Delayed Leaf Senescence Research Articles

GhWRKY33 Interacts with GhTIFY10A to Synergistically Modulate Both Ageing and JA-Mediated Leaf Senescence in Arabidopsis.

WRKY transcription factors play critical roles in the modulation of transcriptional changes during leaf senescence, but the underlying mechanisms controlled by them in this progress still remain enigmatic. In this study, Gossypium hirsutum WRKY DNA-binding protein 33 (GhWRKY33) was characterized as a negative regulator of both ageing and JA-mediated leaf senescence. The overexpression of GhWRKY33 in Arabidopsis greatly delayed leaf senescence, as determined by elevated chlorophyll content, lower H2O2 content, and reduced expression of several senescence-associated genes (SAGs). An electrophoretic mobility shift assay (EMSA) and transient dual–luciferase reporter assay revealed that GhWRKY33 could bind to the promoters of both AtSAG12 and Ghcysp and suppress their expression. Yeast two-hybrid (Y2H) and firefly luciferase complementation imaging (LUC) assays showed that GhWRKY33 could interact with GhTIFY10A. Similarly, the overexpression of GhTIFY10A in Arabidopsis also dramatically delayed leaf senescence. Furthermore, both GhWRKY33 and GhTIFY10A negatively regulate JA-mediated leaf senescence. In addition, a transientdual-luciferase reporter assay indicated that GhWRKY33 and GhTIFY10A could function synergistically to inhibit the expression of both AtSAG12 and Ghcysp. Thus, our work suggested that GhWRKY33 may function as a negative regulator to modulate both ageing and JA-mediated leaf senescence and also contributes to a basis for further functional studies on cotton leaf senescence.

Grain-filling characteristics and yield formation of wheat in two different soil fertility fields in the Huang-Huai-Hai Plain.

Clarifying factors that underpinning the variation in wheat yield components between high and middle soil fertility fields is critical to increase grain production and narrow yield gap for smallholder farming systems in the Huang–Huai–Hai Plain (3HP), which characterized by a large variation in soil fertility. Two-year field experiments were conducted to investigate wheat tillering, leaf photosynthesis, and grain filling characteristics in different soil fertility fields: high soil fertility field (HF) and middle soil fertility field (MF). Results showed that the spike formation rate in HF was 12.7%–13.0% higher than that in MF, leading to an 18.0%–19.8% increase in spike number. In addition, HF improved canopy light interception and leaf photosynthesis characteristics after anthesis and delayed leaf senescence, contributing to the increase in both the active grain filling period and grain filling rate. This resulted in a higher 1,000 grain weight in HF, which was 8.2%–8.3% higher than that in MF. Compared to MF, HF obtained higher yields at 9,840 kg ha−1 in 2017/18 and 11,462 kg ha−1 in 2018/19, respectively. In summary, higher spike number and 1,000-grain weight, which were mediated by spike-formation rate, maximization of light interception and improved leaf photosynthesis. These results would have important implications for narrowing yield gap between MF and HF in the 3HP.

Overexpression of ZmIPT2 gene delays leaf senescence and improves grain yield in maize.

Cytokinins (CTKs) are a major phytohormone group that are significant in the promotion of cellular division, growth, and divergence. Isopentenyl transferase (IPT) regulates a rate-limiting step in plant CTK synthesis, promotes the synthesis of isopentenyl adenonucleotides from 5-AMP and isopentenyl pyrophosphate, and then converts both these chemicals into various CTKs. Here, the full-length cDNA of ZmIPT2, which encodes 322 amino acids, was isolated and was introduced into a maize inbred line by Agrobacterium-mediated transformation. In both controlled environments and field experiments, the overexpression of ZmIPT2 gene in the transformed plants delayed leaf senescence. Compared to the receptor line, the transgenic maize lines retained higher chlorophyll levels, photosynthetic rates, and cytokinin content for an extended period of time, and produced significantly higher grain yield by a margin of 17.71–20.29% under normal field planting conditions. Subsequently, ten possible genes that interacted with ZmIPT2 were analyzed by qRT-PCR, showing that the expression pattern of GRMZM2G022904 was consistent with ZmIPT2 expression. Through comprehensive analysis, we screened for transgenic lines with stable inheritance of ZmIPT2 gene, clear functional efficiency, and significant yield improvement, in order to provide theoretical basis and material support for the breeding of new high-yield transgenic maize varieties.

Delayed Leaf Senescence by Upregulation of Cytokinin Biosynthesis Specifically in Tomato Roots.

Cytokinins (CKs) regulate numerous plant developmental processes, including photosynthesis and leaf senescence. Isopentenyltransferase (IPT) is a rate-limiting enzyme in the CK-biosynthesis pathway. We overexpressed ipt under tissue-specific promoters to study the long-range effect of CK on the functioning of tomato source leaves. Photosynthetic activity over time provided the measure for leaf aging. Significantly delayed leaf senescence was observed in plants expressing ipt under a root-specific promoter, but not in those expressing the gene under a source leaf-specific promoter. The root-derived influence on leaf aging was further confirmed by grafting experiments. CK concentration in source leaves of both transgenic lines increased significantly, with different proportions of its various derivatives. On the other hand, root CK concentration was only slightly elevated. Nevertheless, the significant change in the proportion of CK derivatives in the root indicated that CK biosynthesis and metabolism were altered. Partial leaf defoliation upregulates photosynthetic rate in the remaining leaf; however, overexpression of ipt in either tissues eliminated this response. Interestingly, stem girdling also eliminated the photosynthetic response. Taken together, our findings suggest that leaf senescence is regulated by a CK-mediated root–shoot communication network. We propose that CK-mediated signal is translocated to the leaf via the xylem where it alters CK biosynthesis, resulting in delayed senescence.

The safflower bHLH transcription factor CtbHLH41 negatively regulates SA-induced leaf senescence through interaction with CtCP1

Salicylic acid (SA) plays an important role in regulating leaf senescence. However, the molecular mechanism of leaf senescence of safflower ( Carthamus tinctorius ) is still elusive. In this study, we found that the bHLH transcription factor (TF) CtbHLH41 in Carthamus tinctorius significantly delayed leaf senescence and inhibited the expression of senescence-related genes. In order to explore how CtbHLH41 promotes leaf senescence, we carried out yeast two-hybrid screening. In this study, by exploring the mechanism of CtbHLH41 regulating CtCP1 , it was found that CtCP1 promoted the hydrolysis of CtbHLH41 protein, accelerated the transcriptional activities of salicylic acid-mediated senescence-related genes CtSAG12 and CtSAG29 , chlorophyll degradation genes CtNYC1 and CtNYE1 , and accelerated leaf senescence. We found a negative SA regulator CtANS1 , which interacted with CtbHLH41 and regulated its stability, thereby inhibiting CtCP1 -mediated leaf senescence. In short, our results provide a new insight into the mechanism of CtbHLH41 actively regulating the senescence of safflower leaves induced by SA. • In the course of our research on CtbHLH41 , we found that the overexpression of CtbHLH41 slowed down leaf senescence. • CtCP1 was included in the results of CtbHLH41 screening by yeast two-hybrid, which may promote leaf senescence of plants. • We found that CtCP1 promoted the hydrolysis of CtbHLH41 protein and accelerated leaf senescence. • We also found a gene CtANS1 , which also interacts with CtbHLH41 , thereby delaying leaf senescence caused by CtCP1 .

A positive feedback regulatory loop, SA-AtNAP-SAG202/SARD1-ICS1-SA, in SA biosynthesis involved in leaf senescence but not defense response

Salicylic acid (SA) is an important plant hormone that regulates defense responses and leaf senescence. It is imperative to understand upstream factors that regulate genes of SA biosynthesis. SAG202/SARD1 is a key regulator for isochorismate synthase 1 (ICS1) induction and SA biosynthesis in defense responses. The regulatory mechanism of SA biosynthesis during leaf senescence is not well understood. Here we show that AtNAP, a senescence-specific NAC family transcription factor, directly regulates a senescence-associated gene named SAG202 as revealed in yeast one-hybrid and in planta assays. Inducible overexpreesion of AtNAP and SAG202 lead to high levels of SA and precocious senescence in leaves. Individual knockout mutants of sag202 and ics1 have markedly reduced SA levels and display a significantly delayed leaf senescence phenotype. Furthermore, SA positively feedback regulates AtNAP and SAG202. Our research has uncovered a unique positive feedback regulatory loop, SA-AtNAP-SAG202-ICS1-SA, that operates to control SA biosynthesis associated with leaf senescence but not defense response.

Melatonin mediates reactive oxygen species homeostasis via SlCV to regulate leaf senescence in tomato plants.

Melatonin (MT) functions in removing reactive oxygen species (ROS) and delaying plant senescence, thereby acting as an antioxidant; however, the molecular mechanism underlying the specific action of MT is unclear. Herein, we used the mutant plants carrying the MT decomposition gene melatonin 3-hydroxylase (M3H) in tomatoto elucidate the specific mechanism of action of MT. SlM3H-OE accelerated senescence by decreasing the content of endogenous MT in plants. SlM3H is a senescence-related gene that positively regulates aging. MT inhibited the expression of the senescence-related gene SlCV to scavenge ROS, induced stable chloroplast structure, and delayed leaf senescence. Simultaneously, MT weakened the interaction between SlCV and SlPsbO/SlCAT3, reduced ROS production in photosystem II, and promoted ROS elimination. In conclusion, MT regulates ROS homeostasis and delays leaf agingin tomato plants through SlCV expression modulation.

Physiological and transcription analyses reveal regulatory pathways of 6-benzylaminopurine delaying leaf senescence and maintaining quality in postharvest Chinese flowering cabbage

The regulatory role of cytokinins (CTKs) in leaf senescence has been documented in different species, including Chinese flowering cabbage. However, its physiological and molecular basis relatively remains unknown. In this study, exogenous application of a CTK analogue 6-benzylaminopurine (6-BA) significantly retarded leaf senescence of Chinese flowering cabbage, with less chlorophyll degradation and lower accumulation of reactive oxygen species (ROS) and malondialdehyde compared with the control group. Meanwhile, higher levels of soluble sugars and proteins, flavonoids, cellulose, amino acids, total phenols, procanthocyanins, and vitamin C were retained in 6-BA-treated leaves. 6-BA treatment also prevented the decline in endogenous CTK content and the increase in ethylene, abscisic acid, and jasmonic acid contents. Moreover, the comparative transcriptome analysis revealed that a total of 21,895 differently expressed genes (DEGs) were identified from four comparisons of 6-BA treatment versus the control during senescence. Further analysis showed that most of the identified DEGs were enriched in ROS, respiratory metabolism, and phytohormone pathways, and a total of 50 classes of transcription factors that were possibly involved in modulating these DEGs were obtained. The transcriptional levels of 18 DEGs were verified by Quantitative real-time PCR (qRT-PCR), which confirmed the accuracy of the transcriptomic data. Overall, these findings and data provide a comprehensive view of physiological and molecular events concerning with the CTK-mediated leaf senescence and -maintained quality in economical leafy vegetables.

Physiological and biochemical adaptive traits support the specific breeding of alfalfa (Medicago sativa) for severely drought‐stressed or moisture‐favourable environments

AbstractThe adaptation of alfalfa to moisture‐favourable and drought‐prone environments and its underlying mechanisms have not been thoroughly investigated despite their crucial importance to maximize the crop breeding progress. The main aim of this study was to support breeding strategies by exploring the relationship of leaf morphophysiological traits assessed in three growth chamber experiments with the adaptive response of five cultivars (Mamuntanas; Demnat 203; Erfoud 1; Prosementi; SARDI 10) that showed large genotype × environment interaction (GEI) across 10 drought‐prone to moisture‐favourable Mediterranean environments. Changes in shoot and root metabolite profiles across moisture‐contrasting conditions were assessed for two cultivars with contrasting adaptation pattern. The cultivar specifically adapted to drought‐prone environments (Mamuntanas), compared with that specifically adapted to moisture‐favourable environments (Demnat 203), displayed: (i) lower leaf wilting under drought stress; (ii) delayed leaf senescence under stress, assessed as limited chlorophyll reduction either in vivo from upper to central leaves or in vitro from control to polyethylene glycol‐treated leaflets, (iii) greater leaf tolerance to desiccation, measured in vitro as less pronounced reduction of leaf dry weight from control to polyethylene glycol‐treated leaflets, (iv) smaller leaves, (v) lower early root and shoot growth and (vi) lower leaf stomata density. The other cultivars exhibited different combinations and/or intermediate values of these traits. The metabolite profiles of Mamuntanas and Demnat 203 differed more in shoots than in roots. Mamuntanas accumulated more amino acids than Demnat 203 under moisture‐favourable and drought conditions. The distinct and partly incompatible combination of traits featuring the cultivars that maximized the crop yield in favourable or drought‐prone conditions (Mamuntanas and Demnat 203) improves our understanding of traits contributing to large GEI across moisture‐contrasting environments and support the breeding for specific adaptation to either condition. We identified a few inexpensive morphophysiological traits that could be used for early selection targeting drought‐prone environments.

Transcriptional Programs and Regulators Underlying Age-Dependent and Dark-Induced Senescence in Medicago truncatula.

In forage crops, age-dependent and stress-induced senescence reduces forage yield and quality. Therefore, delaying leaf senescence may be a way to improve forage yield and quality as well as plant resilience to stresses. Here, we used RNA-sequencing to determine the molecular bases of age-dependent and dark-induced leaf senescence in Medicago truncatula. We identified 6845 differentially expressed genes (DEGs) in M3 leaves associated with age-dependent leaf senescence. An even larger number (14219) of DEGs were associated with dark-induced senescence. Upregulated genes identified during age-dependent and dark-induced senescence were over-represented in oxidation–reduction processes and amino acid, carboxylic acid and chlorophyll catabolic processes. Dark-specific upregulated genes also over-represented autophagy, senescence and cell death. Mitochondrial functions were strongly inhibited by dark-treatment while these remained active during age-dependent senescence. Additionally, 391 DE transcription factors (TFs) belonging to various TF families were identified, including a core set of 74 TFs during age-dependent senescence while 759 DE TFs including a core set of 338 TFs were identified during dark-induced senescence. The heterologous expression of several senescence-induced TFs belonging to NAC, WKRY, bZIP, MYB and HD-zip TF families promoted senescence in tobacco leaves. This study revealed the dynamics of transcriptomic responses to age- and dark-induced senescence in M. truncatula and identified senescence-associated TFs that are attractive targets for future work to control senescence in forage legumes.

Understorey light quality affects leaf pigments and leaf phenology in different plant functional types.

Forest understorey plants receive most sunlight in springtime before canopy closure, and in autumn following leaf‐fall. We hypothesised that plant species must adjust their phenological and photoprotective strategies in response to large changes in the spectral composition of the sunlight they receive. Here, we identified how plant species growing in northern deciduous and evergreen forest understoreys differ in their response to blue light and ultraviolet (UV) radiation according to their functional strategy. We installed filters in a forest understorey in southern Finland, to create the following treatments attenuating: UV radiation below 350 nm, all UV radiation (< 400 nm), all blue light and UV radiation (< 500 nm), and a transparent control. In eight species, representing different functional strategies, we assessed leaf optical properties, phenology, and epidermal flavonoid contents over two years. Blue light accelerated leaf senescence in all species measured in the understorey, apart from Quercus robur seedlings, whereas UV radiation only accelerated leaf senescence in Acer platanoides seedlings. More light‐demanding species accumulated flavonols in response to seasonal changes in light quality compared to shade‐tolerant and wintergreen species and were particularly responsive to blue light. Reduction of blue and UV radiation under shade reveals an important role for microclimatic effects on autumn phenology and leaf photoprotection. An extension of canopy cover under climate change, and its associated suppression of understorey blue light and UV radiation, may delay leaf senescence for understorey species with an autumn niche.

CLE42 delays leaf senescence by antagonizing ethylene pathway in Arabidopsis.

Leaf senescence is the final stage of leaf development and is influenced by numerous internal and environmental factors. CLE family peptides are plant-specific peptide hormones that regulate various developmental processes. However, the role of CLE in regulating Arabidopsis leaf senescence remains unclear. Here, we found that CLE42 is a negative regulator of leaf senescence by using a CRISPR/Cas9-produced CLE mutant collection. The cle42 mutant displayed earlier senescence phenotypes, while overexpression of CLE42 delayed age-dependent and dark-induced leaf senescence. Moreover, application of the synthesized 12-amino-acid peptide (CLE42p) also delayed leaf senescence under natural and dark conditions. CLE42 and CLE41/44 displayed functional redundancy in leaf senescence, and the cle41 cle42 cle44 triple mutant displayed more pronounced earlier senescence phenotypes than any single mutant. Analysis of differentially expressed genes obtained by RNA-Seq methodology revealed that the ethylene pathway was suppressed by overexpressing CLE42. Moreover, CLE42 suppressed ethylene biosynthesis and thus promoted the protein accumulation of EBF, which in turn decreased the function of EIN3. Accordingly, mutation of EIN3/EIL1 or overexpression of EBF1 suppressed the earlier senescence phenotypes of the cle42 mutant. Together, our results reveal that the CLE peptide hormone regulates leaf senescence by communicating with the ethylene pathway.

Preharvest Hydrogen Peroxide Treatment Delays Leaf Senescence of Chinese Flowering Cabbage During Storage by Reducing Water Loss and Activating Antioxidant Defense System.

Leaf yellowing, an indicator of senescence, reduces commercial value of Chinese flowering cabbage after harvest. Hydrogen peroxide (H2O2) plays a dual role in mediating plant stress responses, but it is not clear whether and how it affects leaf senescence when exogenously stimulating the plants before harvest. Here, we found that preharvest application with low concentrations of H2O2 to root delays leaf senescence. Around 10 mM H2O2 reduced leaf yellowing rate by 8.2 and 26.4% relative to the control following 4 and 8 days storage, respectively. The H2O2-treated cabbages showed higher chlorophyll and lower relative expression of senescence-associated gene (SAG) BrSAG12 than the control. Proteomic analysis revealed 118 and 204 differentially expressed proteins (DEPs) in H2O2-treated plants at 4 and 8 days of storage, respectively. The main DEPs are involved in chlorophyll degradation and synthesis, water deprivation, antioxidant activity, and protections on chloroplast membranes. Decline of water loss in H2O2-treated cabbages was coincide with increase of proline contents and modulation of leaf stomatal aperture. Alleviation of oxidative stress was indicated by suppression of respiratory burst oxidase homolog and upregulation of reactive oxygen species (ROS) scavenging-related genes. These results were also supported by the alleviation of lipid peroxidation and the protections on cell integrity and photochemical efficiency in H2O2-treated group. Collectively, preharvest H2O2 treatment alleviates water loss and activates antioxidant defense system, protects chloroplast membrane from oxidative damage, and ultimately delays leaf senescence during storage. This study provides novel insights into the roles of H2O2 for regulating leaf senescence of Chinese flowering cabbage.

A new distinct geminivirus causes soybean stay-green disease

Plant viruses make up almost half of the plant disease-causing pathogens, affecting crop yields and the global economy (Savary et al., 2019). Soybean (Glycine max) is one of the most valuable legume crops in the world, supplying 25% of the global edible oil and two-thirds of the global concentrated protein for livestock feeding. Recently, the outbreak of soybean stay-green syndrome with delayed leaf senescence (stay-green), flat pods, and increased number of abnormal seeds has swept the soybean production in the Huang-Huai-Hai region of China, resulting in huge yield losses (Xu et al., 2019).

Delayed autumnal leaf senescence following nutrient fertilization results in altered nitrogen resorption.

Increased atmospheric nitrogen (N) deposition could create an imbalance between N and phosphorus (P), which may substantially impact ecosystem functioning. Changes in autumnal phenology (i.e., leaf senescence) and associated leaf nutrient resorption may profoundly impact plant fitness and productivity. However, we know little about how and to what extent nutrient addition affects leaf senescence in tree species, or how changes in senescence may influence resorption. We thus investigated the impacts of N and P addition on leaf senescence and leaf N resorption in 2-year-old larch (Larix principisrupprechtii) seedlings in northern China. Results showed that nutrient addition (i.e., N, P or N+P addition) significantly delayed autumnal leaf senescence, and decreased leaf N resorption efficiency (NRE) and proficiency (NRP), particularly in the N and N+P treatments. Improved leaf N concentrations were correlated with delayed leaf senescence, as indicated by the positive relationship between mature leaf N concentrations and the timing of leaf senescence. Following nutrient addition, larch seedlings shifted toward delayed onset, but more rapid, leaf senescence. Additionally, we observed an initial negative correlation between the timing of leaf senescence and NRE and NRP, followed by a positive correlation, indicating delayed and less efficient remobilization during the early stages of senescence, followed by accelerated resorption in the later stages. However, the latter effect was potentially impaired by the increased risk of early autumn frost damage, thus failed to fully compensate for the negative effects observed during the early stages of senescence. Improved soil P availability increased leaf N resorption and thus weakened the negative impact of delayed leaf senescence on leaf N resorption, so P addition had no significant impact on leaf N resorption. Overall, our findings clarify the relationship between nutrient addition-resorption and the linkage with leaf senescence, and would have important implications for plant nutrient conservation strategy and nutrient cycling.

Ecophysiology and Vegetative and Productive Behavior of 'Chardonnay' Vines under Protected Cultivation Systems in Serra Catarinense of Brazil

Aims: This study aimed to evaluate the effect of protected cultivation, with anti-hail screen or plastic cover, on phenological behavior, water potential, gas exchange, vegetative growth and vine production under protected cultivation systems in an altitude region of Santa Catarina.&#x0D; Place and Duration of Study: The experiment was carried out in São Joaquim, SC, in the 2018/19, 2019/20 and 2020/21 harvests, with the cultivar Chardonnay on Paulsen 1103 rootstock.&#x0D; Methodology: The treatments consist of an uncovered environment (control) and crops protected with white screen anti-hail (4 mm x 7 mm) and clear plastic raffia cover (160 µm).&#x0D; Results: The anti-hail net did not interfere in the phenological stages, photosynthesis and gas exchange of the plants and reduced the RFA, vegetative growth and production, in relation to the plastic cover, and similar development conditions to the control treatment (without cover). The plastic cover accelerated the maturation process, reduced photosynthetically active radiation (RFA), promoted vegetative growth, delayed leaf senescence and increased productivity about to plants without cover. The highest red to far red ratio was observed in an uncovered system. The light saturation point was higher in plants in the cultivation system protected with plastic cover. Plants under plastic cover showed an anticipation of fruit maturation about to the screen and without cover.

A long transcript mutant of the rubisco activase gene RCA upregulated by the transcription factor Ghd2 enhances drought tolerance in rice.

The transcription factor Ghd2 increases rice yield potential under normal conditions and accelerates leaf senescence under drought stress. However, its mechanism on the regulation of leaf senescence under drought stress remains unclear. In the present study, to unveil the mechanism, one target of Ghd2, the Rubisco activase gene RCA, was identified through the combined analysis of Ghd2-CRISPR transcriptome data and Ghd2-overexpression microarray data. Ghd2 binds to the 'CACA' motif in the RCA promoter by its CCT domain and upregulates RCA expression. RCA has alternative transcripts, RCAS and RCAL, which are predominantly expressed under normal conditions and drought stress, respectively. Similar to Ghd2-overexpressing plants, RCAL-overexpressing plants were more sensitive to drought stress than the wild-type. However, the plants overexpressing RCAS showed a weak drought-sensitive phenotype. Moreover, RCAL knockdown and knockout plants did not show yield loss under normal conditions, but exhibited enhanced drought tolerance and delayed leaf senescence. The chlorophyll content, the free amino acid content and the expression of senescence-related genes in the RCAL mutant were lower than those in the wild-type plants under drought stress. In summary, Ghd2 induces leaf senescence by upregulating RCAL expression under drought stress, and the RCAL mutant has important values in breeding drought-tolerant varieties.

Can deep fertilizer application enhance maize productivity by delaying leaf senescence and decreasing nitrate residue levels?

Deep fertilizer application is an effective strategy for minimizing gaseous losses and improving the nutrient use efficiency and grain yield. However, it is unclear whether deep fertilizer application can improve the antioxidant defense system in maize ( Zea mays L.) leaves and the photosynthetic capacity after silking to delay senescence, and then contribute to improvements in the yield and resource utilization efficiency. The effects on the NO 3 – -N residue levels also require elucidation. Therefore, we tested different fertilization application depths in the field during 2019–2020, where all of the N-P fertilizer was applied underground at 5 cm (D5), 15 cm (D15), 25 cm (D25), and 35 cm (D35) before sowing spring maize in the Loess Plateau region of China. The results showed that the antioxidant and photosynthetic performance of the leaves followed the order of: D25 > D15 > D5 > D35. The H 2 O 2 and O 2 – contents decreased by 2 1.5% and 14.0% under D25 compared with D5, respectively, and the net photosynthetic rate (Pn) and mean grain filling rate (G mean ) increased by 32.9% and 5.0%. The translocation and assimilation of nitrogen under D25 increased by 20.1% and 18.6% compared with D5, respectively, the translocation and assimilation of phosphorus increased by 43.6% and 54.3%, and the biomass and maize yield increased by 12.7% and 13.8%. The water use efficiency (23.5 kg·ha –1 ·mm –1 ), water productivity (45.7 kg ha –1 mm –1 ), nitrogen use efficiency (43.6%), and phosphorus use efficiency (20.3%) were significantly higher under D25 than the other treatments. The accumulated residual nitrate contents in the 0–100 cm soil layer were 6.0% and 8.0% lower under D15 and D25 than D5, respectively ( P < 0.05). However, D35 significantly increased the accumulated residual nitrate content in the 0–200 cm soil depth to increase the risk of leaching. A fertilization depth of 25 cm can delay maize leaf senescence and enhance the grain-filling capability by improving the antioxidant defense system and photosynthetic capacity of the leaves after silking, thereby increasing the maize yield and resource utilization efficiency. • Fertilization depth influenced spatial and temporal distribution of soil NO 3 – -N. • Leaf antioxidant defense system improved with appropriate fertilization depth. • Fertilization depth of 25 cm enhanced maize productivity and resource utilization. • Fertilization depth of 35 cm increased NO 3 – -N residue contents in 0–200 soil layer.

OsCOMT, encoding a caffeic acid O-methyltransferase in melatonin biosynthesis, increases rice grain yield through dual regulation of leaf senescence and vascular development.

SummaryMelatonin, a natural phytohormone in plants, plays multiple critical roles in plant growth and stress responses. Although melatonin biosynthesis‐related genes have been suggested to possess diverse biological functions, their roles and functional mechanisms in regulating rice grain yield remain largely unexplored. Here, we uncovered the roles of a caffeic acid O‐methyltransferase (OsCOMT) gene in mediating rice grain yield through dual regulation of leaf senescence and vascular development. In vitro and in vivo evidence revealed that OsCOMT is involved in melatonin biosynthesis. Transgenic assays suggested that OsCOMT significantly delays leaf senescence at the grain filling stage by inhibiting degradation of chlorophyll and chloroplast, which, in turn, improves photosynthesis efficiency. In addition, the number and size of vascular bundles in the culms and leaves were significantly increased in the OsCOMT‐overexpressing plants, while decreased in the knockout plants, suggesting that OsCOMT plays a positive role in vascular development of rice. Further evidence indicated that OsCOMT‐mediated vascular development might owe to the crosstalk between melatonin and cytokinin. More importantly, we found that OsCOMT is a positive regulator of grain yield, and overexpression of OsCOMT increase grain yield per plant even in a high‐yield variety background, suggesting that OsCOMT can be used as an important target for enhancing rice yield. Our findings shed novel insights into melatonin‐mediated leaf senescence and vascular development and provide a possible strategy for genetic improvement of rice grain yield.

The NAC factor LpNAL delays leaf senescence by repressing two chlorophyll catabolic genes in perennial ryegrass.

Expression of chlorophyll (Chl) catabolic genes during leaf senescence is tightly controlled at the transcriptional level. Here, we identified a NAC family transcription factor, LpNAL, involved in regulating Chl catabolic genes via the yeast one-hybrid system based on truncated promoter analysis of STAYGREEN (LpSGR) in perennial ryegrass (Lolium perenne L.). LpNAL was found to be a transcriptional repressor, directly repressing LpSGR as well as the Chl b reductase gene, NONYELLOWING COLORING1. Perennial ryegrass plants over-expressing LpNAL exhibited delayed leaf senescence or stay-green phenotypes, whereas knocking down LpNAL using RNA interference accelerated leaf senescence. Comparative transcriptome analysis of leaves at 30 d after emergence in wild-type, LpNAL-overexpression, and knock-down transgenic plants revealed that LpNAL-regulated stay-green phenotypes possess altered light reactions of photosynthesis, antioxidant metabolism, ABA and ethylene synthesis and signaling, and Chl catabolism. Collectively, the transcriptional repressor LpNAL targets both Chl a and Chl b catabolic genes and acts as a brake to fine-tune the rate of Chl degradation during leaf senescence in perennial ryegrass.