Identification of a Novel Gene MtbZIP60 as a Negative Regulator of Leaf Senescence through Transcriptome Analysis in Medicago truncatula.

Leaves are the primary harvest portion in forage crops such as alfalfa (Medicago sativa). Delaying leaf senescence is an effective strategy to improve forage biomass production and quality. In this study, we employed transcriptome sequencing to analyze the transcriptional changes and identify key senescence-associated genes under age-dependent leaf senescence in Medicago truncatula, a legume forage model plant. Through comparing the obtained expression data at different time points, we obtained 1057 differentially expressed genes, with 108 consistently up-regulated genes across leaf growth and senescence. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses showed that the 108 SAGs mainly related to protein processing, nitrogen metabolism, amino acid metabolism, RNA degradation and plant hormone signal transduction. Among the 108 SAGs, seven transcription factors were identified in which a novel bZIP transcription factor MtbZIP60 was proved to inhibit leaf senescence. MtbZIP60 encodes a nuclear-localized protein and possesses transactivation activity. Further study demonstrated MtbZIP60 could associate with MtWRKY40, both of which exhibited an up-regulated expression pattern during leaf senescence, indicating their crucial roles in the regulation of leaf senescence. Our findings help elucidate the molecular mechanisms of leaf senescence in M. truncatula and provide candidates for the genetic improvement of forage crops, with a focus on regulating leaf senescence.

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.

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.

Assembly and maintenance of phyllosphere microbial diversity during rubber tree leaf senescence.

Phyllosphere microorganisms execute important ecological functions including supporting host plant growth, enhancing host resistance to abiotic stresses, and promoting plant diversity. How leaf developmental stages affect plant-microbiome interactions and phyllosphere microbial community assembly and diversity is poorly understood. In this study, we utilized amplicon sequencing of 16S rRNA and ITS genes to investigate the composition and diversity of microbial communities across different leaf developmental stages of rubber trees. Our findings reveal that endophytic microbial communities, particularly bacterial communities, are more influenced by leaf senescence than by epiphytic communities. The high abundance of metabolism genes in the endosphere of yellow leaves contributes to the degradation and nutrient relocation processes. Nutrient loss leads to a higher abundance of α-Proteobacteria (r-selected microorganisms) in the yellow leaf endosphere, thereby promoting stochastic community assembly. As leaves age, the proportion of microorganisms entering the inner layer of leaves increases, consequently enhancing the diversity of microorganisms in the inner layer of leaves. These results offer insights into the mechanisms governing community assembly and diversity of leaf bacteria and fungi, thereby advancing our understanding of the evolving functions of microbial communities during leaf senescence in general, and for an important tropical crop species in particular.

Unveiling the role of epigenetics in leaf senescence: a comparative study to identify different epigenetic regulations of senescence types in barley leaves.

BACKGROUND: Developmental leaf senescence (DLS) is an irreversible process followed by cell death. Dark-induced leaf senescence (DILS) is a reversible process that allows adaptations to changing environmental conditions. As a result of exposure to adverse environmental changes, plants have developed mechanisms that enable them to survive. One of these is the redirection of metabolism into the senescence pathway. The plant seeks to optimise resource allocation. Our research aims to demonstrate how epigenetic machinery regulates leaf senescence, including its irreversibility. RESULTS: In silico analyses allowed the complex identification and characterisation of 117 genes involved in epigenetic processes in barley. These genes include those responsible for DNA methylation, post-translational histone modifications, and ATP-dependent chromatin remodelling complexes. We then performed RNAseq analysis after DILS and DLS to evaluate their expression in senescence-dependent leaf metabolism. Principal component analysis revealed that evaluated gene expression in developmental senescence was similar to controls, while induced senescence displayed a distinct profile. Western blot experiments revealed that senescence engages senescence-specific histone modification. During DILS and DLS, the methylation of histone proteins H3K4me3 and H3K9me2 increased. H3K9ac acetylation levels significantly decreased during DILS and remained unchanged during DLS. CONCLUSIONS: The study identified different epigenetic regulations of senescence types in barley leaves. These findings are valuable for exploring epigenetic regulation of senescence-related molecular mechanisms, particularly in response to premature, induced leaf senescence. Based on the results, we suggest the presence of an epigenetically regulated molecular switch between cell survival and cell death in DILS, highlighting an epigenetically driven cell survival metabolic response.

Identification of transcription factors associated with leaf senescence in tobacco.

Leaf senescence represents the final stage of leaf development, involving transcription factors (TFs)-mediated genetic reprogramming events. The timing of crop leaf senescence has a major influence on the yield and quality of crop in agricultural production. As important regulator of plant growth, the significance of TFs in the regulation of leaf senescence have been highlighted in various plant species by recent advances in genetics. However, studies on underlying molecular mechanisms are still not adequately explained. In this study, for analyzing the regulation of TFs on senescence of tobacco leaves, we combined gene differential expression analysis with weighted gene co-expression network analysis (WGCNA) to analyze the time-series gene expression profiles in senescing tobacco leaf. Among 3517 TF genes expressed in tobacco leaves, we identified 21, 35, and 183 TFs that were associated with early, middle, and late stages of tobacco leaf senescence, respectively. The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) annotation results reveal that these senescence response TFs are correlated with several biological pathways such as plant hormone signal transduction, ubiquitin mediated proteolysis and MAPK signaling pathway, indicating the roles of TFs in regulating leaf senescence. Our results provide implications for future studies of the potential regulatory mechanisms of TFs involved in senescence of tobacco leaves.

HASTY-mediated miRNA dynamics modulate nitrogen starvation-induced leaf senescence in Arabidopsis.

Nitrogen (N) deficiency responses are essential for plant survival and reproduction. Here, via an expression genome-wide association study (eGWAS), we reveal a mechanism that regulates microRNA (miRNA) dynamics necessary for N deficiency responses in Arabidopsis. Differential expression levels of three NAC transcription factor (TF) genes involved in leaf N deficiency responses among Arabidopsis accessions are most significantly associated with polymorphisms in HASTY (HST), which encodes an importin/exportin family protein responsible for the generation of mature miRNAs. HST acts as a negative regulator of N deficiency-induced leaf senescence, and the disruption and overexpression of HST differently modifies miRNA dynamics in response to N deficiency, altering levels of miRNAs targeting transcripts. Interestingly, N deficiency prevents the interaction of HST with HST-interacting proteins, DCL1 and RAN1, and some miRNAs. This suggests that HST-mediated regulation of miRNA dynamics collectively controls regulations mediated by multiple N deficiency response-associated NAC TFs, thereby being central to the N deficiency response network.

ACCELERATED CELL DEATH 6 is a crucial genetic factor shaping the natural diversity of age- and salicylic acid-induced leaf senescence in Arabidopsis.

Leaf senescence is a crucial process throughout evolution, vital for plant fitness as it facilitates the gradual shift of energy allocation between photosynthesis and catabolism overtime. This onset is influenced by a complex interplay of genetic and environmental factors, making senescence a key adaptation mechanism for plants in their natural habitats. Our study investigated the genetic mechanism underlying age-induced leaf senescence in Arabidopsis natural populations. Using a phenome high-throughput investigator, we comprehensively analyzed senescence responses across 234 Arabidopsis accessions and identified that environmental factors (e.g., ambient temperature) and physiological factors (e.g., defense responses) are substantially linked to senescence phenotypes. Through genome-wide association mapping, we identified the ACCELERATED CELL DEATH 6 (ACD6) locus as a potential regulator of senescence variation among natural accessions. Knocking out ACD6 in accessions with early and delayed senescence phenotypes resulted in varying degrees of delay in age-induced senescence, highlighting the accession-dependent regulatory role of ACD6 in leaf senescence. Furthermore, our findings suggest ACD6's involvement in senescence regulation via the salicylic acid signaling pathway. In summary, our study sheds light on the genetic regulation of leaf senescence in Arabidopsis natural populations, with the discovery of ACD6 as a potential candidate for genetic modification to enhance plant adaptation and survival.

ArNAC148 induces Acer rubrum leaf senescence by activating the transcription of the ABA receptor gene ArPYR13.

Acer rubrum, an ornamental tree known for its stunning autumn colors, has an elusive molecular mechanism that governs its leaf senescence. We performed the genome-wide analysis of NAC transcription factor genes and PYRABACTIN RESISTANCE1-LIKE (PYLs) and found that ArNAC148 and ArPYL13 were significantly upregulated in senescing leaves as compared to mature leaves. Subcellular localization studies confirmed the nuclear localization of ArNAC148 and the cytoplasmic localization of ArPYL13. Electrophoretic mobility shift assay and yeast one-hybrid assay demonstrated that ArNAC148 directly binds to the promoter of ArPYL13. Luciferase reporter assays further showed that ArNAC148 activates the transcription of ArPYL13. The transient expression of ArNAC148 and ArPYL13 in tobacco leaves promoted chlorophyll degradation, increased H2O2 level, MDA contents, and electrolyte leakage in response to abscisic acid (ABA). Moreover, the virus-induced gene silencing of ArNAC148 and ArPYL13 in A. rubrum produced results that were opposite to those observed in transient expression experiments. Our findings suggest that ArNAC148 induces leaf senescence by directly activating the transcription of ArPYL13, providing insights into the ABA-mediated regulatory mechanisms governing leaf senescence in A. rubrum. This study offers new perspectives for researchers to explore the roles of NAC and PYL genes in regulating leaf senescence in woody ornamental plants.

A chemical approach to extend flower longevity of Japanese morning glory via inhibition of master senescence regulator EPHEMERAL1.

Petal senescence in flowering plants is a type of programmed cell death with highly regulated onset and progression. A NAM/ATAF1,2/CUC2 transcription factor, EPHEMERAL1 (EPH1), has been identified as a key regulator of petal senescence in Japanese morning glory (Ipomoea nil). Here we used a novel chemical approach to delay petal senescence in Japanese morning glory by inhibiting the DNA-binding activity of EPH1. A cell-free high-throughput screening system and subsequent bioassays found two tetrafluorophthalimide-based compounds, Everlastin1 and Everlastin2, that inhibited the EPH1-DNA interaction and delayed petal senescence. The inhibitory mechanism was due to the suppression of EPH1 dimerization. RNA-sequencing analysis revealed that the chemical treatment strongly suppressed the expression of programmed cell death- and autophagy-related genes. These results suggest that a chemical approach targeting a transcription factor can regulate petal senescence.

Telomerase reverse transcriptase, a telomere length maintenance protein in alfalfa (Medicago sativa), confers Arabidopsis thaliana seeds aging tolerance via modulation of telomere length.

Numerous studies have investigated seed aging, with a particular emphasis on the involvement of reactive oxygen species. Reactive oxygen species diffuse into the nucleus and damage telomeres, resulting in loss of genetic integrity. Telomerase reverse transcriptase (TERT) plays an essential role in maintaining plant genomic stability. Genome-wide analyses of TERT genes in alfalfa (Medicago sativa) have not yet been conducted, leaving a gap in our understanding of the mechanisms underlying seed aging associated with TERT genes. In this study, four MsTERT genes were identified in the alfalfa genome. The expression profiles of the four MsTERT genes during seed germination indicated that MS. gene79077 was significantly upregulated by seed aging. Transgenic seeds overexpressing MS. gene79077 in Arabidopsis exhibited enhanced tolerance to seed aging by reducing the levels of H2O2 and increasing telomere length and telomerase activity. Furthermore, transcript profiling of aging-treated Arabidopsis wild-type and overexpressing seeds showed an aging response in genes related to glutathione-dependent detoxification and antioxidant defense pathways. These results revealed that MS. gene79077 conferred Arabidopsis seed-aging tolerance via modulation of antioxidant defense and telomere homeostasis. This study provides a new way to understand stress-responsive MsTERT genes for the potential genetic improvement of seed vigor.

Transcriptome-Wide Identification of Dark- and Salt-Induced Senescence-Related NAC Gene Family Members in Alfalfa.

Leaves are a key forage part for livestock, and the aging of leaves affects forage biomass and quality. Preventing or delaying premature leaf senescence leads to an increase in pasture biomass accumulation and an improvement in alfalfa quality. NAC transcription factors have been reported to affect plant growth and abiotic stress responses. In this study, 48 NAC genes potentially associated with leaf senescence were identified in alfalfa under dark or salt stress conditions. A phylogenetic analysis divided MsNACs into six subgroups based on similar gene structure and conserved motif. These MsNACs were unevenly distributed in 26 alfalfa chromosomes. The results of the collinearity analysis show that all of the MsNACs were involved in gene duplication. Some cis-acting elements related to hormones and stress were screened in the 2-kb promoter regions of MsNACs. Nine of the MsNAC genes were subjected to qRT-PCR to quantify their expression and Agrobacterium-mediated transient expression to verify their functions. The results indicate that Ms.gene031485, Ms.gene032313, Ms.gene08494, and Ms.gene77666 might be key NAC genes involved in alfalfa leaf senescence. Our findings extend the understanding of the regulatory function of MsNACs in leaf senescence.

The AtMINPP Gene, Encoding a Multiple Inositol Polyphosphate Phosphatase, Coordinates a Novel Crosstalk between Phytic Acid Metabolism and Ethylene Signal Transduction in Leaf Senescence.

Plant senescence is a highly coordinated process that is intricately regulated by numerous endogenous and environmental signals. The involvement of phytic acid in various cell signaling and plant processes has been recognized, but the specific roles of phytic acid metabolism in Arabidopsis leaf senescence remain unclear. Here, we demonstrate that in Arabidopsis thaliana the multiple inositol phosphate phosphatase (AtMINPP) gene, encoding an enzyme with phytase activity, plays a crucial role in regulating leaf senescence by coordinating the ethylene signal transduction pathway. Through overexpressing AtMINPP (AtMINPP-OE), we observed early leaf senescence and reduced chlorophyll contents. Conversely, a loss-of-function heterozygous mutant (atminpp/+) exhibited the opposite phenotype. Correspondingly, the expression of senescence-associated genes (SAGs) was significantly upregulated in AtMINPP-OE but markedly decreased in atminpp/+. Yeast one-hybrid and chromatin immunoprecipitation assays indicated that the EIN3 transcription factor directly binds to the promoter of AtMINPP. Genetic analysis further revealed that AtMINPP-OE could accelerate the senescence of ein3-1eil1-3 mutants. These findings elucidate the mechanism by which AtMINPP regulates ethylene-induced leaf senescence in Arabidopsis, providing insights into the genetic manipulation of leaf senescence and plant growth.

Leaf drought adaptive response in winter oilseed rape is altered at the onset of senescence: a study combining NMR relaxometry, multi-omics and microscopy.

Climate change is bringing more frequent and intense droughts, reducing overall water availability and adversely affecting crops. There is a need to improve our understanding of the tissular and cellular adaptation mechanisms that are critical for plant water conservation strategies. Here, we have used NMR relaxometry in combination with microscopy and multi-omic analysis to study the effects of progressive soil drought on winter oilseed rape (WOSR, Brassica napus L., cv. Aviso) leaves. This study reveals the structural and metabolic adjustments these leaves operate to maintain cell homeostasis. Our results are original in showing that the adaptive responses are altered in leaves at the onset of senescence, associated with changes in metabolic plasticity and mesophyll structures. Thus, long-term responses in young leaves involving osmotic adjustment were combined with the maintenance of tissue hydration and cell growth, contributing to high survival and recovery capacity. For the first time, short-term responses observed in early senescent-old leaves were associated with early drought-induced dehydration of the spongy layer. However, this dehydration was not followed by osmotic adjustment and did not allow maintenance of leaf tissue turgor. These findings open further studies on the genetic variability of drought responses related to identified short- and long-term structural and metabolic plasticity traits in Brassica species.

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.

Soybean ethylene response factors GmENS1 and GmENS2 promote nodule senescence.

The final phase in root nodule development is nodule senescence. The mechanism underlying the initiation of nodule senescence requires further elucidation. In this study, we investigate the intrinsic signals governing soybean (Glycine max L. Merr.) nodule senescence, uncovering ethylene as a key signal in this intricate mechanism. Two AP2/ethylene response factor (ERF) transcription factor (TF) genes, GmENS1 and GmENS2 (Ethylene-responsive transcription factors required for Nodule Senescence), exhibit heightened expression levels in both aged nodules and nodules treated with ethylene. An overexpression of either GmENS1 or GmENS2 accelerates senescence in soybean nodules, whereas the knockout or knockdown of both genes delays senescence and enhances nitrogenase activity. Furthermore, our findings indicate that GmENS1 and GmENS2 directly bind to the promoters of GmNAC039, GmNAC018, and GmNAC030, encoding 3 NAC (NAM, ATAF1/2, and CUC2) TFs essential for activating soybean nodule senescence. Notably, the nodule senescence process mediated by GmENS1 or GmENS2 overexpression is suppressed in the soybean nac039/018/030 triple mutant compared with the wild-type control. These data indicate GmENS1 and GmENS2 as pivotal TFs mediating ethylene-induced nodule senescence through the direct activation of GmNAC039/GmNAC018/GmNAC030 expression in soybean.

Genetic Analysis and Fine Mapping of a New Rice Mutant, Leaf Tip Senescence 2.

Premature leaf senescence significantly reduces rice yields. Despite identifying numerous factors influencing these processes, the intricate genetic regulatory networks governing leaf senescence demand further exploration. We report the characterization of a stably inherited, ethyl methanesulfonate(EMS)-induced rice mutant with wilted leaf tips from seedling till harvesting, designated lts2. This mutant exhibits dwarfism and early senescence at the leaf tips and margins from the seedling stage when compared to the wild type. Furthermore, lts2 displays a substantial decline in both photosynthetic activity and chlorophyll content. Transmission electron microscopy revealed the presence of numerous osmiophilic granules in chloroplast cells near the senescent leaf tips, indicative of advanced cellular senescence. There was also a significant accumulation of H2O2, alongside the up-regulation of senescence-associated genes within the leaf tissues. Genetic mapping situated lts2 between SSR markers Q1 and L12, covering a physical distance of approximately 212 kb in chr.1. No similar genes controlling a premature senescence leaf phenotype have been identified in the region, and subsequent DNA and bulk segregant analysis (BSA) sequencing analyses only identified a single nucleotide substitution (C-T) in the exon of LOC_Os01g35860. These findings position the lts2 mutant as a valuable genetic model for elucidating chlorophyll metabolism and for further functional analysis of the gene in rice.

Overexpression of MtIPT gene enhanced drought tolerance and delayed leaf senescence of creeping bentgrass (Agrostis stolonifera L.).

BACKGROUND: Isopentenyltransferases (IPT) serve as crucial rate-limiting enzyme in cytokinin synthesis, playing a vital role in plant growth, development, and resistance to abiotic stress. RESULTS: Compared to the wild type, transgenic creeping bentgrass exhibited a slower growth rate, heightened drought tolerance, and improved shade tolerance attributed to delayed leaf senescence. Additionally, transgenic plants showed significant increases in antioxidant enzyme levels, chlorophyll content, and soluble sugars. Importantly, this study uncovered that overexpression of the MtIPT gene not only significantly enhanced cytokinin and auxin content but also influenced brassinosteroid level. RNA-seq analysis revealed that differentially expressed genes (DEGs) between transgenic and wild type plants were closely associated with plant hormone signal transduction, steroid biosynthesis, photosynthesis, flavonoid biosynthesis, carotenoid biosynthesis, anthocyanin biosynthesis, oxidation-reduction process, cytokinin metabolism, and wax biosynthesis. And numerous DEGs related to growth, development, and stress tolerance were identified, including cytokinin signal transduction genes (CRE1, B-ARR), antioxidase-related genes (APX2, PEX11, PER1), Photosynthesis-related genes (ATPF1A, PSBQ, PETF), flavonoid synthesis genes (F3H, C12RT1, DFR), wax synthesis gene (MAH1), senescence-associated gene (SAG20), among others. CONCLUSION: These findings suggest that the MtIPT gene acts as a negative regulator of plant growth and development, while also playing a crucial role in the plant's response to abiotic stress.

Plastid-expressed AdDjSKI enhances photosystem II stability, delays leaf senescence, and increases fruit yield in tomato plants under heat stress.

Heat stress substantially reduces tomato (Solanum lycopersicum) growth and yield globally, thereby jeopardizing food security. DnaJ proteins, constituents of the heat shock protein system, protect cells from diverse environmental stresses as HSP-70 molecular co-chaperones. In this study, we demonstrated that AdDjSKI, a serine-rich DnaJ III protein induced by pathogens, plays an important role in stabilizing photosystem II (PSII) in response to heat stress. Our results revealed that transplastomic tomato plants expressing the AdDjSKI gene exhibited increased levels of total soluble proteins, improved growth and chlorophyll content, reduced malondialdehyde (MDA) accumulation, and diminished PSII photoinhibition under elevated temperatures when compared with wild-type (WT) plants. Intriguingly, these transplastomic plants maintained higher levels of D1 protein under elevated temperatures compared with the WT plants, suggesting that overexpression of AdDjSKI in plastids is crucial for PSII protection, likely due to its chaperone activity. Furthermore, the transplastomic plants displayed lower accumulation of superoxide radical (O2 •─) and H2O2, in comparison with the WT plants, plausibly attributed to higher superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities. This also coincides with an enhanced expression of corresponding genes, including SlCuZnSOD, SlFeSOD, SlAPX2, and SltAPX, under heat stress. Taken together, our findings reveal that chloroplastic expression of AdDjSKI in tomatoes plays a critical role in fruit yield, primarily through a combination of delayed senescence and stabilizing PSII under heat stress.

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.