Leaf Senescence In Plants Research Articles

Mechanistic Insights into Leaf Senescence Regulation in Woody Plants: A Molecular Perspective.

Leaves, the primary carbon fixers in autotrophic plants, undergo a complex senescence process, which is critical for the redistribution of nutrients and supports ongoing growth and development. This natural aging phenomenon, often triggered at the end of a plant's life cycle or during the autumn season in perennial species, is finely regulated at multiple levels. Premature senescence can disrupt normal plant development, while the timing and pace of senescence significantly impact crop yield and quality. Notably, accelerated senescence under stress conditions may enhance the survival of future generations, suggesting an evolutionary strategy for plants to cope with harsh environments. Our review focuses on the molecular regulation of leaf senescence in woody plants, emphasizing the intricate determinants and regulatory mechanisms involved, including the role of phytohormones, environmental cues, and genetic factors. We highlight recent advances in understanding the regulation of leaf senescence in woody plants, integrating insights from multidisciplinary approaches and cutting-edge technologies.

Transcriptomic and metabolomic reveal OsCOI2 as the jasmonate-receptor master switch in rice root.

Jasmonate is an essential phytohormone involved in plant development and stress responses. Its perception occurs through the CORONATINE INSENSITIVE (COI) nuclear receptor allowing to target the Jasmonate-ZIM domain (JAZ) repressors for degradation by the 26S proteasome. Consequently, repressed transcription factors are released and expression of jasmonate responsive genes is induced. In rice, three OsCOI genes have been identified, OsCOI1a and the closely related OsCOI1b homolog, and OsCOI2. While the roles of OsCOI1a and OsCOI1b in plant defense and leaf senescence are well-established, the significance of OsCOI2 in plant development and jasmonate signaling has only emerged recently. To unravel the role of OsCOI2 in regulating jasmonate signaling, we examined the transcriptomic and metabolomic responses of jasmonate-treated rice lines mutated in both the OsCOI1a and OsCOI1b genes or OsCOI2. RNA-seq data highlight OsCOI2 as the primary driver of the extensive transcriptional reprogramming observed after a jasmonate challenge in rice roots. A series of transcription factors exhibiting an OsCOI2-dependent expression were identified, including those involved in root development or stress responses. OsCOI2-dependent expression was also observed for genes involved in specific processes or pathways such as cell-growth and secondary metabolite biosynthesis (phenylpropanoids and diterpene phytoalexins). Although functional redundancy exists between OsCOI1a/b and OsCOI2 in regulating some genes, oscoi2 plants generally exhibit a weaker response compared to oscoi1ab plants. Metabolic data revealed a shift from the primary metabolism to the secondary metabolism primarily governed by OsCOI2. Additionally, differential accumulation of oryzalexins was also observed in oscoi1ab and oscoi2 lines. These findings underscore the pivotal role of OsCOI2 in jasmonate signaling and suggest its involvement in the control of the growth-defense trade-off in rice.

Root-sourced H2O2 is essential for maintaining jasmonic acid and Na+/K+ homeostasis to delay leaf senescence during salt stress in Paspalum vaginatum

Improving salt tolerance and mitigating senescence in the presence of high salinity are crucial for sustaining agricultural productivity. Previous research has demonstrated that hydrogen peroxide (H2O2), specifically H2O2 derived from roots and mediated by the respiratory burst oxidase homolog (NADPH), plays a significant role in regulating ion and plant hormone homeostasis in glycophytic plants, such as Arabidopsis. However, the extent to which root-derived H2O2 fulfils similar functions in halophytic plants remains uncertain. Therefore, our study aimed to explore the potential contribution of root-sourced H2O2 in delaying leaf senescence induced by high salinity, utilizing seashore paspalum as a model halophytic plant. The application of the NADPH-oxidase inhibitor DPI, coupled with a series of leaf senescence analyses, we revealed that root-derived H2O2 significantly retards salt-induced leaf senescence. Furthermore, through the application of hormone analysis, lipidomics, ionomics, Non-invasive Micro-test Technology (NMT), and transcriptomics, we established that NADPH-dependent H2O2 induced by salt stress in the roots was indispensable for maintaining the balance of the aging hormone, jasmonic acid (JA), and sodium ion homeostasis within this halophytic plant. Finally, by utilizing AtrbohD Arabidopsis mutants and virus-induced gene silencing (VIGs) in Paspalum vaginatum, we demonstrated the pivotal role played by root-sourced H2O2 in upholding JA homeostasis and regulating JA-triggered leaf senescence in P. vaginatum. This study offers novel insights into the mechanisms that govern plant leaf senescence and its response to salinity-induced stress.

Arabidopsis GDH1 and GDH2 genes double knock-out results in a stay-green phenotype during dark-induced senescence.

Yellowing is the first visually observable sign of plant leaf senescence. We found that Arabidopsis double knockout mutant gdh1gdh2 for genes of NAD(H)-dependent glutamate dehydrogenase retains green color of the leaves (stay-green phenotype) during a dark-induced senescence, in contrast to wild-type plants, whose leaves turn yellow. When the gdh1gdh2 plants are exposed to the dark more than four days, they demonstrate slower chlorophyll degradation than in the wild-type plants under the same conditions, as well as dysregulation of chlorophyll breakdown genes encoding chlorophyll b reductase, Mg-dechelatase, pheophytinase and pheophorbide a oxygenase. The slowed degradation of chlorophyll b in gdh1gdh2 plants significantly alters the chlorophyll a/b ratio. Ion leakage in the mutant plants increases significantly from four to eight days in the darkness, correlating with their premature death during this period. The discovered facts suggest a functional connection between activity of NAD(H)-dependent glutamate dehydrogenase and dark-induced senescence progress in Arabidopsis.

Arabidopsis apoplast TET8 positively correlates to leaf senescence, and tet3tet8 double mutants are delayed in leaf senescence.

Extracellular vesicles (EVs) are membrane-bound exosomes secreted into the apoplast. Two distinct populations of EVs have been described in Arabidopsis: PEN1-associated and TET8-associated. We previously noted early leaf senescence in the pen1 single and pen1pen3 double mutant. Both PEN1 and PEN3 are abundant in EV proteomes suggesting that EVs might regulate leaf senescence in soil-grown plants. We observed that TET8 is more abundant in the apoplast of early senescing pen1 and pen1pen3 mutant rosettes and in older wild-type (WT) rosettes. The increase in apoplast TET8 in the pen1 mutant did not correspond to increased TET8 mRNA levels. In addition, apoplast TET8 was more abundant in the early leaf senescence myb59 mutant, meaning the increase in apoplast TET8 protein during leaf senescence is not dependent on pen1 or pen3. Genetic analysis showed a significant delay in leaf senescence in tet3tet8 double mutants after 6weeks of growth suggesting that these two tetraspanin paralogs operate additively and are positive regulators of leaf senescence. This is opposite of the effect of pen1 and pen1pen3 mutants that show early senescence and suggest PEN1 to be a negative regulator of leaf senescence. Our work provides initial support that apoplast-localized TET8 in combination with TET3 positively regulates age-related leaf senescence in soil-grown Arabidopsis plants.

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.

Phospholipase-mediated phosphate recycling during plant leaf senescence

BackgroundPhosphorus is a macronutrient necessary for plant growth and development and its availability and efficient use affect crop yields. Leaves are the largest tissue that uses phosphorus in plants, and membrane phospholipids are the main source of cellular phosphorus usage.ResultsHere we identify a key process for plant cellular phosphorus recycling mediated by membrane phospholipid hydrolysis during leaf senescence. Our results indicate that over 90% of lipid phosphorus, accounting for more than one-third of total cellular phosphorus, is recycled from senescent leaves before falling off the plants. Nonspecific phospholipase C4 (NPC4) and phospholipase Dζ2 (PLDζ2) are highly induced during leaf senescence, and knockouts of PLDζ2 and NPC4 decrease the loss of membrane phospholipids and delay leaf senescence. Conversely, overexpression of PLDζ2 and NPC4 accelerates the loss of phospholipids and leaf senescence, promoting phosphorus remobilization from senescent leaves to young tissues and plant growth. We also show that this phosphorus recycling process in senescent leaves mediated by membrane phospholipid hydrolysis is conserved in plants.ConclusionsThese results indicate that PLDζ2- and NPC4-mediated membrane phospholipid hydrolysis promotes phosphorus remobilization from senescent leaves to growing tissues and that the phospholipid hydrolysis-mediated phosphorus recycling improves phosphorus use efficiency in plants.

Tomato arabinosyltransferase prevents precocious senescence

Senescence, a crucial developmental process in the life cycle of plants, involves programmed destruction of cellular components of leaves. The onset of senescence is synchronized with other developmental processes for successful reproduction since senescence eventually leads to cell death. Arabinosyltransferase FASCIATED AND BRANCHED 2 (FAB2) is known to control meristem proliferation. Here, we show that FAB2 can inhibit premature leaf senescence in tomato plants. Both chemically mutagenized and CRISPR-generated fab2 mutants exhibited excessively accelerated senescence, which resulted in sterility. Transcriptome analysis revealed that FAB2 extended leaf longevity by suppressing transcription of genes highly expressed in mature leaves. Transcription of FAB2 was increased in younger leaves, potentially inhibiting premature leaf senescence. The precocious senescence of fab2 mutants was in contrast to fasciated inflorescence (fin) mutants, which carried mutations in a hydroxyproline O-arabinosyltransferase gene, leading to meristem overproliferation. Our observations indicate that complex genetic hierarchy in the cascade of tomato arabinosyltransferases could control different aspects of developmental processes such as stem cell proliferation and senescence.

Drier August and colder September slow down the delaying trend of leaf senescence in herbaceous plants on the Qinghai–Tibetan Plateau

Plant phenological shifts on the Qinghai–Tibetan Plateau (QTP) have gained considerable attention over the last few decades. However, temporal changes in plant autumn phenology and the main driving factors remain uncertain. Most previous studies used satellite-derived phenological transition dates and climatic statistics during the preseason, which have relatively large uncertainties and may mask some important climate change characteristics at the intra-annual scale, thus affecting exploration of the underlying phenological change causes. This study collected 1685 phenological records at 27 ground stations on the QTP during 1983–2017. Temporal change trends and break points in leaf senescence date (LSD) of 23 herbaceous species were assessed using least squares regression, a meta-analysis procedure, and the Pettitt test. The main drivers and causes were investigated through correlation analysis and contribution calculation based on LSD observations and monthly climatic data. Results showed that, LSD of QTP herbaceous plants was significantly delayed at a rate of 4.45 days/decade during 1983–2017. Break points were concentrated during 1999–2003, with an overall mean in 2001. After 2001, the delay trend in LSD decreased, falling from 5.26 days/decade to 2.54 days/decade. Air temperature and precipitation were the most important climatic factors that showed closer and more extensive correlations with LSD and greater contributions to the inter-annual variations in LSD. August and September were the most critical period during which climatic factors had higher contributions to the LSD shifts. However, August was drier, with precipitation significantly decreasing and temperature increasing, and September was colder after 2001. Therefore, the declining trend in LSD may be attributed to the drier August and colder September. This study has not only provided reliable field evidence on temporal changes in autumn phenology on the QTP, but has also provided valuable insights into autumn phenological modelling and regional carbon cycling in alpine regions.

Contrasting Effects of Grazing in Shaping the Seasonal Trajectory of Foliar Fungal Endophyte Communities on Two Semiarid Grassland Species.

Fungal endophytes are harboured in the leaves of every individual plant host and contribute to plant health, leaf senescence, and early decomposition. In grasslands, fungal endophytes and their hosts often coexist with large herbivores. However, the influence of grazing by large herbivores on foliar fungal endophyte communities remains largely unexplored. We conducted a long-term (18 yr) grazing experiment to explore the effects of grazing on the community composition and diversity of the foliar fungal endophytes of two perennial grassland species (i.e., Artemisia capillaris and Stipa bungeana) across one growing season. Grazing significantly increased the mean fungal alpha diversity of A. capillaris in the early season. In contrast, grazing significantly reduced the mean fungal alpha diversity of endophytic fungi of S. bungeana in the late season. Grazing, growing season, and their interactions concurrently structured the community composition of the foliar fungal endophytes of both plant species. However, growing season consistently outperformed grazing and environmental factors in shaping the community composition and diversity of both plant species. Overall, our findings demonstrate that the foliar endophytic fungal community diversity and composition differed in response to grazing between A. capillaris and S. bungeana during one growing season. The focus on this difference will enhance our understanding of grazing's impact on ecological systems and improve land management practices in grazing regions. This variation in the effects of leaf nutrients and plant community characteristics on foliar endophytic fungal community diversity and composition may have a pronounced impact on plant health and plant-fungal interactions.

PWL1, a G-type lectin receptor-like kinase, positively regulates leaf senescence and heat tolerance but negatively regulates resistance to Xanthomonas oryzae in rice.

Plant leaf senescence, caused by multiple internal and environmental factors, has an important impact on agricultural production. The lectin receptor-like kinase (LecRLK) family members participate in plant development and responses to biotic and abiotic stresses, but their roles in regulating leaf senescence remain elusive. Here, we identify and characterize a rice premature withered leaf 1 (pwl1) mutant, which exhibits premature leaf senescence throughout the plant life cycle. The pwl1 mutant displayed withered and whitish leaf tips, decreased chlorophyll content, and accelerated chloroplast degradation. Map-based cloning revealed an amino acid substitution (Gly412Arg) in LOC_Os03g62180 (PWL1) was responsible for the phenotypes of pwl1. The expression of PWL1 was detected in all tissues, but predominantly in tillering and mature leaves. PWL1 encodes a G-type LecRLK with active kinase and autophosphorylation activities. PWL1 is localized to the plasma membrane and can self-associate, mainly mediated by the plasminogen-apple-nematode (PAN) domain. Substitution of the PAN domain significantly diminished the self-interaction of PWL1. Moreover, the pwl1 mutant showed enhanced reactive oxygen species (ROS) accumulation, cell death, and severe DNA fragmentation. RNA sequencing analysis revealed that PWL1 was involved in the regulation of multiple biological processes, like carbon metabolism, ribosome, and peroxisome pathways. Meanwhile, interfering of biological processes induced by the PWL1 mutation also enhanced heat sensitivity and resistance to bacterial blight and bacterial leaf streak with excessive accumulation of ROS and impaired chloroplast development in rice. Natural variation analysis indicated more variations in indica varieties, and the vast majority of japonica varieties harbour the PWL1Hap1 allele. Together, our results suggest that PWL1, a member of LecRLKs, exerts multiple roles in regulating plant growth and development, heat-tolerance, and resistance to bacterial pathogens.

Arbuscular mycorrhizal symbiosis and melatonin synergistically suppress heat-induced leaf senescence involves in abscisic acid, gibberellin, and cytokinin-mediated pathways in perennial ryegrass

Leaf senescence is a prominent symptom of heat injury observed in cool-season plants. The application of melatonin (MT) and inoculation with mycorrhizal fungi can mitigate heat-induced leaf senescence. The current research aims to examine the individual and combined effects of arbuscular mycorrhizal (AM) inoculation and MT application on heat-related leaf senescence in perennial ryegrass (Lolium perenne L.). In addition, whether the effects of these treatments were in any way associated with abscisic acid (ABA), gibberellin (GA), and cytokinin (CTK) for exerting the bioactivity. According to the results, the suppression of heat-mediated leaf senescence using MT treatment and AM inoculation manifested as increased photosynthesis, turf quality (TQ), and plant growth, and reduced membrane lipid peroxidation levels as well as the chlorophyll catabolic genes (CCGs) and senescence-associated genes (LpSAG12.1 and Lph36) transcript levels in the heat-stressed plants. MT application and AM inoculation elevated the internal MT, GA, and CTK levels, while reducing the ABA levels in the heat-stressed plants. In addition, the MT biosynthesis genes (LpTDC1, LpTDC2, LpCOMT1, LpASMT1, and LpASMT3), the ABA catabolic gene, the GA biosynthesis genes, CTK biosynthesis genes, along with the associated signal transduction response transcription factors (TFs) (type-B ARRs) exhibited increased levels, whereas the expressions of the GA and CTK catabolic genes and the biosynthesis and signal transduction genes related to ABA exhibited decreased levels after MT application and AM inoculation in the heat-stressed plants. Furthermore, the application of exogenous MT notably elevated the AM colonization rate at high temperature (HT) condition. After 28 days of heat stress, compared to the treatment with neither AMF nor MT application, AM combined with MT achieved a synergistic effect, resulting in a 25.32%, 87.21%, 58.69%, 57.17%, and 28.46% increase in TQ, leaf chlorophyll content, net photosynthesis (Pn), leaf photochemical efficiency (Fv/Fm), and relative water content (RWC), respectively, in perennial ryegrass. Additionally, this treatment significantly reduced the electrolyte leakage (EL), hydrogen peroxide (H2O2) and malondialdehyde (MDA) levels by 30.76%, 38.19%, and 31.95%, respectively, and also significantly reduced the transcription levels of CCGs and senescence-associated genes. Consequently, it was inferred that a combination of AM and MT treatments promotes plant growth and development and suppresses heat-induced leaf senescence in plants.

OsDERF8 regulates rice leaf senescence through involvement in jasmonate signaling

Plant leaf senescence is regulated by complicated signaling network involving endogenous and environmental factors. Appropriate leaf senescence processing plays important roles in plant growth and stress response and contributes to crop production. The regulatory mechanism of leaf senescence has been widely investigated but still remains elusive. Here we identified the rice transcription factor OsDERF8 as the positive regulator of leaf senescence. Overexpression of OsDERF8 resulted in shortened reproductive stage and earlier leaf senescence, as well as lower grain yield. The knockout lines of OsDERF8 exhibited the “stay-green” phenotype and higher grain yield per plant. Dark induced senescence assays confirmed the function of OsDERF8 in senescence regulation. The leaves of OsDERF8 knockout lines showed less sensitivity to dark treatment with slighter chloroplast damage. OsDERF8 knockout mutants also exhibited less sensitivity to jasmonate (JA) treatment with higher chlorophyll accumulation and less root inhibition. Transcriptomic analysis and promoter-luciferase assays indicated that OsDERF8 regulated multiple senescence related genes, plant hormone related genes and photosynthesis genes. Taken together, OsDERF8 positively regulates rice leaf senescence through JA signaling and might be used for molecular breeding to increase grain yield.

Shade-Induced Leaf Senescence in Plants.

Leaf senescence is a vital developmental process that involves the orderly breakdown of macromolecules to transfer nutrients from mature leaves to emerging and reproductive organs. This process is essential for a plant's overall fitness. Multiple internal and external factors, such as leaf age, plant hormones, stresses, and light environment, regulate the onset and progression of leaf senescence. When plants grow close to each other or are shaded, it results in significant alterations in light quantity and quality, such as a decrease in photosynthetically active radiation (PAR), a drop in red/far-red light ratios, and a reduction in blue light fluence rate, which triggers premature leaf senescence. Recently, studies have identified various components involved in light, phytohormone, and other signaling pathways that regulate the leaf senescence process in response to shade. This review summarizes the current knowledge on the molecular mechanisms that control leaf senescence induced by shade.

Multiple factors induce temporal shifts in herbaceous plant leaf senescence dates on the Qinghai–Tibetan Plateau

Plant autumn phenology affects ecosystem carbon and water cycles. However, autumn phenological shifts of herbaceous plants and their primary regulators on the Qinghai–Tibetan Plateau (QTP) remain uncertain because previous studies were mainly based on remote sensing data. Studies using ground autumn phenological data observed at many stations are very few. This study explored the primary drivers of temporal shifts in leaf senescence date (LSD) and assessed the relative importance of climatic factors and spring phenophases to LSD shifts using correlation analysis, general linear regression, and partial least squares regression based on 1685 phenological records at 27 stations on the QTP. Results showed that, preseason total precipitation (PRE) and minimum air temperature (Tmin) had higher correlation coefficients with LSD and displayed more extensive importance in predicting LSD than other factors. Despite larger influences, contributions of PRE and Tmin to LSD inter-annual variations were only 14.9% and 14.2%, respectively. In total, PRE and air temperatures (TEMs) just explained 38.0% of LSD temporal shifts. These results indicate that although PRE and TEMs are the major regulators of LSD, temporal shifts in LSD are controlled by multiple factors. Overall, climatic factors and spring phenology contributed 53.7% and 15.6% to LSD variations, respectively, which means that climate change obviously outweighed spring phenology in driving LSD shifts. Our study revealed a critical role of PRE in regulating LSD shifts directly or indirectly by enhancing the sensitivity of LSD to TEMs. Moreover, we found that the impacts of precipitation change were more prominent on LSD of sedges than those of grasses and forbs. Therefore, we suggest that accurate autumn phenological models for plants on the QTP should include multiple factors and incorporate the influences of precipitation. This study can also provide insight into QTP grassland management from the perspective of phenological responses to climate change.

N6-methyladenosine (m6A) RNA modification as a metabolic switch between plant cell survival and death in leaf senescence.

Crop losses caused by climate change and various (a)biotic stressors negatively affect agriculture and crop production. Therefore, it is vital to develop a proper understanding of the complex response(s) to (a)biotic stresses and delineate them for each crop plant as a means to enable translational research. In plants, the improvement of crop quality by m6A editing is believed to be a promising strategy. As a reaction to environmental changes, m6A modification showed a high degree of sensitivity and complexity. We investigated differences in gene medleys between dark-induced leaf senescence (DILS) and developmental leaf senescence in barley, including inter alia RNA modifications active in DILS. The identified upregulated genes in DILS include RNA methyltransferases of different RNA types, embracing enzymes modifying mRNA, tRNA, and rRNA. We have defined a decisive moment in the DILS model which determines the point of no return, but the mechanism of its control is yet to be uncovered. This indicates the possibility of an unknown additional switch between cell survival and cell death. Discoveries of m6A RNA modification changes in certain RNA species in different stages of leaf senescence may uncover the role of such modifications in metabolic reprogramming. Nonetheless, there is no such data about the process of leaf senescence in plants. In this scope, the prospect of finding connections between the process of senescence and m6A modification of RNA in plants seems to be compelling.

DDG1 and G Protein α Subunit RGA1 Interaction Regulates Plant Height and Senescence in Rice (Oryza sativa)

Many studies have already shown that dwarfism and moderate delayed leaf senescence positively impact rice yield, but the underlying molecular mechanism of dwarfism and leaf senescence remains largely unknown. Here, using map-based cloning, we identified an allele of <i>DEP2</i>, <i>DDG1</i>, which controls plant height and leaf senescence in rice. The <i>ddg1</i> mutant displayed dwarfism, short panicles, and delayed leaf senescence. Compared with the wild-type, <i>ddg1</i> was insensitive to exogenous gibberellins (GA) and brassinolide (BR). <i>DDG1</i> is expressed in various organs, especially in stems and panicles. Yeast two-hybrid assay, bimolecular fluorescent complementation and luciferase complementation image assay showed that DDG1 interacts with the α-subunit of the heterotrimeric G protein. Disruption of <i>RGA1</i> resulted in dwarfism, short panicles, and darker-green leaves. Furthermore, we found that <i>ddg1</i> and the <i>RGA1</i> mutant was more sensitive to salt treatment, suggesting that DDG1 and RGA1 are involved in regulating salt stress response in rice. Our results show that DDG1/DEP2 regulates plant height and leaf senescence through interacting with RGA1.

Retardation of leaf senescence of aquatic plants using ascorbic acid

Potentiality of ascorbic acid on retardation of senescence was analysed using leaves of aquatic plant species namely Eichhornia crassipes and Jussiaea repens. Changes of some biochemical parameters like chlorophyll, protein as well as activity of catalase enzyme were analysed as reliable senescence indices during leaf senescence of the species under ambient ageing condition. With the progress of ageing duration from zero (0) to 96 hours the levels of chlorophyll and proteins in leaf discs gradually declined in both control and ascorbic acid treated samples. However, in the ascorbic acid treated samples the rate of decline was found to be much slower. The activity of the enzyme catalase was found to decrease progressively during the observation periods (0, 24, 48 and 96 hours) regardless of the treatment. Ascorbic acid partially alleviated the rapid fall of the enzyme activity during the ageing periods. Thus, ascorbic acid seems to be a potent senescence deferral agent for the experimental aquatic plant species

Overexpression of MsSAG113 gene promotes leaf senescence in alfalfa via participating in the hormone regulatory network.

Alfalfa (Medicago sativa) is a kind of high quality leguminous forage species, which was widely cultivated in the world. Leaf senescence is an essential process in plant development and life cycle. Here, we reported the isolation and functional analysis of an alfalfa SENESCENCE-ASSOCIATED GENE113 (MsSAG113), which belongs to the PP2C family and mainly plays a role in promoting plant senescence. In the study, Agrobacterium-mediated, gene expression analysis, next generation sequencing, DNA pull-down, yeast single hybridization and transient expression were used to identify the function of MsSAG113 gene. The MsSAG113 gene was isolated from alfalfa, and the transgenic plants were obtained by Agrobacterium-mediated method. Compared with the wildtype, transgenic plants showed premature senescence in leaves, especially when cultivated under dark conditions. Meanwhile, application of exogenous hormones ABA, SA, MeJA, obviously acclerated leaf senescence of transgenic plants. Furthermore, the detached leaves from transgenic plants turned yellow earlier with lower chlorophyll content. Transcriptome analysis identified a total of 1,392 differentially expressed genes (DEGs), involving 13 transcription factor families. Of which, 234 genes were related to phytohormone synthesis, metabolism and transduction. Pull-down assay and yeast one-hybrid assay confirmed that alfalfa zinc finger CCCH domain-containing protein 39 (MsC3H-39) could directly bind the upstream of MsSAG113 gene. In conclusion, the MsSAG113 gene plays a crucial role in promoting leaf senescence in alfalfa via participating in the hormone regulatory network. This provides an essential basis for further analysis on the regulatory network involving senescence-associated genes in alfalfa.

Genome-wide identification, phylogenetic, and expression analysis under abiotic stress conditions of Whirly (WHY) gene family in Medicago sativa L.

The WHY family is a group of plant-specific transcription factors, that can bind to single-stranded DNA molecules and play a variety of functions in plant nuclei and organelles, participating in the regulation of plant leaf senescence. It has been identified and analyzed in many species, however, the systematic identification and analysis of the WHY genes family have not yet been reported in alfalfa (Medicago sativa L.). Therefore, to explore the function of alfalfa the WHY genes, and 10 MsWHY genes were identified and further characterized their evolutionary relationship and expression patterns by analyzing the recently published genome of alfalfa. Comprehensive analysis of the chromosome location, physicochemical properties of the protein, evolutionary relationship, conserved motifs, and responses to abiotic stresses of the WHY gene family in alfalfa using bioinformatics methods. The results showed that 10 MsWHY genes were distributed on 10 chromosomes, and collinearity analysis showed that many MsWHYs might be derived from segmental duplications, and these genes are under purifying selection. Based on phylogenetic analyses, the WHY gene family of alfalfa can be divided into four subfamilies: I-IV subfamily, and approximately all the WHY genes within the same subfamily share similar gene structures. The 10 MsWHY gene family members contained 10 motifs, of which motif 2 and motif 4 are the conserved motifs shared by these genes. Furthermore, the analysis of cis-regulatory elements indicated that regulatory elements related to transcription, cell cycle, development, hormone, and stress response are abundant in the promoter sequence of the MsWHY genes. Real-time quantitative PCR demonstrated that MsWHYs gene expression is induced by drought, salt, and methyl jasmonate. The present study serves as a basic foundation for future functional studies on the alfalfa WHY family.