide Promotes Tomato Leaf Senescence by Regulating Antioxidant System and Hydrogen Sulfide Metabolism

Hydrogen peroxide (H2O2) is relatively stable among ROS (reactive oxygen species) and could act as a signal in plant cells. In the present work, detached tomato leaves were treated with exogenous H2O2 at 10 mmol/L for 8 h to study the mechanism of how H2O2 regulates leaf senescence. The data indicated that H2O2 treatment significantly accelerated the degradation of chlorophyll and led to the upregulation of the expression of leaf senescence-related genes (NYC1, PAO, PPH, SGR1, SAG12 and SAG15) during leaf senescence. H2O2 treatment also induced the accumulation of H2O2 and malondialdehyde (MDA), decreased POD and SOD enzyme activities and inhibited H2S production by reducing the expression of LCD1/2 and DCD1/2. A correlation analysis indicated that H2O2 was significantly and negatively correlated with chlorophyll, the expression of leaf senescence-related genes, and LCD1/2 and DCD1/2. The principal component analysis (PCA) results show that H2S showed the highest load value followed by O2•-, H2O2, DCD1, SAG15, etc. Therefore, these findings provide a basis for studying the role of H2O2 in regulating detached tomato leaf senescence and demonstrated that H2O2 plays a positive role in the senescence of detached leaves by repressing antioxidant enzymes and H2S production.

The mechanism of low blue light-induced leaf senescence mediated by GmCRY1s in soybean

Leaf senescence is a crucial trait that has a significant impact on crop quality and yield. Previous studies have demonstrated that light is a key factor in modulating the senescence process. However, the precise mechanism by which plants sense light and control senescence remains largely unknown, particularly in crop species. In this study, we reveal that the reduction in blue light under shading conditions can efficiently induce leaf senescence in soybean. The blue light receptors GmCRY1s rather than GmCRY2s, primarily regulate leaf senescence in response to blue light signals. Our results show that GmCRY1s interact with DELLA proteins under light-activated conditions, stabilizing them and consequently suppressing the transcription of GmWRKY100 to delay senescence. Conversely, LBL reduces the interaction between GmCRY1s and the DELLA proteins, leading to their degradation and premature senescence of leaves. Our findings suggest a GmCRY1s-GmDELLAs-GmWRKY100 regulatory cascade that is involved in mediating LBL-induced leaf senescence in soybean, providing insight into the mechanism of how light signals regulate leaf senescence. Additionally, we generate GmWRKY100 knockout soybeans that show delayed leaf senescence and improved yield under natural field conditions, indicating potential applications in enhancing soybean production by manipulating the leaf senescence trait.

The Mining of Genetic Loci and the Analysis of Candidate Genes to Identify the Physical and Chemical Markers of Anti-Senescence in Rice

Premature senescence is a common occurrence in rice production, and seriously affects rice plants' nutrient utilization and growth. A total of 120 recombinant inbred lines (RILs) were obtained from successive self-crossing of F12 generations derived from Huazhan and Nekken2. The superoxide dismutase (SOD) activity, malondialdehyde (MDA), content and catalase (CAT) activity related to the anti-senescence traits and enzyme activity index of rice were measured for QTL mapping using 4858 SNPs. Thirteen QTLs related to anti-senescence were found, among which the highest LOD score was 5.70. Eighteen anti-senescence-related genes were found in these regions, and ten of them differed significantly between the parents. It was inferred that LOC_Os01g61500, LOC_Os01g61810, and LOC_Os04g40130 became involved in the regulation of the anti-senescence molecular network upon upregulation of their expression levels. The identified anti-senescence-related QTLs and candidate genes provide a genetic basis for further research on the mechanism of the molecular network that regulates premature senescence.

Spliceosomal protein U2B″ delays leaf senescence by enhancing splicing variant JAZ9β expression to attenuate jasmonate signaling in Arabidopsis

The regulatory framework of leaf senescence is gradually becoming clearer; however, the fine regulation of this process remains largely unknown. Here, genetic analysis revealed that U2 small nuclear ribonucleoprotein B (U2B″), a component of the spliceosome, is a negative regulator of leaf senescence. Mutation of U2B″ led to precocious leaf senescence, whereas overexpression of U2B″ extended leaf longevity. Transcriptome analysis revealed that the jasmonic acid (JA) signaling pathway was activated in the u2b″ mutant. U2B″ enhances the generation of splicing variant JASMONATE ZIM-DOMAIN 9β (JAZ9β) with an intron retention in the Jas motif, which compromises its interaction with CORONATINE INSENSITIVE1 and thus enhances the stability of JAZ9β protein. Moreover, JAZ9β could interact with MYC2 and obstruct its activity, thereby attenuating JA signaling. Correspondingly, overexpression of JAZ9β rescued the early senescence phenotype of the u2b″ mutant. Furthermore, JA treatment promoted expression of U2B″ that was found to be a direct target of MYC2. Overexpression of MYC2 in the u2b″ mutant resulted in a more pronounced premature senescence than that in wild-type plants. Collectively, our findings reveal that the spliceosomal protein U2B″ fine-tunes leaf senescence by enhancing the expression of JAZ9β and thereby attenuating JA signaling.

WRKY transcription factors in Arachis hypogaea and its donors: From identification to function prediction

WRKY transcription factors (TFs) play important roles in plant growth and development and responses to abiotic and biotic stresses. Since the initial isolation of a WRKY TF in Ipomoea batatas in 1994, WRKY TFs have been identified in plants, protozoa, and fungi. Peanut (Arachis hypogaea) is a key oil and protein crop for humans and a forage source for animal consumption. Several Arachis genomes have been sequenced and genome-wide WRKY TFs have been identified. In this review, we summarized WRKY TFs and their functions in A. hypogaea and its donors. We also standardized the nomenclature for Arachis WRKY TFs to ensure uniformity. We determined the evolutionary relationships between Arachis and Arabidopsis thaliana WRKY (AtWRKY) TFs using a phylogenetic analysis. Biological functions and regulatory networks of Arachis WRKY TFs were predicted using AtWRKY TFs. Thus, this review paves the way for studies of Arachis WRKY TFs.

Orosomucoid proteins limit endoplasmic reticulum stress in plants

Sphingolipids are cell membrane components and signaling molecules that induce endoplasmic reticulum (ER) stress responses, but the underlying mechanism is unknown. Orosomucoid proteins (ORMs) negatively regulate serine palmitoyltransferase activity, thus helping maintain proper sphingolipid levels in humans, yeast, and plants. In this report, we explored the roles of ORMs in regulating ER stress in Arabidopsis thaliana. Loss of ORM1 and ORM2 function caused constitutive activation of the unfolded protein response (UPR), as did treatment with the ceramide synthase inhibitor Fumonisin B1 (FB1) or ceramides. FB1 treatment induced the transcription factor bZIP28 to relocate from the ER membrane to the nucleus. The transcription factor WRKY75 positively regulates the UPR and physically interacted with bZIP28. We also found that the orm mutants showed impaired ER-associated degradation (ERAD), blocking the degradation of misfolded MILDEW RESISTANCE LOCUS-O 12 (MLO-12). ORM1 and ORM2 bind to EMS-MUTAGENIZED BRI1 SUPPRESSOR 7 (EBS7), a plant-specific component of the Arabidopsis ERAD complex, and regulate its stability. These data strongly suggest that ORMs in the ER membrane play vital roles in the UPR and ERAD pathways to prevent ER stress in Arabidopsis. Our results reveal that ORMs coordinate sphingolipid homeostasis with ER quality control and play a role in stress responses.

Influence of High-Temperature and Intense Light on the Enzymatic Antioxidant System in Ginger (Zingiber officinale Roscoe) Plantlets

Environmental stressors such as high temperature and intense light have been shown to have negative effects on plant growth and productivity. To survive in such conditions, plants activate several stress response mechanisms. The synergistic effect of high-temperature and intense light stress has a significant impact on ginger, leading to reduced ginger production. Nevertheless, how ginger responds to this type of stress is not yet fully understood. In this study, we examined the phenotypic changes, malonaldehyde (MDA) content, and the response of four vital enzymes (superoxide dismutase (SOD), catalase (CAT), lipoxygenase (LOX), and nitrate reductase (NR)) in ginger plants subjected to high-temperature and intense light stress. The findings of this study indicate that ginger is vulnerable to high temperature and intense light stress. This is evident from the noticeable curling, yellowing, and wilting of ginger leaves, as well as a decrease in chlorophyll index and an increase in MDA content. Our investigation confirms that ginger plants activate multiple stress response pathways, including the SOD and CAT antioxidant defenses, and adjust their response over time by switching to different pathways. Additionally, we observe that the expression levels of genes involved in different stress response pathways, such as SOD, CAT, LOX, and NR, are differently regulated under stress conditions. These findings offer avenues to explore the stress mechanisms of ginger in response to high temperature and intense light. They also provide interesting information for the choice of genetic material to use in breeding programs for obtaining ginger genotypes capable of withstanding high temperatures and intense light stress.

MdVQ10 promotes wound-triggered leaf senescence in association with MdWRKY75 and undergoes antagonistic modulation of MdCML15 and MdJAZs in apple

Wounding stress leads to leaf senescence. However, the underlying molecular mechanism has not been elucidated. In this study, we investigated the role of the MdVQ10-MdWRKY75 module in wound-induced leaf senescence. MdWRKY75 was identified as a key positive modulator of wound-induced leaf senescence by activating the expression of the senescence-associated genes MdSAG12 and MdSAG18. MdVQ10 interacted with MdWRKY75 to enhance MdWRKY75-activated transcription of MdSAG12 and MdSAG18, thereby promoting leaf senescence triggered by wounding. In addition, the calmodulin-like protein MdCML15 promoted MdVQ10-mediated leaf senescence by stimulating the interaction between MdVQ10 and MdWRKY75. Moreover, the jasmonic acid signaling repressors MdJAZ12 and MdJAZ14 antagonized MdVQ10-mediated leaf senescence by weakening the MdVQ10-MdWRKY75 interaction. Our results demonstrate that the MdVQ10-MdWRKY75 module is a key modulator of wound-induced leaf senescence and provides insights into the mechanism of leaf senescence caused by wounding.