Synergistic effects of planting density and nitrogen fertilization on chlorophyll degradation and leaf senescence after silking in maize

Regulating planting density and nitrogen(N)fertilization could delay chlorophyll(Chl)degradation and leaf senescence in maize cultivars.This study measured changes in ear leaf green area(GLA_(ear)),Chl content,the activities of Chl a-degrading enzymes after silking,and the post-silking dry matter accumulation and grain yield under multiple planting densities and N fertilization rates.The dynamic change of GLA_(ear)after silking fitted to the logistic model,and the GLA_(ear) duration and the GLAearat 42 d after silking were affected mainly by the duration of the initial senescence period(T_(1))which was a key factor of the leaf senescence.The average chlorophyllase(CLH)activity was 8.3 times higher than pheophytinase activity and contributed most to the Chl content,indicating that CLH is a key enzyme for degrading Chl a in maize.Increasing density increased the CLH activity and decreased the Chl content,T1,GLAear,and GLA_(ear) duration.Under high density,appropriate N application reduced CLH activity,increased Chl content,prolonged T1,alleviated high-density-induced leaf senescence,and increased post-silking dry matter accumulation and grain yield.

Exogenous abscisic acid coordinating leaf senescence and transport of assimilates into wheat grains under drought stress by regulating hormones homeostasis

Drought at the grain filling stage of wheat will cause premature leaf senescence, thus leading to considerable loss of wheat yield. Therefore, this paper aims to establish a cultivation technology for strong drought resistance, delayed senescence, and yield improvement based on the analysis of hormones homeostasis obtained by applying chemical control substances. Experiments were conducted with two genotypes of wheat. Four water irrigation treatments were applied to impose the water deficit, including well-watered control treatment(WW), mild water deficit(MiWD), moderate water deficit(MoWD), and severe water deficit(SWD). Exogenous abscisic acid(ABA) was sprayed on the plants at the anthesis stage of the wheat. As a result, exogenous ABA reduced initial senescence rate(r0), total duration of chlorophyll(Chltotal), rapid senescence phase(Chlloss), and the accumulated temperature at an inflection point(M) but improved the persistence phase(Chlper) of flag leaves under all of the four treatments. However, exogenous ABA produced inconsistent effects on photoassimilate relocation and grain weight under different treatments. It produced positive regulatory effects on grain weight under WW, MiWD, and MoWD treatments. On the one hand, spraying ABA during the persistence phase of flag leaves reduced the ratios of zeatin to gibberellin(Z/GA3), spermine to spermidine(Spm/Spd), and salicylic acid to ABA(SA/ABA),which prolonged active photosynthesis by stimulating high level of proline(Pro) and increased the activities of antioxidant enzymes, such as superoxide dismutase(SOD), peroxidase(POD), catalase(CAT), and ascorbate peroxidase(APX). Therefore, drought tolerance was enhanced, and more photosynthetic assimilates were accumulated. On the other hand, the rapid senescence phase and the transport rate of assimilates into grains were accelerated, resulting in higher grain weight, yield, and water use efficiency(WUE). However, under SWD treatment, exogenous ABA improved the ratio of SA/ABA, leading to low Pro content and low antioxidant enzyme activity of flag leaves in the rapid loss phase. Meanwhile,drought resistance declined and the transport duration of assimilates into grains was shortened, thus making photosynthetic assimilates redundant. Therefore, exogenous ABA can lead to the reduction in grain weight, yield, and WUE of wheat under SWD treatment.

Mapping a leaf senescence gene els1 by BSR-Seq in common wheat

Leaf senescence is normally the last stage of plant development. Early senescence of functional leaves significantly reduces the photosynthetic time and efficiency, seriously affecting grain yield and quality in wheat. Discovering genes responsible for early leaf senescence(els) are necessary for developing novel germplasms and cultivars with delayed leaf-senescence through molecular manipulation and marker assisted selection. In this study, we identified an early leaf senescence line M114 in a derivative of a wheat breeding population. Genetic analysis indicated that early leaf senescence in M114 is controlled by a single recessive gene, provisionally designated els1. By applying bulked segregant analysis and RNA-Seq(BSR-Seq), seven polymorphic markers linked to els1 were developed and the gene was located on chromosome arm 2 BS in a 1.5 c M genetic interval between markers WGGB303 and WGGB305. A co-segregating marker, WGGB302, provide a starting point for fine mapping and map-based cloning of els1.

A rice XANTHINE DEHYDROGENASE gene regulates leaf senescence and response to abiotic stresses

Xanthine dehydrogenase, a member of the molybdenum enzyme family, participates in purine metabolism and catalyzes the generation of ureides from xanthine and hypoxanthine. However, the mechanisms by which xanthine dehydrogenase affects rice growth and development are poorly understood. In the present study, we identified a mutant with early leaf senescence and reduced tillering that we named early senescence and less-tillering 1(esl1). Map-based cloning revealed that ESL1 encodes a xanthine dehydrogenase, and it was expressed in all tissues. Chlorophyll content was reduced and chloroplast maldevelopment was severe in the esl1 mutant. Mutation of ESL1 led to decreases in allantoin, allantoate, and ABA contents. Further analysis revealed that the accumulation of reactive oxygen species in esl1 resulted in decreased photosynthesis and impaired chloroplast development, along with increased sensitivity to abscisic acid and abiotic stresses. Ttranscriptome analysis showed that the ESL1 mutation altered the expression of genes involved in the photosynthesis process and reactive oxygen species metabolism.Our results suggest that ESL1 is involved in purine metabolism and the induction of leaf senescence.These findings reveal novel molecular mechanisms of ESL1 gene-mediated plant growth and leaf senescence.

AtWRKY75 positively regulates age-triggered leaf senescence through gibberellin pathway

WRKY transcription factors play essential roles during leaf senescence.However,the mechanisms by which they regulate this process remains largely unknown.Here,we identified the transcription factor WRKY75 as a positive regulator during leaf senescence.Mutations of WRKY75 caused a delay in agetriggered leaf senescence,whereas overexpression of WRKY75 markedly accelerated this process.Expression of senescence-associated genes(SAGs)was suppressed in WRKY75 mutants but increased in WRKY75-overexpressing plants.Further analysis demonstrated that WRKY75 directly associates with the promoters of SAG12 and SAG29,to activate their expression.Conversely,GAI and RGL1,two DELLA proteins,can suppress the WRKY75-mediated activation,thereby attenuating SAG expression during leaf senescence.Genetic analyses showed that GAI gain-of-function or RGL1 overexpression can partially rescue the accelerated senescence phenotype caused by WRKY75 overexpression.Furthermore,WRKY75 can positively regulate WRKY45 expression during leaf senescence.Our data thus imply that WRKY75 may positively modulate age-triggered leaf senescence through the gibberellin-mediated signaling pathway。

Scaffold protein RACK1A positively regulates leaf senescence by coordinating the EIN3-miR164-ORE1 transcriptional cascade in Arabidopsis

Plants have adopted versatile scaffold proteins to facilitate the crosstalk between multiple signaling pathways. Leaf senescence is a well-programmed developmental stage that is coordinated by various external and internal signals. However,the functions of plant scaffold proteins in response to senescence signals are not well understood. Here, we report that the scaffold protein RACK1A(RECEPTOR FOR ACTIVATED C KINASE1A) participates in leaf senescence mediated by ethylene signaling via the coordination of the EIN3-miR164-ORE1 transcriptional regulatory cascade. RACK1A is a novel positive regulator of ethylene-mediated leaf senescence. The rack1a mutant exhibits delayed leaf senescence, while transgenic lines overexpressing RACK1A display early leaf senescence. Moreover, RACK1A promotes EIN3(ETHYLENE INSENSITIVE 3) protein accumulation, and directly interacts with EIN3 to enhance its DNA-binding activity. Together, they then associate with the miR164 promoter to inhibit its transcription, leading to the release of the inhibition on downstream ORE1(ORESARA 1) transcription and the promotion of leaf senescence.This study reveals a mechanistic framework by which RACK1A promotes leaf senescence via the EIN3-miR164-ORE1 transcriptional cascade, and provides a paradigm for how scaffold proteins finely tune phytohormone signaling to control plant development.

A molecular framework underlying low-nitrogeninduced early leaf senescence in Arabidopsis thaliana

Nitrogen(N)deficiency causes early leaf senescence,resulting in accelerated whole-plant maturation and severely reduced crop yield.However,the molecular mechanisms underlying N-deficiency-induced early leaf senescence remain unclear,even in the model species Arabidopsis thaliana.In this study,we identified Growth,Development and Splicing 1(GDS1),a previously reported transcription factor,as a new regulator of nitrate(NO3)signaling by a yeast-one-hybrid screen using a NO3enhancer fragment from the promoter of NRT2.1.We showed that GDS1 promotes NO3 signaling,absorption and assimilation by affecting the expression of multiple NO3 regulatory genes,including Nitrate Regulatory Gene2(NRG2).Interestingly,we observedthat gds1mutants show early leaf senescence as well as reduced NO3-contentand Nuptake under N-deficient conditions.Further analyses indicated that GDS1 binds to the promoters of several senescence-related genes,including Phytochrome-lnteracting Transcription Factors 4 and 5(PIF4 and PIF5)and represses their expression.Interestingly,we found that N deficiency decreases GDS1 protein accumulation,and GDS1 could interact with Anaphase Promoting Complex Subunit 10(APC10).Genetic and biochemical experiments demonstrated that Anaphase Promoting Complex or Cyclosome(APC/C)promotes the ubiquitination and degradation of GDS1 under N deficiency,resulting in loss of PIF4 and PiF5 repression and consequent early leaf senescence.Furthermore,we discovered that overexpression of GDS1 could delay leaf senescence and improve seed yield and N-use efficiency(NUE)in Arabidopsis.In summary,our study uncovers a molecular framework illustrating a new mechanism underlying low-N-induced early leaf senescence and provides potential targets for genetic improvement of crop varieties with increased yield and NUE.

ANAC087 transcription factor positively regulates age-dependent leaf senescence through modulating the expression of multiple target genes in Arabidopsis

Leaf senescence is the final stage of leaf development and appropriate onset and progression of leaf senescence are critical for reproductive success and fitness.Although great progress has been made in identifying key genes regulating leaf senescence and elucidating the underlining mechanisms in the model plant Arabidopsis,there is still a gap to understanding the complex regulatory network.In this study,we discovered that Arabidopsis ANAC087 transcription factor(TF)positively modulated leaf senescence.Expression of ANAC087 was induced in senescing leaves and the encoded protein acted as a transcriptional activator.Both constitutive and inducible overexpression lines of ANAC087 showed earlier senescence than control plants,whereas T-DNA insertion mutation and dominant repression of the ANAC087 delayed senescence rate.A quantitative reverse transcription-polymerase chain reaction(qRT-PCR)profiling showed that the expression of an array of senescence-associated genes was upregulated in inducible ANAC087 overexpression plants including BFN1,NYE1,CEP1,RbohD,SAG13,SAG15,and VPEs,which are involved in programmed cell death(PCD),chlorophyll degradation and reactive oxygen species(ROS)accumulation.In addition,electrophoretic mobility shift assay(EMSA)and chromatin immunoprecipitation-quantitative polymerase chain reaction(ChIP-qPCR)assays demonstrated that ANAC087 directly bound to the canonical NAC recognition sequence(NACRS)motif in promoters of its target genes.Moreover,mutation of two representative target genes,BFN1 or NYE1 alleviated the senescence rate of ANAC087-overexpression plants,suggesting their genetic regulatory relationship.Taken together,this study indicates that ANAC087serves as an important regulator linking PCD,ROS,and chlorophyll degradation to leaf senescence.

Melatonin retards leaf senescence by modulating phytohormone metabolism in stored Chinese flowering cabbage

This paper was conducted to explore the effects of melatonin(MT)on the senescence of stored Chinese flowering cabbage and the potential modulatory mechanisms involved.The physiological findings demonstrated that MT successfully reduced chlorophyll loss and improved the photochemical effectiveness of cabbage leaves.In addition,MT decreased the transcription of senescence-associated genes(BrSAG12)and genes responsible for chlorophyll breakdown.Transcriptome analysis showed that MT-regulated genes were enriched in oxidative phosphorylation,hormone metabolism and signal transduction,and MT treatment reduced the high expression of genes linked to generation of reactive oxygen species(ROS),energy metabolism,phytohormone(abscisic acid(ABA),ethylene(ET),and jasmonic acid(JA))biological synthesis and signal transduction while promoting the activation of genes related to scavenging ROS,energy biosynthesis and plant–pathogen interactions.We emphasized the examination of the potential interaction between phytohormone metabolism and MT.The results showed that the application of MT decreased ABA,ET,and JA levels as well as the expression of their biosynthesis genes,concurrently maintaining higher expression of cytokinin,auxin and gibberellin biosynthetic genes and lower expression of degradation genes.Regulatory networks of transcription factors(TFs)and genes related to ABA,ET and JA metabolism showed that TFs such as DNA-binding One Zinc Finger 5.7(DOF5.7),WRKY40,and homeobox-leucine zipper protein-16(ATHB-16)might play important transcriptional regulatory roles in mediating MT postponed leaf senescence.Taken together,these findings suggested that the postponed senescence of cabbage treated with MT might be ascribed to the regulated oxidative phosphorylation,energy,phytohormone metabolism,and transcription factors.

Molecular Characterization of a Leaf Senescence-Related Transcription Factor BrWRKY75 of Chinese Flowering Cabbage

WRKY is a plant-specific transcription factor(TF) involved in the regulation of many biological processes; however, its role in leaf senescence of leafy vegetables remains unknown. In the present work, a WRKY TF, termed Br WRKY75 was isolated from Chinese flowering cabbage [Brassica rapa L. ssp. chinensis(L.) Mokino var. utilis Tsen et Lee]. Analysis of deduced amino acid sequence and the phylogenetic tree showed that Br WRKY75 has high homology with WRKY75 from Brassica oleracea and Arabidopsis thaliana, and belongs to the II c sub-group. Sub-cellular localization and transcriptional activity analysis revealed that Br WRKY75 is a nuclear protein with transcriptional repression activity, and was up-regulated during leaf senescence. Electrophoretic mobility shift assay confirmed that Br WRKY75 directly bound to the W-box(TTGAC) cis-element. Collectively,these results provide a basis for further investigation of the transcriptional regulation of Chinese flowering cabbage leaf senescence.

CLE14 functions as a "brake signal" to suppress age-dependent and stress-induced leaf senescence by promoting JUB1-mediated ROS scavenging in Arabidopsis

Leaf senescence is an important developmental process in the plant life cycle and has a significant impact on agriculture.When facing harsh environmental conditions,monocarpic plants often initiate early leaf senes-cence as an adaptive mechanism to ensure a complete life cycle.Upon initiation,the senescence process is fine-tuned through the coordination of both positive and negative regulators.Here,we report that the small secreted peptide CLAVATA3/ESR-RELATED 14(CLE14)functions in the suppression of leaf senescence by regulating ROS homeostasis in Arabidopsis.Expression of the CLE14-encoding gene in leaves was signifi-cantly induced by age,high salinity,abscisic acid(ABA),salicylic acid,and jasmonic acid.CLE14 knockout plants displayed accelerated progression of both natural and salinity-induced leaf senescence,whereas increased CLE14 expression or treatments with synthetic CLE14 peptides delayed senescence.CLE14 pep-tide treatments also delayed ABA-induced senescence in detached leaves.Further analysis showed that over-expression of CLE14 led to reduced.ROS levels in leaves,where higher expression of ROS scavenging genes was detected.Moreover,CLE14 signaling resulted in transcriptional activation of JUB1,a NAC family tran-scription factor previously identified as a negative regulator of senescence.Notably,the delay of leaf senes-cence,reduction in H202 level,and activation of ROS scavenging genes by CLE14 peptides were dependent on JUB1.Collectively,these results suggest that the small peptide CLE14 serves as a novel"brake signal"to regulate age-dependent and stress-induced leaf senescence through JUB1-mediated ROS scavenging.

The NPR1-WRKY46-WRKY6 signaling cascade mediates probenazole/salicylic acid-elicited leaf senescence in Arabidopsis thaliana

Endogenous salicylic acid(SA) regulates leaf senescence, but the underlying mechanism remains largely unexplored. The exogenous application of SA to living plants is not efficient for inducing leaf senescence. By taking advantage of probenazole(PBZ)-inducedbiosynthesisof endogenous SA, we previously established a chemical inducible leaf senescence system that depends on SA biosynthesis and its core signaling receptor NPR1 in Arabidopsis thaliana. Here,using this system, we identified WRKY46 and WRKY6 as key components of the transcriptional machinery downstream of NPR1 signaling. Upon PBZ treatment, the wrky46 mutant exhibited significantly delayed leaf senescence. We demonstrate that NPR1 is essential for PBZ/SA-induced WRKY46 activation, whereas WRKY46 in turn enhances NPR1 expression. WRKY46 interacts with NPR1 in the nucleus, binding to the W-box of the WRKY6 promoter to induce its expression in response to SA signaling. Dysfunction of WRKY6 abolished PBZ-induced leaf senescence, while overexpression of WRKY6 was sufficient to accelerate leaf senescence even under normal growth conditions, suggesting that WRKY6 may serve as an integration node of multiple leaf senescence signaling pathways. Taken together,these findings reveal that the NPR1-WRKY46-WRKY6 signaling cascade plays a critical role in PBZ/SA-mediated leaf senescence in Arabidopsis.

WHIRLY1 recruits the histone deacetylase HDA15 repressing leaf senescence and flowering in Arabidopsis

Leaf senescence is controlled by a complex regulatory network in which robustness is ensured by the activity of transcription factors and epigenetic regulators.However,how these coordinate the process of leaf senescence remains poorly understood.We found that WHIRLY1 interacts with Histone Deacetylase(HDA)15,a Reduced Potassium Dependence3(RPD3)/HDA1-type HDA,by using green fluorescent protein-nanotrap-mass spectrum assays.The development-dependent interaction between WHIRLY1 and HDA15 was further confirmed by bimolecular fluorescence complementation assays and co-immunoprecipitation assays in Arabidopsis.Multi-omics genome-wide transcriptome and H3K9 acetylome enrichment analysis showed that HDA15 delays leaf senescence and flowering by repressing the expression of the positive regulators of leaf senescence and flowering,such as LOX2 and LARP1 C,and reducing H3K9 ac levels at these loci;WHIRLY1 and HDA15 co-target to the region near the transcription start site of a subset of nutrient recycling-related genes(e.g.,Glutathione S-transferases 10,non-coding RNA,and photosystem II protein D1 synthesizer attenuator PDIL1-2),as well as WRKY53 and ELF4,and co-repress their expression by removing H3K9 acetylation.Our study revealed a key transcription regulatory node of nutrient recycling and senescence-associated genes involved in leaf senescence and flowering via the recruitment of HDA15 by the single-stranded DNA/RNA-binding protein WHIRLY1.

Overexpression of the Rap2.4f transcriptional factor in Arabidopsis promotes leaf senescence

Senescence is a complex and highly regulated process. Leaf senescence is influenced by endogenous developmental and external environmental signals. In this work, we found that expression of an Ap2/DREB-type transcription factor gene, Arabidopsis Rap2.4f (At4g28140), was upregulated by salt, mannitol, and dark treatments. Constitutively overexpressing Rap2.4f under the control of the CaMV 35S promoter led to an increased chlorophyll degradation rate and upregulation of many senescence-associated genes in the transgenic Arabidopsis lines. Our results show that Rap2.4f is a positive regulator of senescence, promoting both developmental and dark-induced leaf senescence.

Verticillium dahliae Secretory Effector PevD1 Induces Leaf Senescence by Promoting ORE1-Mediated Ethylene Biosynthesis

Leaf senescence,the final stage of leaf development,is influenced by numerous internal and environmental signals.So far,how biotic stresses such as pathogen infection regulate leaf senescence is unclear.Here,we found that the premature leaf senescence caused by a soil-borne vascular fungus Verticillium dahliae in Arabidopsis was impaired by the mutation of a protein elicitor from V.dahliae 1(PevD1).Constitutive or inducible overexpression of PevD1 accelerated Arabidopsis leaf senescence.A senescence-associated NAC transcription factor,ORE1,was targeted by PevD1.PevD1 interacted with and stabilized ORE1 protein by disrupting its interaction with the RING-type ubiquitin E3 ligase NLA.Mutation of ORE1 suppressed the premature senescence caused by overexpressing PevD1.Overexpression of ORE1 or PevD1 led to enhanced ethylene production,and ORE1 mediated PevD1-induced ethylene biosynthesis by directly binding to the ACS6 promoter.Loss-of-function of ACSs suppressed V.dahliae-induced leaf senescence in ORE1-overexpressing plants.Interestingly,PevD1 also interacted with Gossypium hirsutum ORE1(GhORE1),and virus-induced gene silencing of GhORE1 delayed V.dahliae-triggered leaf senescence in cotton,indicative of the existence of a conserved mechanism in plants.Altogether,our study demonstrates that V.dahliae induces leaf senescence by secreting the effector PevD1 to regulate the ORE1-ACS6 cascade,providing new insight into biotic stress-induced senescence in plants.

Formyl tetrahydrofolate deformylase affects hydrogen peroxide accumulation and leaf senescence by regulating the folate status and redox homeostasis in rice

It is well established that an abnormal tetrahydrofolate(THF)cycle causes the accumulation of hydrogen peroxide(H_(2)O_(2))and leaf senescence,however,the molecular mechanism underlying this relationship remains largely unknown.Here,we reported a novel rice tetrahydrofolate cycle mutant,which exhibited H_(2)O_(2)accumulation and early leaf senescence phenotypes.Map-based cloning revealed that HPA1 encodes a tetrahydrofolate deformylase,and its deficiency led to the accumulation of tetrahydrofolate,5-formyl tetrahydrofolate and 10-formyl tetrahydrofolate,in contrast,a decrease in 5,10-methenyl-tetrahydrofolate.The expression of tetrahydrofolate cycle-associated genes encoding serine hydroxymethyl transferase,glycine decarboxylase and 5-formyl tetrahydrofolate cycloligase was significantly down-regulated.In addition,the accumulation of H_(2)O_(2)in hpa1 was not caused by elevated glycolate oxidation.Proteomics and enzyme activity analyses further revealed that mitochondria oxidative phosphorylation complex I and complex V were differentially expressed in hpa1,which was consistent with the H_(2)O_(2)accumulation in hpa1.In a further feeding assay with exogenous glutathione(GSH),a non-enzymatic antioxidant that consumes H_(2)O_(2),the H_(2)O_(2)accumulation and leaf senescence phenotypes of hpa1 were obviously compensated.Taken together,our findings suggest that the accumulation of H_(2)O_(2)in hpa1 may be mediated by an altered folate status and redox homeostasis,subsequently triggering leaf senescence.

Expression of the inactive ZmMEK1 induces salicylic acid accumulation and salicylic acid-dependent leaf senescence

Leaf senescence is the final leaf developmental process that is regulated by both intracellular factors and environmental conditions. The mitogen-activated protein kinase(MAPK) signaling cascades have been shown to play important roles in regulating leaf senescence; however, the component(s) downstream of the MAPK cascades in regulating leaf senescence are not fully understood. Here we showed that the transcriptions of Zm MEK1, Zm SIMK1, and Zm MPK3 were induced during dark-induced maize leaf senescence.Furthermore, in-gel kinase analysis revealed the 42 k Da MAPK was activated. Zm MEK1 interacted with Zm SIMK1 in yeast and maize mesophyll protoplasts and Zm SIMK1 was activated by Zm MEK1 in vitro. Expression of a dominant negative mutant of Zm MEK1 in Arabidopsis transgenic plants induced salicylic acid(SA) accumulation and SA-dependent leaf senescence.Zm MEK1 interacted with Arabidopsis MPK4 in yeast and High-Im pact activated MPK4 in vitro. SA treatment accelerated darkinduced maize leaf senescence. Moreover, blockage of MAPK signaling increased endogenous SA accumulation in maize leaves. These findings suggest that Zm MEK1-Zm SIMK1 cascade and its modulating SA levels play important roles in regulating leaf senescence.

Leaf senescence:progression,regulation,and application

Leaf senescence,the last stage of leaf development,is a type of postmitotic senescence and is characterized by the functional transition from nutrient assimilation to nutrient remobilization which is essential for plants’fitness.The initiation and progression of leaf senescence are regulated by a variety of internal and external factors such as age,phytohormones,and environmental stresses.Significant breakthroughs in dissecting the molecular mechanisms underpinning leaf senescence have benefited from the identification of senescence-altered mutants through forward genetic screening and functional assessment of hundreds of senescence-associated genes(SAGs)via reverse genetic research in model plant Arabidopsis thaliana as well as in crop plants.Leaf senescence involves highly complex genetic programs that are tightly tuned by multiple layers of regulation,including chromatin and transcription regulation,post-transcriptional,translational and post-translational regulation.Due to the significant impact of leaf senescence on photosynthesis,nutrient remobilization,stress responses,and productivity,much effort has been made in devising strategies based on known senescence regulatory mechanisms to manipulate the initiation and progression of leaf senescence,aiming for higher yield,better quality,or improved horticultural performance in crop plants.This review aims to provide an overview of leaf senescence and discuss recent advances in multi-dimensional regulation of leaf senescence from genetic and molecular network perspectives.We also put forward the key issues that need to be addressed,including the nature of leaf age,functional stay-green trait,coordination between different regulatory pathways,source-sink relationship and nutrient remobilization,as well as translational researches on leaf senescence.

Yang cycle enzyme DEP1: its moonlighting functions in PSI and ROS production during leaf senescence

Ethylene-mediated leaf senescence and the compromise of photosynthesis are closely associated but the underlying molecular mechanism is a mystery.Here we reported that apple DEHYDRATASE-ENOLASE-PHOSPHATASE-COMPLEX1(MdDEP1),initially characterized to its enzymatic function in the recycling of the ethylene precursor SAM,plays a role in the regulation of photosystem I(PSI)activity,activating reactive oxygen species(ROS)homeostasis,and negatively regulating the leaf senescence.A series of Y2H,Pull-down,CO-IP and Cell-free degradation biochemical assays showed that MdDEP1 directly interacts with and dephosphorylates the nucleus-encoded thylakoid protein MdY3IP1,leading to the destabilization of MdY3IP1,reduction of the PSI activity,and the overproduction of ROS in plant cells.These findings elucidate a novel mechanism that the two pathways intersect at MdDEP1 due to its moonlighting role in destabilizing MdY3IP1,and synchronize ethylene-mediated leaf senescence and the compromise of photosynthesis.

Physiological and Transcriptomic Changes During Autumn Coloration and Senescence in Ginkgo biloba Leaves

Autumn leaf senescence and coloration is a complex process and a striking natural phenomenon.Here,through biology approach integrating transcriptomic analyses in Ginkgo biloba,we determined that the content of chlorophyll decreased during leaf senescence,while carotenoid components increased until late October in the turning stage(TS)and then decreased in the yellow leaf stage(YS).Simultaneously,chlorophyll biosynthesis genes exhibited significantly lower expression levels while chlorophyll degradation genes showed increased expression from the green leaf stage(GS)to YS.However,carotenoid biosynthesis-related genes showed enhanced expression,especially in TS.An analysis of the expression of genes related to senescence demonstrated that the expression levels of most abscisic acid-and jasmonic acid-related genes,autophagy,WRKY,and NAC genes increased,whereas cytoskeleton-,photosynthesis-,and antioxidation-related genes decreased from GS to YS.Furthermore,G.biloba seedlings exogenously treated with abscisic acid,jasmonic acid,or ultraviolet-B radiation all showed obvious color variation and senescence symptoms.We used these exogenously seedlings to further validate the function of several genes involved in chlorophyll biosynthesis and senescence.Taken together,these results contribute to the elucidation of the molecular mechanisms of leaf coloration and senescence in G.biloba as well as in the identification of candidate genes involved in this process.