Chlorophyll Catabolism Research Articles

NAC Transcription Factor PpNAP4 Promotes Chlorophyll Degradation and Anthocyanin Synthesis in the Skin of Peach Fruit.

Chlorophyll (Chl) catabolism and anthocyanin synthesis play pivotal roles in determining the final skin color of fruits during maturation. However, in peach (Prunus persica) fruit, the regulatory mechanism governing skin color, especially the Chl catabolism, remains largely elusive. In this study, we identified ten Chl catabolic genes (CCGs), with PpSGR emerging as a key regulator in Chl degradation in peaches. Furthermore, a NAC-like, activated by AP3/P1 (NAP) transcription factor (TF), PpNAP4, was identified as a positive modulator of Chl breakdown. PpNAP4 induced the expression of PpSGR and other CCGs, including PpPPH, PpPAO, and PpTIC55-2, by directly binding to their promoters. Overexpression of PpNAP4 resulted in a heightened expression of these genes and accelerated Chl degradation. Notably, PpNAP4 also positively regulated the expression of PpANS and PpMYB10.1, one key structural gene and a core transcriptional regulator of anthocyanin synthesis, thereby contributing to fruit coloration. In summary, our findings elucidate that PpNAP4 serves as a pivotal regulator in determining the final skin color of peach by orchestrating Chl degradation and anthocyanin accumulation through direct activation of multiple CCGs and anthocyanin related genes.

Regulation of skin pigments in winter jujube fruit treated with elevated O2

Color deterioration is one of the major symptoms of postharvest senescence in winter jujube fruit. Elevated O2 (60 %) was applied to winter jujube fruit during storage at 0 °C and 90 % relative humidity. The changes in three major skin pigments, chlorophyll, carotenoid, and anthocyanin, were quantified to explain changes in skin color. The results showed that elevated O2 maintained the contents of chlorophyll and carotenoid during the initial stages of storage, which were 25 % higher chlorophyll a, 34 % higher chlorophyll b, and 18 % higher carotenoid compared to the control on day 7. The maintenance of chlorophyll content under elevated O2 was due to the inhibition of chlorophyll catabolism. Additionally, elevated O2 treatment also maintained carotenoid content by activating its biosynthesis rather than inhibiting its degradation. During the later stages of storage, the accumulation of anthocyanin was enhanced by elevated O2, with a 1.3-fold increase in anthocyanin observed in elevated O2-treated fruit compared to the control fruit on day 21. Elevated O2 treatment effectively activated phenylpropanoid biosynthesis and flavonoid biosynthesis pathways, leading to the accumulation of anthocyanin. This study elucidated the mechanism by which elevated O2 regulated color deterioration in winter jujube fruit.

Graph-Based Pangenome of Actinidia chinensis Reveals Structural Variations Mediating Fruit Degreening.

Fruit ripening is associated with the degreening process (loss of chlorophyll) that occurs in most fruit species. Kiwifruit is one of the special species whose fruits may maintain green flesh by accumulating a large amount of chlorophyll even after ripening. However, little is known about the genetic variations related to the fruit degreening process. Here, a graph-based kiwifruit pangenome by analyzing 14 chromosome-scale haplotype-resolved genome assemblies from seven representative cultivars or lines in Actinidia chinensis is built. A total of 49,770 non-redundant gene families are identified, with core genes constituting 46.6%, and dispensable genes constituting 53.4%. A total of 84,591 non-redundant structural variations (SVs) are identified. The pangenome graph integrating both reference genome sequences and variant information facilitates the identification of SVs related to fruit color. The SV in the promoter of the AcBCM gene determines its high expression in the late developmental stage of fruits, which causes chlorophyll accumulation in the green-flesh fruits by post-translationally regulating AcSGR2, a key enzyme of chlorophyll catabolism. Taken together, a high-quality pangenome is constructed, unraveled numerous genetic variations, and identified a novel SV mediating fruit coloration and fruit quality, providing valuable information for further investigating genome evolution and domestication, QTL genes function, and genomics-assisted breeding.

Involvement of BcERF109 in 1-MCP-delayed yellowing of pak choi (Brassica rapa subsp. Chinensis) via mitigation of major chlorophyll-degrading gene expression during storage

Leaf yellowing is a typical senescence symptom in postharvest pak choi (Brassica rapa subsp. Chinensis). Ethylene response factors (ERFs) are considered important regulators of leaf senescence. This study explored the likely regulatory effects of BcERF on pak choi yellowing via 1-methylcyclopropene (1-MCP) treatments. We identified an ERF transcription factor (TF), BcERF109, which may be involved in ethylene-induced pak choi yellowing. Treatment with 5.0 µL L–1 1-MCP suppressed the transcripts of chlorophyll catabolism genes (BcPPH1, BcRCCR, BcSGR2, and BcNYC1), inhibited decreases in chlorophyll content and chlorophyll fluorescence parameters, delayed chloroplast disintegration, and eventually mitigated yellowing. The treatment also blocked ethylene production and impeded the activities and transcripts of ethylene synthesis enzymes (ACC oxidase [ACO] and 1-aminocyclopropene-1-carboxylate [ACC] synthase [ACS]). In contrast, treatment with 10.0 µL L–1 ethylene accelerated pak choi yellowing, as indicated by greater ethylene production, activities and transcripts of ACO and ACS, and expression of chlorophyll catabolism genes, as well as reductions in chlorophyll content and fluorescence parameters. BcERF109 was identified as a nuclear-localised protein; its transcription levels were downregulated by 1-MCP and upregulated by ethylene. Molecular biology assays revealed that BcERF109 enhanced the transcriptional capacities of BcPPH1, BcRCCR, BcNYC1, and BcSGR2 by binding to their promoters. The transient overexpressing of BcERF109 in tobacco leaves stimulated the expression of endogenous genes (BcPPH1, BcRCCR, BcNYC1, BcSGR2, and BcERF109), leading to accelerated chlorophyll degradation and leaf yellowing. The application of 1-MCP mitigated pak choi yellowing by influencing ethylene synthesis and modulating the regulatory effects of BcERF019 on genes associated with chlorophyll catabolism. These results revealed a new regulatory mechanism involving ERF TFs in 1-MCP-induced delayed yellowing of green vegetables.

E3 ubiquitin ligase MaRZF1 modulates high temperature-induced green ripening of banana by degrading MaSGR1.

High temperatures (>24°C) prevent the development of a yellow peel on bananas called green ripening, owing to the inhibition of chlorophyll degradation. This phenomenon greatly reduces the marketability of banana fruit, but the mechanisms underlining high temperature-repressed chlorophyll catabolism need to be elucidated. Herein, we found that the protein accumulation of chlorophyll catabolic enzyme MaSGR1 (STAY-GREEN 1) was reduced when bananas ripened at high temperature. Transiently expressing MaSGR1 in banana peel showed its positive involvement in promoting chlorophyll degradation under high temperature, thereby weakening green ripening phenotype. Using yeast two-hybrid screening, we identified a RING-type E3 ubiquitin ligase, MaRZF1 (RING Zinc Finger 1), as a putative MaSGR1-interacting protein. MaRZF1 interacts with and targets MaSGR1 for ubiquitination and degradation via the proteasome pathway. Moreover, upregulating MaRZF1 inhibited chlorophyll degradation, and attenuated MaSGR1-promoted chlorophyll degradation in bananas during green ripening, indicating that MaRZF1 negatively regulates chlorophyll catabolism via the degradation of MaSGR1. Taken together, MaRZF1 and MaSGR1 form a regulatory module to mediate chlorophyll degradation associated with high temperature-induced green ripening in bananas. Therefore, our findings expand the understanding of posttranslational regulatory mechanisms of temperature stress-caused fruit quality deterioration.

Phenylalanine maintains the postharvest quality of ‘Jinfeng’ pear fruit by modulating the tricarboxylic acid cycle and chlorophyll catabolism

Quality breakdown caused by high respiration, evaporation, and pigment degradation affects the storage ability and shelf life of pear fruit. Phenylalanine is an aromatic amino acid that can enhance the nutritional quality and disease resistance of vegetables and fruit. This study was conducted to assess the effects of exogenous phenylalanine on quality indicators, tricarboxylic acid (TCA) cycle, and chlorophyll catabolism of ‘Jinfeng’ pear fruit. Results showed that phenylalanine treatment declined a* value, b* value, ΔE, and malondialdehyde content, enhanced L* value, soluble solids and ascorbic acid contents, and titratable acidity, but delayed the decrease of flesh firmness. Phenylalanine also reduced pyruvate dehydrogenase, isocitrate dehydrogenase, aconitase, citrate synthase, fumarase, succinate dehydrogenase, and malate dehydrogenase activities and gene expressions as well as PcNADP-ME expression and α-keto glutaric dehydrogenase (α-KGDH) activity in the TCA cycle of pears. Moreover, phenylalanine suppressed the expression levels of PcNCY1, PcHCAR, PcCHL1, PcPAO, PcRCCR, PcPPH, and PcSGR1/2 in chlorophyll degradation. Meanwhile, phenylalanine treatment enhanced malic acid, citric acid, succinic acid, total chlorophyll, chlorophyll a, and chlorophyll b contents in pears. These results indicate that exogenous phenylalanine could keep the quality of pears after harvest by inhibiting the key gene expression and enzyme activity in the TCA cycle and chlorophyll degradation. These findings also suggest that phenylalanine can be used as a potential inducer to delay yellowing and maintain the postharvest quality of fruit.

Preharvest Application of Sodium Nitroprusside Alleviates Yellowing of Chinese Flowering Cabbage via Modulating Chlorophyll Metabolism and Suppressing ROS Accumulation.

Chinese flowering cabbage is prone to senescence and yellowing after harvest, leading to a huge postharvest loss. Nitric oxide (NO) is a multifunctional plant growth regulator, but the effect of preharvest application of NO on the storage quality of Chinese flowering cabbage remains unclear. Preharvest application of 50 mg L-1 sodium nitroprusside (SNP, a NO donor) to the roots obviously reduced leaf yellowing in Chinese flowering cabbage during storage. Proteomic analysis reveals 198 differentially expressed proteins (DEPs) in SNP-treated plants compared to the control. The main DEPs were significantly enriched in chlorophyll metabolisms, phenylpropanoid synthesis, and antioxidant pathways. SNP treatment enhanced chlorophyll biosynthesis and suppressed chlorophyll-degradation-related proteins and genes. It also modulated flavonoid-biosynthesis-related genes, and 21 significantly regulated flavonoids were identified in SNP-treated plants. The enhanced antioxidant capacity in SNP-treated plants was able to decrease chlorophyll catabolism by inhibiting peroxidase-mediated chlorophyll bleaching. Collectively, preharvest SNP treatment modulated chlorophyll metabolism and preserved chlorophyll content in leaves during storage. Moreover, SNP treatment enhanced flavonoid synthesis, suppressed reactive oxygen species accumulation, and delayed the senescence process, thereby maintaining leaf greening in Chinese flowering cabbage. These findings highlight the role of exogenous NO in alleviating yellowing of leafy vegetables.

Black bean aphid populations and chlorophyll composition changes as responses of guelder rose to aphid infestation stress conditions

Aphis fabae Scop. is phloem-feeding insect that cause substantial damage to horticulare and agriculture worldwide due to feeding – related damage and the transmission of economically important plant viruses. These aphids cause a detrimental effects in attacked organs, like depletion of photoassimilates. Insect feeding can among others reduced chlorophyll catabolism. In the present investigations we determined the chlorophyll a and b levels (SPAD readings) in uninfested leaves and in Aphis fabae-infested leaves of Viburnum opulus shrubs, wild plants and garden variety, which were grown in green areas around Siedlce, east central Poland. Feeding by A. fabae affected chlorophyll a + b level. The insect feeding reduces the concentration of photosynthetic pigment in the infested shrubs. The level of chlorophyll in plants occupied by aphids was clearly lower than the level in plants where aphids were not found. We also found that chlorophyll levels increased with the progress of growing season, the level of chlorophyll differed between date of survey, being higher for the latest survey (mid-June) and that the place where the plant is located is important, wild V. opulus have slightly more level of chlorophyll compared to garden ones. Chlorophyll level might be useful as an indicator of plant responses to aphid damage.

Insights into profiling of p-coumaric acid treatment on delaying the yellowing of broccoli

Postharvest yellowing is a prominent problem in the broccoli industry. Here, we investigated the impact of p-coumaric acid (p-CA) treatment on the sensory quality of broccoli during shelf life. The 0.5 mmol L−1p-CA treatment delayed yellowing, as indicated by higher -a/b (chromaticity value), fluorescence decline ratio, and maximum quantum yield value, as well as lower levels of yellowing index. Meanwhile, chlorophyll content in the treated group was higher compared to the control, due to the restriction of p-CA treatment on the increase of chlorophyll-degrading enzyme activities. The inhibition of up-regulated expression of genes involved in chlorophyll catabolism following p-CA treatment supported the above argument. Additionally, treatment improved the activities of antioxidant enzymes and total phenol concentration to impede the accumulation of malondialdehyde and superoxide anion, alleviating oxidative damage. Statistical analysis further proved that p-CA treatment reduced chlorophyll degradation and enhanced antioxidant capacity as the mechanism to delay yellowing.

Photosensitization dermatitis in animals

Photosensitization, also known as photodermatitis, is an abnormal reaction of the skin when exposed to light and is caused by accumulation of photosensitizing substances in the skin, resulting in a severe dermatitis of the skin unprotected by unpigmented. There are three types of photosensitization: (a) primary, in which photodynamic chemicals, or plant toxins, reach the skin through the circulation, (b) congenital porphyria, in which there is a metabolic, congenital defect in porphyrin metabolism, and (c) secondary (hepatogenous), which occurs when the capacity of the liver to excrete derived from the catabolism of alimentary chlorophyll is impaired. We consider that liver pathologies are the most important in animals from Romania.

Melatonin delays leaf senescence in pak choi (Brassica rapa subsp. chinensis) by regulating biosynthesis of the second messenger cGMP

Melatonin (MT) is a low molecular weight compound with multiple biological functions in plants. It is known to delay leaf senescence in various species. However, no data are available on the MT signaling pathway in postharvest vegetables. This study demonstrates that MT increases cGMP concentration and the expression of the cGMP synthesis gene BcGC1 in pak choi. The cGMP inhibitor LY83583 destroys effect of MT delaying the leaf senescence. LY83583 also prevents MT treatment from reducing the expression of chlorophyll metabolism-related genes (BcNYC1, BcNOL, BcPPH1/2, BcSGR1/2, and BcPAO) and senescence genes (BcSAG12 and BcSAG21). It also inhibits MT from reducing the activity of the key chlorophyll catabolism enzymes Mg-dechelatase, pheophytinase, and pheide a oxygenase. Thus, the ability of MT to maintain high levels of chlorophyll metabolites is also destroyed. The Arabidopsis cGMP synthetic gene mutant atgc1 was used to confirm that delayed leaf senescence caused by MT is mediated, at least in part, by the second messenger cGMP.

Jasmonate signaling controls negative and positive effectors of salt stress tolerance in rice.

Plant responses to salt exposure involve large reconfiguration of hormonal pathways that orchestrate physiological changes towards tolerance. Jasmonate (JA) hormones are essential to withstand biotic and abiotic assaults, but their roles in salt tolerance remain unclear. Here we describe the dynamics of JA metabolism and signaling in root and leaf of rice, a plant species that is highly exposed and sensitive to salt. Roots activate the JA pathway in an early pulse, while 2 nd leaf displays a biphasic JA response with peaks at 1 hour and 3 days post-exposure. Based on higher salt tolerance of a rice JA-deficient mutant (aoc), we examined through kinetic transcriptome and physiological analysis the salt-triggered processes that are under JA control. Profound genotype-differential features emerged that could underlie observed phenotypes. ABA content and ABA-dependent water deprivation responses were impaired in aoc shoots. Moreover, aoc accumulated more Na + in roots, and less in leaf, with reduced ion translocation correlating with root derepression of the HAK4 Na + transporter. Distinct reactive oxygen species scavengers were also stronger in aoc leaf, along with reduced senescence and chlorophyll catabolism markers. Collectively, the data identify contrasted contributions of JA signaling to different sectors of the salt stress response in rice.

E3 ligase MaNIP1 degradation of NON-YELLOW COLORING1 at high temperature inhibits banana degreening.

Banana (Musa acuminata) fruit ripening under high temperatures (>24 °C) undergoes green ripening due to failure of chlorophyll degradation, which greatly reduces marketability. However, the mechanism underlying high temperature-repressed chlorophyll catabolism in banana fruit is not yet well understood. Here, using quantitative proteomic analysis, 375 differentially expressed proteins were identified in normal yellow and green ripening in banana. Among these, one of the key enzymes involved in chlorophyll degradation, NON-YELLOW COLORING 1 (MaNYC1), exhibited reduced protein levels when banana fruit ripened under high temperature. Transient overexpression of MaNYC1 in banana peels resulted in chlorophyll degradation under high temperature, which weakens the green ripening phenotype. Importantly, high temperature induced MaNYC1 protein degradation via the proteasome pathway. A banana RING E3 ligase, NYC1-interacting protein 1 (MaNIP1), was found to interact with and ubiquitinate MaNYC1, leading to its proteasomal degradation. Furthermore, transient overexpression of MaNIP1 attenuated MaNYC1-induced chlorophyll degradation in banana fruits, indicating that MaNIP1 negatively regulates chlorophyll catabolism by affecting MaNYC1 degradation. Taken together, the findings establish a post-translational regulatory module of MaNIP1-MaNYC1 that mediates high temperature-induced green ripening in bananas.

Proteasomal degradation of MaMYB60 mediated by the E3 ligase MaBAH1 causes high temperature-induced repression of chlorophyll catabolism and green ripening in banana.

Banana (Musa acuminata) fruits ripening at 30 °C or above fail to develop yellow peels; this phenomenon, called green ripening, greatly reduces their marketability. The regulatory mechanism underpinning high temperature-induced green ripening remains unknown. Here we decoded a transcriptional and post-translational regulatory module that causes green ripening in banana. Banana fruits ripening at 30 °C showed greatly reduced expression of 5 chlorophyll catabolic genes (CCGs), MaNYC1 (NONYELLOW COLORING 1), MaPPH (PHEOPHYTINASE), MaTIC55 (TRANSLOCON AT THE INNER ENVELOPE MEMBRANE OF CHLOROPLASTS 55), MaSGR1 (STAY-GREEN 1), and MaSGR2 (STAY-GREEN 2), compared to those ripening at 20 °C. We identified a MYB transcription factor, MaMYB60, that activated the expression of all 5 CCGs by directly binding to their promoters during banana ripening at 20 °C, while showing a weaker activation at 30 °C. At high temperatures, MaMYB60 was degraded. We discovered a RING-type E3 ligase MaBAH1 (benzoic acid hypersensitive 1) that ubiquitinated MaMYB60 during green ripening and targeted it for proteasomal degradation. MaBAH1 thus facilitated MaMYB60 degradation and attenuated MaMYB60-induced transactivation of CCGs and chlorophyll degradation. By contrast, MaMYB60 upregulation increased CCG expression, accelerated chlorophyll degradation, and mitigated green ripening. Collectively, our findings unravel a dynamic, temperature-responsive MaBAH1-MaMYB60-CCG module that regulates chlorophyll catabolism, and the molecular mechanism underpinning green ripening in banana. This study also advances our understanding of plant responses to high-temperature stress.

Cold pretreatment promotes chlorophyll degradation of green ripening banana peel by activating MaCBF1 to MaCBR and MaSGR1

Inhibition of peel de-greening in postharvest bananas under high temperature storage, resulting in green ripening, causes significant deterioration in fruit quality. Herein, we reported that cold treatment accelerated chlorophyll degradation of postharvest banana fruit at 30 °C, which was associated with the upregulated expression of MaCBR (Chlorophyll b reductase) and MaSGR1 (Stay-green 1). Moreover, cold treatment increased the expression of C-repeat binding factor MaCBF1. MaCBF1 bound directly to the promoters of MaCBR and MaSGR1 and activated their expressions. More importantly, transient expression of MaCBF1 in bananas enhanced chlorophyll degradation and weakened the repression of de-greening caused by high temperature. In summary, the cold treatment promotes chlorophyll catabolism by activating MaCBF1-induced transcriptional activation of MaCBR and MaSGR1, and attenuates high temperature-caused green ripening in bananas. These results study expand the understanding of the molecular events of high temperature-inhibited chlorophyll degradation and provide a feasible strategy to alleviate green ripening of banana fruit.

Physiological and transcriptomic analyses provide insight into thermotolerance in desert plant Zygophyllum xanthoxylum

BackgroundHeat stress has adverse effects on the growth and reproduction of plants. Zygophyllum xanthoxylum, a typical xerophyte, is a dominant species in the desert where summer temperatures are around 40 °C. However, the mechanism underlying the thermotolerance of Z. xanthoxylum remained unclear.ResultsHere, we characterized the acclimation of Z. xanthoxylum to heat using a combination of physiological measurements and transcriptional profiles under treatments at 40 °C and 45 °C, respectively. Strikingly, moderate high temperature (40 °C) led to an increase in photosynthetic capacity and superior plant performance, whereas severe high temperature (45 °C) was accompanied by reduced photosynthetic capacity and inhibited growth. Transcriptome profiling indicated that the differentially expressed genes (DEGs) were related to transcription factor activity, protein folding and photosynthesis under heat conditions. Furthermore, numerous genes encoding heat transcription shock factors (HSFs) and heat shock proteins (HSPs) were significantly up-regulated under heat treatments, which were correlated with thermotolerance of Z. xanthoxylum. Interestingly, the up-regulation of PSI and PSII genes and the down-regulation of chlorophyll catabolism genes likely contribute to improving plant performance of Z. xanthoxylum under moderate high temperature.ConclusionsWe identified key genes associated with of thermotolerance and growth in Z. xanthoxylum, which provide significant insights into the regulatory mechanisms of thermotolerance and growth regulation in Z. xanthoxylum under high temperature conditions.

Phytol recycling: essential, yet not limiting for tomato fruit tocopherol accumulation under normal growing conditions.

Tocopherols are potent membrane-bound antioxidant molecules that are paramount for plant physiology and also important for human health. In the past years, chlorophyll catabolism was identified as the primary source of phytyl diphosphate for tocopherol synthesis by the action of two enzymes, PHYTOL KINASE (VTE5) and PHYTHYL PHOSPHATE KINASE (VTE6) that are able to recycle the chlorophyll-derived phytol. While VTE5 and VTE6 were proven essential for tocopherol metabolism in tomato fruits, it remains unknown whether they are rate-limiting steps in this pathway. To address this question, transgenic tomato plants expressing AtVTE5 and AtVTE6 in a fruit-specific manner were generated. Although ripe transgenic fruits exhibited higher amounts of tocopherol, phytol recycling revealed a more intimate association with chlorophyll than with tocopherol content. Interestingly, protein-protein interactions assays showed that VTE5 and VTE6 are complexed, channeling free phytol and phytyl-P, thus mitigating their cytotoxic nature. Moreover, the analysis of tocopherol accumulation dynamics in roots, a chlorophyll-devoid organ, revealed VTE5-dependent tocopherol accumulation, hinting at the occurrence of shoot-to-root phytol trafficking. Collectively, these results demonstrate that phytol recycling is essential for tocopherol biosynthesis, even in chlorophyll-devoid organs, yet it is not the rate-limiting step for this pathway under normal growth conditions.

Exogenous melatonin ameliorates yellowing of postharvest pak choi (Brassica rapa subsp. chinensis) by modulating chlorophyll catabolism and antioxidant system during storage at 20 °C

The objective of this study was to investigate the regulatory mechanism of melatonin (MT) treatment on leaf yellowing of pak choi during storage at 20 °C. Results showed that 500 μmoL L−1 MT alleviated the yellowing process of pak choi as proved by the maintenance of high level of leaf colour, chlorophyll content and chlorophyll fluorescence parameters (Fo, Fm and Fv/Fm), and the market life of pak choi was extended by 2 d compared to the control. The weight loss and respiration rate were effectively alleviated by MT treatment. MT treatment restrained chlorophyll breakdown by down-regulating the activity of chlorophyll-degrading enzymes (chlorophyllase CLH, pheophytinase PPH and Mg-dechelatase MDS) and expression of their related genes (BcCLH, BcPPH1/2, BcSGR, BcHCAR, BcNYC1 and BcCAO). Meanwhile, MT suppressed the over-accumulation of reactive oxygen species (ROS) (superoxide anion O2·− and hydrogen peroxide H2O2), and lipid membrane oxidation and associated gene (BcLOX) expression during senescence, thus helping to keep green colour of pak choi. This relationship was also connected to the maintenance of higher level in antioxidant ability of antioxidase (superoxide dismutase SOD, ascorbate peroxidase APX, peroxidase POD and catalase CAT) and antioxidants (ascorbate-glutathione (AsA-GSH)), as well as high expression of their related genes (BcSOD, BcPOD, BcCAT, BcGPX and BcAPX) in pak choi treated with MT. In conclusion, these findings suggested that MT could delay the yellowing of pak choi, involving the regulation of chlorophyll metabolism, ROS metabolism, membrane lipid degradation, and antioxidant capacity. The results provide a possible target for delaying the yellowing of green vegetables.

Refrigeration, forchlorfenuron, and gibberellic acid treatments differentially regulate chlorophyll catabolic pathway to delay yellowing of broccoli

Postharvest broccoli has a high metabolic rate and senesces quickly. The most critical symptom of senescence is flower bud yellowing due to chlorophyll catabolism. Refrigeration and cytokinin treatment are effective means to retard broccoli yellowing; however, the mechanisms underlie are partially understood. Here, we examined the expression of NON-YELLOW COLORING1 (NYC1), CHLOROPHYLLASE1 (CLH1), CLH2, STAYGREEN1 (SGR1), SGR2, pheophytinase (PPH), pheophorbide a oxygenase (PAO), and other chlorophyll catabolic genes in broccoli and investigated the impact of refrigeration, forchlorfenuron (CPPU), and gibberellic acid (GA3) treatments on the expression of the genes. We found that SGR1 and PAO were most highly expressed, whereas expressions of CLH1 and CLH2 were low in fresh broccoli. Refrigeration and CPPU suppressed NYC1, SGR1, SGR2, and PAO while upregulating CLH1 or CLH2, whereas GA3 induced PPH and repressed CLH2. All 3 treatments retarded broccoli yellowing, and correlation analysis revealed that SGR1 and PAO were highly correlated with yellowing, while CLHs were inversely correlated with yellowing. Application of CPPU and GA3 stimulated mild but significant increases in ethylene production, suggesting cross-regulations between hormones during broccoli senescence. In conclusion, we elucidated the differential regulations of refrigeration, CPPU, and GA3 on chlorophyll catabolic genes and identified SGR1 and PAO as the most highly expressed and yellowing-related genes. These findings strengthen the understanding of broccoli senescence and may elicit new research and development of technologies to manipulate chlorophyll metabolism in postharvest crops.

MaNAC029 modulates ethylene biosynthesis and fruit quality and undergoes MaXB3-mediated proteasomal degradation during banana ripening

IntroductionsEthylene regulates ripening by activating various metabolic pathways that controlcolor, aroma, flavor, texture, and consequently, the quality of fruits. However, the modulation of ethylene biosynthesis and quality formation during banana fruit ripening remains unclear. ObjectivesThe present study aimed to identify the regulatory module that regulates ethylene and fruit quality-related metabolisms during banana fruit ripening. MethodsWe used RNA-seq to compare unripe and ripe banana fruits and identified a ripening-induced NAC transcription factor, MaNAC029. We further performed DNA affinity purification sequencing to identify the MaNAC029′s target genes involved in ethylene biosynthesis and fruit quality formation, and electrophoretic mobility shift assay, chromatin immunoprecipitation with real-time polymerase chain reaction and dual luciferase assays to explore the underlying regulatory mechanisms. Immunoprecipitation combined with mass spectrometry, yeast two-hybrid assay, and bimolecular fluorescence complementation assay were used to screen and verify the proteins interacting with MaNAC029. Finally, the function of MaNAC029 and its interacting protein associated with ethylene biosynthesis and quality formation was verified through transient overexpression experiments in banana fruits. ResultsThe study identified a nucleus-localized, ripening-induced NAC transcription factor MaNAC029. It transcriptionally activated genes associated with ethylene biosynthesis and a variety of cellular metabolisms related to fruit quality formation (cell wall degradation, starch degradation, aroma compound synthesis, and chlorophyll catabolism) by directly modulating their promoter activity during ripening. Overexpression of MaNAC029 in banana fruits activated ethylene biosynthesis and accelerated fruit ripening and quality formation. Notably, the E3 ligase MaXB3 interacted with and ubiquitinated MaNAC029 protein, facilitating MaNAC029 proteasomal degradation. Consistent with this finding, MaXB3 overexpression attenuated MaNAC029-enhanced ethylene biosynthesis and quality formation. ConclusionOur findings demonstrate that a MaXB3-MaNAC029 module regulates ethylene biosynthesis and a series of cellular metabolisms related to fruit quality formation during banana ripening. These results expand the understanding of the transcriptional and post-translational mechanisms of fruit ripening and quality formation.