Chlorophyll Degradation Genes Research Articles

Effects of light and plant hormones on regreening in flavedos of Ponkan mandarin in vitro

In this study, the regulation of regreening in the flavedos of citrus fruit was investigated in vitro. The results showed blue light was much more effective than red light for inducing regreening in citrus fruit. In the blue light treatment, the up-regulation of chlorophyll biosynthetic genes and the down-regulation of chlorophyll degradation genes led to the re-accumulation of chlorophyll in the flavedos of mature fruit. In addition, we found that blue light was a necessary factor for GA-induced regreening in citrus fruit. Under blue light, GA treatment accelerated the re-accumulation of chlorophyll in the flavedos. In contrast to GA, ABA treatment did not induce regreening under blue light, and the flavedos kept in orange color. Compared with the blue light treatment alone, the contents of chlorophyll a, chlorophyll b, and total chlorophyll were decreased by the combination of ABA and blue light treatments. The results presented in this study suggested that blue light and GA are positive regulators for inducing regreening, while ABA is a negative regulator of regreening in the flavedo of mature citrus fruit.

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.

Ethylene accelerates maize leaf senescence in response to nitrogen deficiency by regulating chlorophyll metabolism and autophagy

Leaf senescence is an orderly and highly coordinated process, and finely regulated by ethylene and nitrogen (N), ultimately affecting grain yield and nitrogen-use efficiency (NUE). However, the underlying regulatory mechanisms on the crosstalk between ethylene- and N-regulated leaf senescence remain a mystery in maize. In this study, ethylene biosynthesis gene ZmACS7 overexpressing (OE-ZmACS7) plants were used to study the role of ethylene regulating leaf senescence in response to N deficiency, and they exhibited the premature leaf senescence accompanied by increased ethylene release, decreased chlorophyll content and Fv/Fm ratio, and accelerated chloroplast degradation. Then, we investigated the dynamics changes of transcriptome reprogramming underlying ethylene-accelerated leaf senescence in response to N deficiency. The differentially expressed genes (DEGs) involved in chlorophyll biosynthesis were significantly down-regulated, while DEGs involved in chlorophyll degradation and autophagy processes were significantly up-regulated, especially in OE-ZmACS7 plants in response to N deficiency. A gene regulatory network (GRN) was predicted during ethylene-accelerated leaf senescence in response to N deficiency. Three transcription factors (TFs) ZmHSF4, ZmbHLH106, and ZmEREB147 were identified as the key regulatory genes, which targeted chlorophyll biosynthesis gene ZmLES22, chlorophyll degradation gene ZmNYC1, and autophagy-related gene ZmATG5, respectively. Furthermore, ethylene signaling key genes might be located upstream of these TFs, generating the signaling cascade networks during ethylene-accelerated leaf senescence in response to N deficiency. Collectively, these findings improve our molecular knowledge of ethylene-accelerated maize leaf senescence in response to N deficiency, which is promising to improve NUE by manipulating the progress of leaf senescence in maize.

CsWRKY11 cooperates with CsNPR1 to regulate SA-triggered leaf de-greening and reactive oxygen species burst in cucumber

Salicylic acid (SA) is a multi-functional phytohormone, regulating diverse processes of plant growth and development, especially triggering plant immune responses and initiating leaf senescence. However, the early SA signaling events remain elusive in most plant species apart from Arabidopsis, and even less is known about the multi-facet mechanism underlying SA-regulated processes. Here, we report the identification of a novel regulatory module in cucumber, CsNPR1-CsWRKY11, which mediates the regulation of SA-promoted leaf senescence and ROS burst. Our analyses demonstrate that under SA treatment, CsNPR1 recruits CsWRKY11 to bind to the promoter of CsWRKY11 to activate its expression, thus amplifying the primary SA signal. Then, CsWRKY11 cooperates with CsNPR1 to directly regulate the expression of both chlorophyll degradation and ROS biosynthesis related genes, thereby inducing leaf de-greening and ROS burst. Our study provides a solid line of evidence that CsNPR1 and CsWRKY11 constitute a key module in SA signaling pathway in cucumber, and gains an insight into the interconnected regulation of SA-triggered processes.

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.

Tolerance of Forage Grass to Abiotic Stresses by Melatonin Application: Effects, Mechanisms, and Progresses

Climate change related abiotic stress has been potentially impacting the quantity and quality of forage grass. Melatonin, a multifunctional molecule that has been found to be present in all plants examined to date, plays a crucial role in improving forage grass tolerance to both biotic and abiotic stresses. However, research on melatonin’s role in forage grass is still developing. In this review, the effects of melatonin application on abiotic stress are the primary topic, and we try to find relative mechanisms. In order to determine whether melatonin has a good effect on forage grass, we compared and summarized the adapting ability of different forage grasses under abiotic stress after melatonin application in aspects of growth and development, photosynthesis, antioxidant systems, plant hormone interactions, and ion homeostasis. According to part of the data, we found that different forage grasses exhibited varying responses to endogenous melatonin content and exogenous melatonin dose applications. Meanwhile, the regulatory mechanisms of melatonin application include the expression of chlorophyll synthesis and degradation genes, electron transport and phosphorylation genes, stress regulation pathway genes, and plant hormone synthesis genes. We propose possible future studies that can further explore the metabolic pathways of melatonin and the molecular mechanisms of melatonin regulation of abiotic stress in forage grass. Specifically, research can focus on elucidating the signaling pathways, gene expression of regulatory networks, and interactions with other plant hormones. This will provide valuable theoretical and practical guidance for adapting to climate change and forage grass development.

Rice Basic Helix-Loop-Helix 079 (OsbHLH079) Delays Leaf Senescence by Attenuating ABA Signaling

Leaf senescence represents the final phase of leaf development and is characterized by a highly organized degenerative process involving the active translocation of nutrients from senescing leaves to growing tissues or storage organs. To date, a large number of senescence-associated transcription factors (sen-TFs) have been identified that regulate the initiation and progression of leaf senescence. Many of these TFs, including NAC (NAM/ATAF1/2/CUC2), WRKY, and MYB TFs, have been implicated in modulating the expression of downstream senescence-associated genes (SAGs) and chlorophyll degradation genes (CDGs) under the control of phytohormones. However, the involvement of basic helix-loop-helix (bHLH) TFs in leaf senescence has been less investigated. Here, we show that OsbHLH079 delays both natural senescence and dark-induced senescence: Overexpression of OsbHLH079 led to a stay-green phenotype, whereas osbhlh079 knockout mutation displayed accelerated leaf senescence. Similar to other sen-TFs, OsbHLH079 showed a gradual escalation in expression as leaves underwent senescence. During this process, the mRNA levels of SAGs and CDGs remained relatively low in OsbHLH079 overexpressors, but increased sharply in osbhlh079 mutants, suggesting that OsbHLH079 negatively regulates the transcription of SAGs and CDGs under senescence conditions. Additionally, we found that OsbHLH079 delays ABA-induced senescence. Subsequent RT-qPCR and dual-luciferase reporter assays revealed that OsbHLH079 downregulates the expression of ABA signaling genes, such as OsABF2, OsABF4, OsABI5, and OsNAP. Taken together, these results demonstrate that OsbHLH079 functions in delaying leaf yellowing by attenuating the ABA responses.

MiMYB10 transcription factor regulates biosynthesis and accumulation of carotenoid involved genes in mango fruit

Carotenoids are essential and beneficial substances for both plant and human health. Identifying the regulatory network of these pigments is necessary for improving fruit quality and commodity value. In this study, we performed integrative analyses of transcriptome data from two different type fruits, ripening peel color at green (‘Neelum’ mango) and red (‘Irwin’ mango). Specifically, we found that MiMYB10 transcription level was highly associated with mango peel color. Further, silencing MiMYB10 homologous gene in tomato fruits resulted in lower carotenoid and anthocyanin content. Electrophoretic mobility shift assays and dual-luciferase clarified that MiMYB10 regulates the carotenoid biosynthesis gene MiPDS (phytoene desaturase gene) in a direct manner. On the other hand, MiMYB10 activates the expression of carotenoid biosynthesis genes (PSY, Z-ISO, CRTISO, LCYE) and chlorophyll degradation gene (SGR1), promoting the accumulation of carotenoid, accelerating chlorophyll degradation, and controlling peel color. In summary, this study identified important roles of MiMYB10 in pigment regulatory and provided new options for breeding strategies aiming to improve fruit quality.

Comparative transcriptomic and plastid development analysis sheds light on the differential carotenoid accumulation in kiwifruit flesh.

Carotenoids are colorful lipophilic isoprenoids synthesized in all photosynthetic organisms which play roles in plant growth and development and provide numerous health benefits in the human diet (precursor of Vitamin A). The commercially popular kiwifruits are golden yellow-fleshed (Actinidia chinensis) and green fleshed (A. deliciosa) cultivars which have a high carotenoid concentration. Understanding the molecular mechanisms controlling the synthesis and sequestration of carotenoids in Actinidia species is key to increasing nutritional value of this crop via breeding. In this study we analyzed fruit with varying flesh color from three Actinidia species; orange-fleshed A. valvata (OF), yellow-fleshed A. polygama (YF) and green-fleshed A. arguta (GF). Microscopic analysis revealed that carotenoids accumulated in a crystalline form in YF and OF chromoplasts, with the size of crystals being bigger in OF compared to YF, which also contained globular substructures in the chromoplast. Metabolic profiles were investigated using ultra-performance liquid chromatography (UPLC), which showed that β-carotene was the predominant carotenoid in the OF and YF species, while lutein was the dominant carotenoid in the GF species. Global changes in gene expression were studied between OF and GF (both tetraploid) species using RNA-sequencing which showed higher expression levels of upstream carotenoid biosynthesis-related genes such as DXS, PSY, GGPPS, PDS, ZISO, and ZDS in OF species compared to GF. However, low expression of downstream pathway genes was observed in both species. Pathway regulatory genes (OR and OR-L), plastid morphology related genes (FIBRILLIN), chlorophyll degradation genes (SGR, SGR-L, RCCR, and NYC1) were upregulated in OF species compared to GF. This suggests chlorophyll degradation (primarily in the initial ripening stages) is accompanied by increased carotenoid production and localization in orange flesh tissue, a contrast from green flesh tissue. These results suggest a coordinated change in the carotenoid pathway, as well as changes in plastid type, are responsible for an orange phenotype in certain kiwifruit species.

Transcription factor CsMADS3 coordinately regulates chlorophyll and carotenoid pools in Citrus hesperidium.

Citrus, one of the largest fruit crops with global economic and nutritional importance, contains fruit known as hesperidium with unique morphological types. Citrus fruit ripening is accompanied by chlorophyll degradation and carotenoid biosynthesis, which are indispensably linked to color formation and the external appearance of citrus fruits. However, the transcriptional coordination of these metabolites during citrus fruit ripening remains unknown. Here, we identified the MADS-box transcription factor CsMADS3 in Citrus hesperidium that coordinates chlorophyll and carotenoid pools during fruit ripening. CsMADS3 is a nucleus-localized transcriptional activator, and its expression is induced during fruit development and coloration. Overexpression of CsMADS3 in citrus calli, tomato (Solanum lycopersicum), and citrus fruits enhanced carotenoid biosynthesis and upregulated carotenogenic genes while accelerating chlorophyll degradation and upregulating chlorophyll degradation genes. Conversely, the interference of CsMADS3 expression in citrus calli and fruits inhibited carotenoid biosynthesis and chlorophyll degradation and down-regulated the transcription of related genes. Further assays confirmed that CsMADS3 directly binds and activates the promoters of phytoene synthase 1 (CsPSY1) and chromoplast-specific lycopene β-cyclase (CsLCYb2), two key genes in the carotenoid biosynthetic pathway, and STAY-GREEN (CsSGR), a critical chlorophyll degradation gene, which explained the expression alterations of CsPSY1, CsLCYb2, and CsSGR in the above transgenic lines. These findings reveal the transcriptional coordination of chlorophyll and carotenoid pools in the unique hesperidium of Citrus and may contribute to citrus crop improvement.

Exogenous dopamine delays the senescence of detached Malus hupehensis leaves by reducing phytohormone signalling and sugar degradation

Leaf senescence is the ultimate stage in leaf development, accompanied by the degradation and redistribution of nutrients and biological macromolecules. Dopamine (DA), a type of catecholamine, plays a role in responding to various plant stresses through its strong antioxidant capacity. However, the relationship between DA and leaf senescence is poorly understood. Thus, leaves isolated from Malus hupehensis were treated with DA, and a dark-induced senescence experiment was conducted. We first found that 100 μmol L−1 DA was the optimal treatment for delaying leaf senescence. The leaves treated with 100 μmol L−1 DA showed higher chlorophyll content and Fv/Fm, and lower relative electrolyte leakage and malondialdehyde content during dark-induced senescence. DA was able to markedly decrease the expression of senescence associated genes (MdSAG12, MdSAG13, and MdSAG29) and a chlorophyll degradation gene (MdPAO). Compared with untreated leaves, the activity of antioxidant enzymes of leaves under DA treatment was significantly higher, and the level of reactive oxygen species (ROS) was significantly lower. Moreover, DA significantly reduced the content of phytohormones (1-aminocyclopropane-1-carboxylate acid, abscisic acid, salicylic acid, and jasmonic acid) that accelerate senescence during dark treatment and changed the expression of genes involved in phytohormone pathways to inhibit the transmission of signals. In addition, DA treatment significantly reduced the expression of genes related to the degradation of soluble sugar (fructose, glucose, sucrose, and sorbitol), thus significantly increasing the soluble sugar content relative to untreated leaves. Overall, our findings revealed that exogenous dopamine could decrease the expression of SAGs, improve the activity of antioxidant enzymes, reduce ROS levels, and the content of phytohormones that accelerate senescence and their signalling pathways, and decrease the degradation rate of soluble sugar to delay the senescence of apple leaves.

Exogenous melatonin ameliorates heat damages by regulating growth, photosynthetic efficiency and leaf ultrastructure of carnation

Carnation (Dianthus caryophyllus L.) is a floral crop that is highly valuable commercially. However, high temperatures adversely affect its growth and the quality of its cut flowers. Melatonin (MT) is a indole substance that can mitigate plant damage under heat stress. In this study, the leaves of carnation seedlings were sprayed with different concentrations of MT before exposure to high temperature. The indices of growth, physiological and chlorophyll fluorescence were measured and analyzed by the membership function method. The results showed that treatment with 100 μM MT was the most effective at ameliorating damage on carnation. We then analyzed the effects of 100 μM MT pretreatment on carnation at different time points of heat stress and found that this concentration of MT ameliorated the damage caused by heat stress, increased the content of photosynthetic pigments, enhanced the performance of photosystem II and improved photosynthesis. In addition, MT also reduced cell damage and lipid peroxidation, increased the activities of antioxidant enzymes and regulated the accumulation of osmotic substances in carnation. Moreover, MT increased the fresh/dry weight of stems and roots, promoted the opening of stomata, and protected the integrity of chloroplast structure of carnation. Compared with heat stress, pre-spraying with MT significantly down-regulated the transcription of a chlorophyll degradation gene and up-regulated the transcription of stress-related genes. Overall, this study provides a theoretical foundation for the mitigation of the adverse effects of exogenous MT under heat stress and proposes beneficial implications for the management of other plants subjected to global warming.

1-Methylcyclopropene retards pak choi (Brassica rapasubsp. chinensis) yellowing via BcNAC055-, BcMYB44-, and BcOBF1-mediated regulation of the key chlorophyll degrading geneBcNYC1during storage at 20 °C

AbstractThe objective of this study was to investigate the molecular regulatory mechanism of 1-methylcyclopropene (1-MCP) treatment on leaf yellowing of pak choi during storage at 20 °C. In the present study, compared with the control and 10 μL/L ethylene-treated pak choi, 5.0 μL/L 1-MCP fumigation alleviated the yellowing process of pak choi as proved by the maintenance of higher levels of colour, chlorophyll content, and appearance. 1-MCP treatment decreased chlorophyll breakdown by downregulating the activity of chlorophyll-degrading enzymes (chlorophyll b reductase (CBR) and pheophytinase (PPH)) and the expression of their related genes (BcNYC1 and BcPPH). The application of 1-MCP also inhibited the transcript abundance of ethylene biosynthesis and signal transduction genes (BcACO, BcEIN3, and BcERF) and reduced ethylene production, thus helping to maintain the green colour of pak choi; however, ethylene treatment exerted the opposite function. Meanwhile, three transcription factors (BcNAC055, BcMYB44, and BcOBF1) were successfully cloned. Experiments performed using yeast one-hybrid assay, dual-luciferase reporter system and in vivo bioluminescence imaging assay, confirmed that BcNAC055, BcMYB44, and BcOBF1 directly bound to the BcNYC1 promoter. 1-MCP inhibited the expression levels of BcNAC055, BcMYB44, BcOBF1, and BcNYC1 during storage, while the application of ethylene activated their expression. In conclusion, 1-MCP downregulated the expression of the key chlorophyll degradation gene BcNYC1 by inhibiting the transcript level of its three positive regulators (BcNAC055, BcMYB44, and BcOBF1) and lowered the activity of chlorophyll-degrading enzyme CBR, thereby helping mitigate chlorophyll breakdown to retard leaf yellowing in pak choi. The results of this work extend our understanding of 1-MCP-delayed yellowing in postharvest pak choi.

Transcriptome and Metabolome Analysis of a Late-Senescent Vegetable Soybean during Seed Development Provides New Insights into Degradation of Chlorophyll.

(1) Background: Senescence represents the final stage of plant growth and development, which transfers nutrients to growing seeds and directly affects the yield and quality of crops. However, little is known about chlorophyll degradation in developing and maturing seeds, in contrast to leaf senescence; (2) Methods: RNA-Seq was used to analyze the differentially expressed genes of different late-senescent germplasms. A widely untargeted metabolic analysis was used to analyze differential metabolites. In addition, qRT-PCR was conducted to detect gene expression levels; (3) Results: Transcriptome analysis revealed that ZX12 seeds have a higher expression level of the chlorophyll synthesis genes in the early stage of maturity, compared with ZX4, and have a lower expression level of chlorophyll degradation genes in the late stage of maturity. Flavonoids were the primary differential metabolites, and ZX12 contains the unique and highest expression of three types of metabolites, including farrerol-7-O-glucoside, cyanidin-3-o-(6'-o-feruloyl) glucoside, and kaempferide-3-o-(6'-malonyl) glucoside. Among them, farrerol-7-O-glucoside and cyanidin-3-o-(6'-o-feruloyl) glucoside are flavonoid derivatives containing mono and dihydroxy-B-ring chemical structures, respectively; and (4) Conclusions: It is speculated that the two metabolites can slow down the degradation process of chlorophyll by scavenging oxygen-free radicals in the chloroplast.

Ethylene Response Factor MaERF012 Modulates Fruit Ripening by Regulating Chlorophyll Degradation and Softening in Banana

Ethylene response factors (ERFs) are one of largest plant-specific transcription factor families involved in fruit ripening. However, the regulatory mechanism by which ERFs modulate fruit yellowing and softening remains unknown in banana. We previously found that the transcription of MaERF012 was closely related to 'Fenjiao' banana fruit ripening. Herein, we found that MaERF012 was differentially expressed in the fruit pulp and peel and was closely related to fruit ripening. MaERF012 activated the promoter activity of one chlorophyll degradation gene (MaSGR1), two starch degradation genes (MaGWD1 and MaAMY3), and three cell wall degradation genes (MaPL8, MaEXP-A8, and MaXYL23-like), which were tested by EMSA, Y1H, and DLR. Transient overexpression of MaERF012 accelerates fruit ripening by promoting fruit yellowing and softening by up-regulating the transcription of chlorophyll, starch, and cell wall degradation genes. Over-expression of MaERF012 alters the transcriptome profiles of the fruit peel and pulp, and the differentially expressed genes were mainly enriched in starch and sucrose metabolism, plant hormone signal transduction, biosynthesis of secondary metabolism, and fructose and mannose metabolism. Overall, the data showed that MaERF012 acts as a transcriptional activator by regulating fruit ripening by activating the transcription of chlorophyll, starch, and cell wall degradation genes.

The roles of Salvia miltiorrhiza-derived carbon dots involving in maintaining quality by delaying senescence of postharvest flowering Chinese cabbage

Salvia miltiorrhiza-derived carbon dots (SmCDs), as a new type of nanomaterial, play vital roles in plant growth, antioxidation and abiotic stress alleviation. Flowering Chinese cabbage is prone to wilt and yellowing after harvest. However, the roles of SmCDs in delaying senescence of postharvest flowering Chinese cabbage to maintain quality remain unclear. Herein, we found that SmCDs had effective impacts on anti-aging, enhancing maximal fluorescence ratio, procrastinating chlorophyll degradation, sustaining reactive oxygen species (ROS) metabolism homeostasis, and improving the contents of vitamin C, sucrose, soluble sugar, and flavonoid. Moreover, SmCDs suppressed the expressions of chlorophyll degradation genes (BrNYE1, BrNYC1, BrNOL, BrPPH, and BrPAO), senescence marker gene (BrSAG12), and respiratory burst oxidase homologs genes (BrRBohA, BrRBohB, BrRBohD, and BrRBohF), while SmCDs promoted the flavonoid biosynthesis genes (BrFLS3, BrFLS1, BrC4H, and BrCHI) expression. Interestingly, sucrose synthase, neutral invertase, and acid invertase might be the pivotal enzymes to restrict sugar accumulation under SmCDs treatment.

Oilseed rape MPK1 mediates reactive oxygen species-dependent cell death and jasmonic acid-induced leaf senescence

Leaf senescence is the terminal phase of leaf development, which involves remobilization of nutrients from leaves to other organs and is affected by many different endogenous (e.g. hormonal) and external stimuli. A proper control of leaf senescence is essential for fitness of annual plants. Although great progress has been made in identifying key genes or proteins controlling leaf senescence in Arabidopsis and several other plants, the relevant genes controlling leaf senescence in oilseed rape ( Brassica napus ) remain largely elusive. In this study, we found that a Mitogen-activated Protein Kinase, BnaMPK1 from oilseed rape positively modulated reactive oxygen species (ROS) -dependent cell death and jasmonic acid (JA)-induced leaf senescence. The expression of BnaMPK1 dramatically increased in senescing leaves of oilseed rape. Transient expression of BnaMPK1 in Nicotiana benthamiana and rapeseed protoplasts resulted in accumulation of ROS and cell death. Moreover, ectopic expression of BnaMPK1 in Arabidopsis exhibited accelerated JA-induced leaf senescence while atmpk1 mutants showed delayed leaf senescence. Furthermore, the expression of chlorophyll degradation and senescence marker genes Non-Yellowing 1 ( NYE1 , SGR1 ), Non-Yellow Coloring 1 ( NYC1 ), Senescence-Associated Gene 29 ( SAG29 ) and two well-known gene mediating JA-induced senescence ORESARA ( ORE ) 1 and ORE9 were induced in BnaMPK1 overexpression lines, whereas most of them were repressed in the atmpk1 mutant. A bimolecular fluorescence complementation (BiFC) and co-immunoprecipitation (Co-IP) assay revealed that BnaMKK3 interacted with BnaMPK1 and, constitutively active BnaMKK3 phosphorylated BnaMPK1 whereas inactive BnaMKK3 can not. Taken together, these results indicate that BnaMPK1 acts as a positive regulator of ROS- and JA-dependent leaf senescence. • BnaMPK1 expression level is up-regulated in senescing leaves. • BnaMPK1 expression induces ROS-dependent cell death in leaves and protoplasts of oilseed rape. • BnaMPK1 modulates jasmonic acid (JA)-induced leaf senescence. • BnaMPK1 expression induces the transcription of a few senescence-associated marker genes. • BnaMPK1 interacts with upstream BnaMKK3 and is phosphorylated by BnaMKK3.

Elevated CO2 delayed yellowing by maintaining chlorophyll biosynthesis and inhibiting chlorophyll degradation and carotenoid accumulation of postharvest broccoli

Yellowing is always accompanied by chlorophyll degradation and carotenoid accumulation, which is an important indicator for evaluating the quality and commercial value of postharvest broccoli. Elevated CO2 treatment was applied in broccoli heads to investigate its effect and mechanism on pigment metabolism. The results demonstrated that 30% CO2 treatment maintained higher nutritional quality by increasing phenols and flavonoids contents and delayed the yellowing by alleviating chlorophyll loss and carotenoid accumulation. The chlorophyll molecule could also be continuously synthesized in postharvest broccoli. The up-regulation of chlorophyll synthesis genes (BoMCase, BoChlM, BoChlE, BoPOR, BoDVR and BoChlG) and chlorophyll combination genes (BoCAB1 and BoCAB2) and the down-regulation of chlorophyll degradation genes (BoSGR1, BoNYC1, BoPPH, BoPAO and BoRCCR) were observed in postharvest broccoli treated with 30% CO2. Additionally, 30% CO2 treatment down-regulated the expression of BoPSY, BoLCYB, BoCHYB and BoVDE, thereby inhibiting zeaxanthin and β-carotene biosynthesis. This study provided new insights into chlorophyll biosynthesis after harvest and the regulation of elevated CO2 on pigment metabolism in postharvest broccoli.

Chlorine dioxide alleviates the yellowing process of broccoli by regulating chlorophyll degrading enzyme activity and gene expression

During the postharvest storage of broccoli, yellowing becomes a problem that affects the nutritional value and market value of broccoli. The aim of this study was to investigate the effect of chlorine dioxide (ClO2) on chlorophyll degradation in postharvest broccoli. Broccoli heads were immersed in 100 mg L−1 ClO2 solution and then stored at 4°C for 25 days. The results showed that postharvest ClO2 treatment delayed the yellowing of broccoli, suppressed weight loss and relative electrical conductivity, and increased total soluble solid content, indicating that ClO2 treatment could delay the decline of broccoli quality. At the same time, ClO2 treatment also reduced the loss of chlorophyll content and suppressed chlorophyllase (CLH), pheophyllase (PPH) and pheophyllase a oxygenase (PAO) activity, which in turn inhibited the expression of BoCLH1, BoCLH2, BoCLH3, BoPPH, and BoPAO. In summary, the results indicated that ClO2 treatment could delay the yellowing rate and maintain the commercial value of broccoli during storage. Novelty impact statement Chlorine dioxide (ClO2) treatment can delay yellowing and maintain the commercial value of broccoli. ClO2 treatment inhibited chlorophyll degrading enzyme activity in harvested broccoli. ClO2 treatment can downregulate the expression of chlorophyll degradation gene in harvested broccoli.

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 .