Accelerated Leaf Senescence Research Articles

Heat Shock Factor HSFA6b Mediates Mitochondrial Unfolded Protein Response in Arabidopsis thaliana

Mitochondria are important organelles in eukaryotes and are involved in various metabolic processes. Mitochondrial proteotoxic stress triggers the mitochondrial unfolded protein response (UPRmt) to restore mitochondrial protein homeostasis and maintain normal life activities. However, the regulatory mechanism of plant UPRmt remains to be revealed in Arabidopsis. Based on the fact that UPRmt activates heat shock protein (HSP) genes, we identified the heat shock transcription factor HSFA6b as a key regulator mediating UPRmt through reverse genetics. HSFA6b responded to mitochondrial proteotoxic stress and regulated mitochondrial heat shock proteins’ genes’ (mtHSPs) expression. HSFA6b translocated to the nuclear after treatment with doxycycline (Dox)—a mitochondrial ribosome translation inhibitor. HSFA6b binds to the mtHSPs promoters and activates mtHSPs expression. The HSFA6b mutation blocked the UPRmt signals to promote root growth under mitochondrial proteotoxic stress and accelerated leaf senescence during development. Our study reveals a novel signal-regulating mechanism in the UPRmt pathways and provides new insights regarding the regulation of plant growth and development and stress resistance by the UPRmt pathways.

Effect of High Nighttime Temperatures on Growth, Yield, and Quality of Two Wheat Cultivars During the Whole Growth Period.

It is a consensus that Earth's climate has been warming. The impact of global warming is asymmetric, that is, there is more substantial warming in the daily minimum surface air temperature and lower warming in the maximum surface air temperature. Previous studies have reported diurnal temperature differences greatly affecting winter wheat yield. However, only a few studies have investigated the impact of global warming on the growth and yield of winter wheat, yet the influence of night warming on quality has not been deeply evaluated. In this study, two wheat cultivars were used as materials: Jimai 44 (JM44) with strong gluten and Jimai 22 (JM22) with medium gluten, to explore the effects of high nighttime temperatures (HNTs) on the growth, yield, and quality of wheat. The results show that HNTs significantly shortened seedling emergence and anthesis periods in both cultivars compared with ambient temperatures (ATs). In addition, HNTs increased the respiration rate at anthesis and grain-filling stages, impeding wheat pollination and grain maturity. HNTs also accelerated leaf senescence and increased the number of sterile spikelets and plant height, but decreased the effective tiller number, the number of spikes per unit area, and grains per spike. As a result, the grain yield of JM22 and JM44 was decreased by 24.6% and 21.2%, respectively. Moreover, HNTs negatively influenced the flour quality of the two wheat cultivars. The current findings provide new insights into the effects of HNTs on the growth, development, yield, and quality of different wheat genotypes during the whole growth period.

SCOOP10 And SCOOP12 Peptides Act Through MIK2 Receptor-Like Kinase to Antagonistically Regulate Arabidopsis Leaf Senescence

Leaf senescence plays a critical role in a plant's overall reproductive success due to its involvement in nutrient remobilization and allocation. However, our current understanding of the molecular mechanisms controlling leaf senescence remains limited. In this study, we demonstrate that the receptor-like kinase MALE DISCOVERER 1-INTERACTING RECEPTOR-LIKE KINASE 2 (MIK2) functions as a negative regulator of leaf senescence. We report that the SERINE-RICH ENDOGENOUS PEPTIDE 12, previously known to physically interact with MIK2, competes with SCOOP10 to control MIK2-dependent senescence regulatory mechanisms. We observed that increased expression of SCOOP10 or the application of exogenous SCOOP10 peptides accelerated leaf senescence in a MIK2-dependent manner. Conversely, SCOOP12 acted as a suppressor of MIK2-dependent senescence regulation. We also found that SCOOP12 enhanced while SCOOP10 diminished MIK2 phosphorylation. Thus, the SCOOP12-MIK2 module might function antagonistically on SCOOP10-MIK2 signaling at late senescing stages, allowing for fine-tuned modulation of the leaf senescence process. Our research sheds light on the complex mechanisms underlying leaf senescence and provides valuable insights into the interplay between receptors, peptides, and the regulation of plant senescence.

OsCNGC7 modulates calcium dynamics and accelerates leaf senescence in rice

Calcium plays a crucial role in regulating plant senescence. However, the specific effects of increased intranuclear calcium versus cytoplasmic calcium on aging remain unclear. Cyclic nucleotide-gated channels (CNGCs), which manage Ca2⁺ levels in plant cells, are particularly significant in this context. These channels are known to relocate between the nuclear envelope and the plasma membrane in response to stress and developmental signals. Through this movement, CNGCs help regulate the balance of cytosolic and intranuclear Ca2⁺. In this study, we categorized the 16 CNGC genes in rice into five subgroups. OsCNGCs are notably expressed in leaves, especially during the reproductive stage. Both OsCNGC6 and OsCNGC7 exhibit dual localization to the plasma membrane and the nuclear envelope. Knockdown of OsCNGC7 led to reduced levels of Ca2⁺ and K⁺ in plants. Conversely, yeast expressing the OsCNGC7 gene showed increased sensitivity to Ca2⁺. Additionally, while the [Ca2⁺]cyt was maintained at relatively low levels in both wild-type and OsCNGC7-RNAi lines, the fluorescence intensity was significantly higher in OsCNGC7-overexpressing lines, particularly in the nucleus of root tips. Overexpression of OsCNGC7 resulted in enhanced stomatal opening and accelerated leaf senescence from the tillering stage to grain filling in rice. Treatment with MeJA rapidly induced OsCNGC7 expression, while knockdown of OsCNGC7 delayed both MeJA-induced and dark-induced leaf senescence. Further analysis revealed that OsCNGC7 interacts with OsKAT2 and OsALMT2. In conclusion, our findings highlight the distinct roles of OsCNGCs in regulating senescence. This knowledge could provide new strategies for manipulating plant senescence and enhancing crop productivity.

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.

Knockdown of SlYTHDF2 Accelerates Dark-Induced Tomato Leaf Senescence by Affecting the ABA Pathway.

N6-methyladenosine (m6A) is a widespread post-transcriptional modification in eukaryotic mRNAs. Proteins with the YTH structural domain act as m6A-binding proteins by recognizing the m6A modification and regulating mRNA through this recognition. In this study, SlYTHDF2, a prototypical m6A -binding protein gene in the YTH family was expressed in various tissues, and subcellular localization analyses indicated that the SlYTHDF2 protein was localized in the nucleus and cytoplasm. SlYTHDF2 knockout lines were obtained using CRISPR/Cas9 technology and showed the senesced leaves prematurely increased endogenous ABA accumulation compared with the wild type. Moreover, we found that dark promoted leaf senescence in SlYTHDF2 knockout lines and exogenous ABA further accelerated leaf senescence under dark conditions. The qRT-PCR analysis revealed significant alterations in the expression of genes associated with the ABA pathway. Relative to the wild type, the CR-slythdf2 plants exhibited reduced levels of photosynthetic pigments, higher accumulation of reactive oxygen species, and increased damage to cell membranes. Additionally, we discovered that SlYTHDF2 interacts with the chloroplast-binding protein SlRBCS3 through yeast two-hybrid and BiFC experiments. Overall, our data suggest the important role of SlYTHDF2 in regulating tomato leaf senescence.

An osmesl mutant delayed rice leaf senescence through inhibiting cell death by OsBI-1

Leaf senescence following heading in rice is subject to rigorous regulation, with many of the underlying control mechanisms remaining largely unknown. In this study, we identified a novel gene, OsMESL, which exerts a positive regulatory effect on leaf senescence in rice. The T-DNA insertion mutant known as osmesl and RNA interference plants displayed a phenotype characterized by stay-green after heading. Genetic analysis indicated that the mutant phenotype could be rescued through complementation, while the overexpression of OsMESL accelerated leaf senescence after heading, underscoring OsMESL's positive regulatory role in rice leaf senescence. Subsequent investigations revealed that OsMESL modulates the process of cell death by influencing the stability of its interacting protein, the cell death suppressor OsBI-1, thereby governing leaf senescence. Furthermore, the leaves of the osmesl mutant exhibited a delayed reduction in photosynthesis, along with increased grain length and 1000-grain weight. In conclusion, we identified OsMESL as a novel positive regulator of leaf senescence in rice, which likely participates in leaf senescence through the mediation of cell death by OsBI-1, resulting in the phenotype of stay-green in the osmesl mutant after heading.

The MYB transcriptional factor BrMYB108 regulates Auxin-mediated delayed leaf senescence in postharvest Pak Choi

Auxin is the earliest discovered class of endogenous plant hormones, widely distributed in higher plants, and plays a key role in regulating plant growth and development. However, the molecular mechanism by which auxin affects postharvest leaf senescence in pak choi (Brassica rapa subsp. chinensis) remains unclear. In this study, we found that exogenous application of 2 mg L−1 of the auxin analog indoleacetic acid (IAA) could delay postharvest leaf senescence in pak choi. Importantly, we isolated an R2R3-MYB transcription factor (TF), BrMYB108, which was highly expressed in senescent leaves and whoes expression was suppressed by IAA treatment. Molecular evidence confirmed that BrMYB108 can bind to the promoter region of the chlorophyll metabolism gene BrSGR2 to activate its expression. Heterologous expression of BrMYB108 in Arabidopsis accelerated leaf senescence, while silencing BrMYB108 in pak choi using virus induced gene silencing (VIGS) delayed leaf senescence. In addition, we found that BrMYB108 is a direct target gene of the auxin response factor 17 (ARF17) homolog gene, BrARF17, in Arabidopsis. Our study reveals a model in which BrARF17 regulates postharvest leaf senescence in pak choi by targeting the expression of BrMYB108. These molecular insights into the auxin-mediated regulation of postharvest leaf senescence in pak choi have positive implications for manipulating BrMYB108 to improve the postharvest shelf life of vegetables.

RsOBP2a, a member of OBF BINDING PROTEIN transcription factors, inhibits two chlorophyll degradation genes in green radish

The green radish (Raphanus sativus L.) contains abundant chlorophyll (Chl). DOF-type transcription factor OBF BINDING PROTEIN (OBP) plays crucial functions in plant growth, development, maturation and responses to various abiotic stresses. However, the metabolism by which OBP transcription factors regulate light-induced Chl metabolism in green radish is not well understood. In this study, six OBP genes were identified from the radish genome, distributed unevenly across five chromosomes. Among these genes, RsOBP2a showed significantly higher expression in the green flesh compared to the white flesh of green radish. Analysis of promoter elements suggested that RsOBPs might be involved in stress responses, particularly in light-related processes. Overexpression of RsOBP2a led to increase Chl levels in cotyledons and adventitious roots of radish, while silencing RsOBP2a expression through TYMV-induced gene silencing accelerated leaf senescence. Further investigations revealed that RsOBP2a was localized in the nucleus and served as a transcriptional repressor. RsOBP2a was induced by light and directly suppressed the expression of STAYGREEN (SGR) and RED CHLOROPHYLL CATABOLITE REDUCTASE (RCCR), thereby delaying senescence in radish. Overall, a novel regulatory model involving RsOBP2a, RsSGR, and RsRCCR was proposed to govern Chl metabolism in response to light, offering insights for the enhancement of green radish germplasm.

Weak-light stress at different grain filling stages affects yield by reducing leaf carbon and nitrogen metabolism in fresh waxy maize

Insufficient light radiation is one of the main factors limiting maize yield in southern China. The plum rainy season overlaps with grain filling stage, and intermittent cloudy and rainy weather results in weak-light stress restricting the yield improvement of fresh waxy maize. This study was to assess the impact of weak-light stress at different grain filling stages on yield and leaf carbon (C) and nitrogen (N) metabolism in fresh waxy maize. Suyunuo5 (SYN5) and Jingkenuo2000 (JKN2000) were used to investigate the effects of weak-light at different stages after pollination (1–7, 8–14, 15–21 and 1–21 days, recorded as Z1, Z2, Z3 and Z4) on yield, dry matter and nitrogen (N) accumulation, C and N metabolism in leaf of fresh waxy maize from 2021 to 2022. Compared with CK (natural light treatment), weak-light decreased the fresh ear and grain yield, post-silking dry matter and N accumulation, and the decrease was maximum in Z4, followed by Z1. The decrease in JKN2000 was greater than SYN5. RUBPCase and PEPCase activities, net photosynthetic rate, transpiration rate and stomatal conductance of ear leaves decreased under weak-light, and those were lowest in Z4, followed by Z1. Furthermore, weak-light stress significantly decreased the activities of nitrate reductase, glutamine synthetase, glutamate synthase, and post-silking N accumulation. The highest decrease was found in Z4, followed by Z1. Weak-light stress also downregulated the activities of superoxide dismutase, catalase, peroxidase and raised MDA content in ear leaves during grain filling stage, which accelerated leaf senescence process. Weak-light stress after pollination decreased maize yield by affecting leaf C and N metabolism and antioxidant system, and the stress occurred in first week after pollination had a more severe impact than those in middle and later stages, and JKN2000 was more sensitive to weak-light than SYN5. Our results contributed to understanding how weak-light stress could reduce the yield of fresh waxy maize by affecting leaf C and N metabolism, and offered theoretical support for implementing measures to alleviate weak-light conditions in the planting areas of fresh waxy maize.

Cultivar-specific regulation of antioxidant enzyme activity and stomatal closure confer tolerance of wheat to elevated ozone: A two-year open-field study with five cultivars

Elevated concentrations of tropospheric ozone (O3) pose a significant threat to food production in many regions of the world. We conducted a two-year experiment with five winter wheat (Triticum aestivum L.) cultivars, Yangmai16 (Y16), Yangmai23 (Y23), Zhenmai12 (Z12), Yangmai29 (Y29), and Yangmai30 (Y30), to assess photosynthetic traits, lipid peroxidation, and antioxidant systems under ambient (A-O3) or elevated (E-O3; 1.5 times A-O3) O3 in a Free-Air O3Concentration Enrichment system (FACE). E-O3 accelerated leaf senescence, manifested by marked reductions in photosynthetic rate, stomatal conductance, total antioxidant capacity, and photosynthetic pigment content, accompanied by altered antioxidant enzyme activity and a significant increase in malondialdehyde content (an indicator of lipid peroxidation). Most parameters showed significant inter-cultivar differences, as well as interactions between O3 and cultivar. The response of the antioxidant system in wheat flag leaves was influenced by O3 exposure levels. The response of antioxidant enzymes at the grain filling stage and the timely closure of stomata conferred tolerance to O3. This tolerance was associated with higher antioxidant enzyme activity at the anthesis stage but was not related to the size of stomata. This study provides a crucial theoretical foundation for further breeding O3-tolerant cultivars.

Alterations in the Anatomy and Ultrastructure of Leaf Blade in Norway Maple (Acer platanoides L.) Growing on Mining Sludge: Prospects of Using This Tree Species for Phytoremediation.

Alterations in leaf architecture can be used as an indicator of the substrate toxicity level as well as the potential of a given plant species in the phytoremediation of polluted areas, e.g., mining sludge. In this work, we demonstrated, for the first time, the nature and scale of alterations in leaf architecture at the tissue and cellular levels occurring in Norway maple growing on mining sludge originating from a copper mine in Lubin (Poland). The substrate differs from other mine wastes, e.g., calamine or serpentine soils, due to an extremely high level of arsenic (As). Alterations in leaf anatomy predominantly included the following: (1) a significant increase in upper epidermis thickness; (2) a significant decrease in palisade parenchyma width; (3) more compact leaf tissue organization; (4) the occurrence of two to three cell layers in palisade parenchyma in contrast to one in the control; (5) a significantly smaller size of cells building palisade parenchyma. At the cellular level, the alterations included mainly the occurrence of local cell wall thickenings-predominantly in the upper and lower epidermis-and the symptoms of accelerated leaf senescence. Nevertheless, many chloroplasts showed almost intact chloroplast ultrastructure. Modifications in leaf anatomy could be a symptom of alterations in morphogenesis but may also be related to plant adaptation to water deficit stress. The occurrence of local cell wall thickenings can be considered as a symptom of a defence strategy involved in the enlargement of apoplast volume for toxic elements (TE) sequestration and the alleviation of oxidative stress. Importantly, the ultrastructure of leaf cells was not markedly disturbed. The results suggested that Norway maple may have good phytoremediation potential. However, the general shape of the plant, the significantly smaller size of leaves, and accelerated senescence indicated the high toxicity of the mining sludge used in this experiment. Hence, the phytoremediation of such a substrate, specifically including use of Norway maple, should be preceded by some amendments-which are highly recommended.

Casein kinase 1 AELs promote senescence by enhancing ethylene biosynthesis through phosphorylating WRKY22 transcription factor.

Leaf senescence is a complex process regulated by developmental and environmental factors, and plays a pivotal role in the development and life cycle of higher plants. Casein kinase 1 (CK1) is a highly conserved serine/threonine protein kinase in eukaryotes and functions in various cellular processes including cell proliferation, light signaling and hormone effects of plants. However, the biological function of CK1 in plant senescence remains unclear. Through systemic genetic and biochemical studies, we here characterized the function of Arabidopsis EL1-like (AEL), a CK1, in promoting leaf senescence by stimulating ethylene biosynthesis through phosphorylating transcription factor WRKY22. Seedlings lacking or overexpressing AELs presented delayed or accelerated leaf senescence, respectively. AELs interact with and phosphorylate WRKY22 at Thr57, Thr60 and Ser69 residues to enhance whose transactivation activity. Being consistent, increased or suppressed phosphorylation of WRKY22 resulted in the promoted or delayed leaf senescence. WRKY22 directly binds to promoter region and stimulates the transcription of 1-amino-cyclopropane-1-carboxylate synthase 7 gene to promote ethylene level and hence leaf senescence. Our studies demonstrated the crucial role of AEL-mediated phosphorylation in regulating ethylene biosynthesis and promoting leaf senescence by enhancing WRKY22 transactivation activity, which helps to elucidate the fine-controlled ethylene biosynthesis and regulatory network of leaf senescence.

Delayed senescence and crop performance under stress: always a functional couple?

Exposure to abiotic stresses accelerates leaf senescence in most crop plant species, thereby reducing photosynthesis and other assimilatory processes. In some cases, genotypes with delayed leaf senescence (i.e. 'stay-green') show stress resistance, particularly in cases of water deficit, and this has led to the proposal that senescence delay improves crop performance under some abiotic stresses. In this review, we summarize the evidence for increased resistance to abiotic stress, mostly water deficit, in genotypes with delayed senescence, and specifically focus on the physiological mechanisms and agronomic conditions under which the stay-green trait may ameliorate grain yield under stress.

Modeling the effects of tropospheric ozone on the growth and yield of global staple crops with DSSAT v4.8.0

Abstract. Elevated surface ozone (O3) concentrations can negatively impact growth and development of crop production by reducing photosynthesis and accelerating leaf senescence. Under unabated climate change, future global O3 concentrations are expected to increase in many regions, adding additional challenges to global agricultural production. Presently, few global process-based crop models consider the effects of O3 stress on crop growth. Here, we incorporated the effects of O3 stress on photosynthesis and leaf senescence into the Decision Support System for Agrotechnology Transfer (DSSAT) crop models for maize, rice, soybean, and wheat. The advanced models reproduced the reported yield declines from observed O3-dose field experiments and O3 exposure responses reported in the literature (O3 relative yield loss RMSE <10 % across all calibrated models). Simulated crop yields decreased as daily O3 concentrations increased above 25 ppb, with average yield losses of 0.16 % to 0.82 % (maize), 0.05 % to 0.63 % (rice), 0.36 % to 0.96 % (soybean), and 0.26 % to 1.23 % (wheat) per ppb O3 increase, depending on the cultivar O3 sensitivity. Increased water deficit stress and elevated CO2 lessen the negative impact of elevated O3 on crop yield, but potential yield gains from CO2 concentration increases may be counteracted by higher O3 concentrations in the future, a potentially important constraint to global change projections for the latest process-based crop models. The improved DSSAT models with O3 representation simulate the effects of O3 stress on crop growth and yield in interaction with other growth factors and can be run in the parallel DSSAT global gridded modeling framework for future studies on O3 impacts under climate change and air pollution scenarios across agroecosystems globally.

Transcriptome Sequencing Provides Insights into High-Temperature-Induced Leaf Senescence in Herbaceous Peony

Global warming causes frequent high temperatures in summer; which negatively impacts herbaceous peonies (Paeonia lactiflora Pall.) by accelerating leaf senescence and reducing biomass accumulation, leading to reduced flower quality in the subsequent year. Our findings revealed that as heat stress progressed, the high-temperature-sensitive cultivar ‘Meigui Zi’ (MGZ) exhibited a higher rate of chlorophyll content reduction and more pronounced premature aging symptoms than the high-temperature-tolerant cultivar ‘Chi Fen’ (CF). To investigate gene expression differences between CF and MGZ under high-temperature stress, we combined PacBio Iso-Seq sequencing (Iso-Seq) with next-generation sequencing (RNA-seq). Iso-seq yielded 352,891 full-length transcripts ranging from 61 bp to 49,022 bp in length. RNA-seq generated 257,562 transcripts across all samples. Further analysis revealed that differentially expressed genes (DEGs) between CF and MGZ were primarily enriched in “Photosynthesis”, with most photosynthesis-related DEGs highly expressed in CF. This indicates that CF has higher stability in its photosystem compared with MGZ, which is crucial for mitigating leaf senescence caused by high temperatures. Additionally, the highly expressed chlorophyll degradation genes stay-green (SGR) and stay-green-like (SGRL) in MGZ may be involved in chlorophyll content reduction induced by high temperature. This study preliminarily revealed the molecular mechanism of high-temperature-induced leaf senescence of in herbaceous peony and provided candidate genes for further studies of the regulation mechanism of high -temperature-induced leaf senescence.

Rice ONAC016 promotes leaf senescence through abscisic acid signaling pathway involving OsNAP

Senescence-induced NAC (senNAC) TFs play a crucial role in senescence during the final stage of leaf development. In this study, we identified a rice senNAC, ONAC016, which functions as a positive regulator of leaf senescence. The expression of ONAC016 increased rapidly in rice leaves during the progression of dark-induced and natural senescence. The onac016-1 knockout mutant showed a delayed leaf yellowing phenotype, whereas the overexpression of ONAC016 accelerated leaf senescence. Notably, ONAC016 expression was upregulated by abscisic acid (ABA), and thus detached leaves of the onac016-1 mutant remained green much longer under ABA treatment. Quantitative RT-PCR analysis showed that ONAC016 upregulates the genes associated with chlorophyll degradation, senescence, and ABA signaling. Yeast one-hybrid and dual-luciferase assays revealed that ONAC016 binds directly to the promoter regions of OsNAP, a key gene involved in chlorophyll degradation and ABA-induced senescence. Taken together, these results suggest that ONAC016 plays an important role in promoting leaf senescence through the ABA signaling pathway involving OsNAP.

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.

Deletion of the sugar importer gene OsSWEET1b accelerates sugar starvation-promoted leaf senescence in rice.

Leaf senescence is a combined response of plant cells stimulated by internal and external signals. Sugars acting as signaling molecules or energy metabolites can influence the progression of leaf senescence. Both sugar starvation and accumulation can promote leaf senescence with diverse mechanisms that are reported in different species. Sugars Will Eventually be Exported Transporters (SWEETs) are proposed to play essential roles in sugar transport, but whether they have roles in senescence and the corresponding mechanism are unclear. Here, we functionally characterized a sugar transporter, OsSWEET1b, which transports sugar and promotes senescence in rice (Oryza sativa L.). OsSWEET1b could import glucose and galactose when heterologously expressed in Xenopus oocytes and translocate glucose and galactose from the extracellular apoplast into the intracellular cytosol in rice. Loss of function of OsSWEET1b decreased glucose and galactose accumulation in leaves. ossweet1b mutants showed accelerated leaf senescence under natural and dark-induced conditions. Exogenous application of glucose and galactose complemented the defect of OsSWEET1b deletion-promoted senescence. Moreover, the senescence-activated transcription factor OsWRKY53, acting as a transcriptional repressor, genetically functions upstream of OsSWEET1b to suppress its expression. OsWRKY53-overexpressing plants had attenuated sugar accumulation, exhibiting a similar phenotype as the ossweet1b mutants. Our findings demonstrate that OsWRKY53 downregulates OsSWEET1b to impair its influx transport activity, leading to compromised sugar accumulation in the cytosol of rice leaves where sugar starvation promotes leaf senescence.

Differential leaf flooding resilience in Arabidopsis thaliana is controlled by ethylene signaling-activated and age-dependent phosphorylation of ORESARA1

The phytohormone ethylene is a major regulator of plant adaptive responses to flooding. In flooded plant tissues, ethylene quickly increases to high concentrations owing to its low solubility and diffusion rates in water. Ethylene accumulation in submerged plant tissues makes it a reliable cue for triggering flood acclimation responses, including metabolic adjustments to cope with flood-induced hypoxia. However, persistent ethylene accumulation also accelerates leaf senescence. Stress-induced senescence hampers photosynthetic capacity and stress recovery. In submerged Arabidopsis, senescence follows a strict age-dependent pattern starting with the older leaves. Although mechanisms underlying ethylene-mediated senescence have been uncovered, it is unclear how submerged plants avoid indiscriminate breakdown of leaves despite high systemic ethylene accumulation. We demonstrate that although submergence triggers leaf-age-independent activation of ethylene signaling via EIN3 in Arabidopsis, senescence is initiated only in old leaves. EIN3 stabilization also leads to overall transcript and protein accumulation of the senescence-promoting transcription factor ORESARA1 (ORE1) in both old and young leaves during submergence. However, leaf-age-dependent senescence can be explained by ORE1 protein activation via phosphorylation specifically in old leaves, independent of the previously identified age-dependent control of ORE1 via miR164. A systematic analysis of the roles of the major flooding stress cues and signaling pathways shows that only the combination of ethylene and darkness is sufficient to mimic submergence-induced senescence involving ORE1 accumulation and phosphorylation. Hypoxia, most often associated with flooding stress in plants, appears to have no role in these processes. Our results reveal a mechanism by which plants regulate the speed and pattern of senescence during environmental stresses such as flooding. Age-dependent ORE1 activity ensures that older, expendable leaves are dismantled first, thus prolonging the life of younger leaves and meristematic tissues that are vital to whole-plant survival.