Pheophorbide A Oxygenase Research Articles

SlTDC modulates photosynthesis of senescent leaves in tomato

Melatonin (MT) is a key regulator in plants’ response to leaf senescence induced by aging or various abiotic stresses. Here, we demonstrated that darkness and leaf aging enhance endogenous MT levels by upregulating key genes involved in MT synthesis. Additionally, exogenous MT application significantly mitigated leaf senescence induced by darkness and leaf aging in tomato plants, leading to higher chlorophyll content and maximum photochemical efficiency (Fv/Fm) compared to the control. Using Solanum lycopersicum L. tryptophan decarboxylase (SlTDC)-overexpressed and -knockout transgenic tomato seedlings, we found that SlTDC overexpression increased endogenous MT content and suppressed mRNA levels of chlorophyll degradation-related genes: pheophorbide a oxygenase (PAO), pheophytinase (PPH), and non-yellow coloring1 like (NOL). Furthermore, SlTDC overexpression alleviated photosystem II complex (PSII) photoinhibition, increased ribulose-1,5-bisphosphate carboxylase (Rubisco) and Rubisco activase (RCA) activities and mRNA levels, and maintained higher photosynthetic efficiency in leaves under darkness and in leaves aged over 35 d compared to wild-type plants. Conversely, SlTDC knockout accelerated darkness- or leaf aging-induced leaf senescence in tomatoes. Our findings suggest that MT application or SlTDC overexpression can effectively alleviate leaf senescence by regulating photosynthesis in tomato plants.

Greenhouse covering cultivation promotes chlorophyll accumulation of tea plant (Camellia sinensis) by activating relevant gene expression and enzyme activity

BackgroundThe tea plant (Camellia sinensis (L.) O. Kuntze) is one of the most economically important woody crops. Plastic greenhouse covering cultivation has been widely used in tea areas of northern China. Chlorophyll is not only the crucial pigment for green tea, but also plays an important role in the growth and development of tea plants. Currently, little is known about the effect of plastic greenhouse covering cultivation on chlorophyll in tea leaves.ResultsTo investigate the effect of plastic greenhouse covering cultivation on chlorophyll in tea leaves, color difference values, chlorophyll contents, gene expression, enzyme activities and photosynthetic parameters were analyzed in our study. Sensory evaluation showed the color of appearance, liquor and infused leaves of greenhouse tea was greener than field tea. Color difference analysis for tea liquor revealed that the value of ∆L, ∆b and b/a of greenhouse tea was significantly higher than field tea. Significant increase in chlorophyll content, intracellular CO2, stomatal conductance, transpiration rate, and net photosynthetic rate was observed in greenhouse tea leaves. The gene expression and activities of chlorophyll-metabolism-related enzymes in tea leaves were also activated by greenhouse covering.ConclusionThe higher contents of chlorophyll a, chlorophyll b and total chlorophyll in greenhouse tea samples were primarily due to higher gene expression and activities of chlorophyll-metabolism-related enzymes especially, chlorophyll a synthetase (chlG), pheophorbide a oxygenase (PAO) and chlorophyllide a oxygenase (CAO) in tea leaves covered by greenhouse. In general, our results revealed the molecular basis of chlorophyll metabolism in tea leaves caused by plastic greenhouse covering cultivation, which had great significance in production of greenhouse tea.

Comparative genomics analysis of pheophorbide a oxygenase (PAO) genes in eight pyrus genomes and their regulatory role in multiple stress responses in Chinese pear (Pyrus bretschneideri).

Pyrus (pear) is among the most nutritious fruits and contains fibers that have great health benefits to humans. It is mostly cultivated in temperate regions globally and is highly subjected to biotic and abiotic stresses which affect its yield. Pheophorbide a oxygenase (PAO) is an essential component of the chlorophyll degradation system and contributes to the senescence of leaves. It is responsible for opening the pheophorbide a porphyrin macrocycle and forming the main fluorescent chlorophyll catabolite However, this gene family and its members have not been explored in Pyrus genomes. Here we report a pangenome-wide investigation has been conducted on eight Pyrus genomes: Cuiguan, Shanxi Duli, Zhongai 1, Nijisseiki, Yunhong No.1, d'Anjou, Bartlett v2.0, and Dangshansuli v.1.1. The phylogenetic history, their gene structure, conservation patterns of motifs, their distribution on chromosomes, and gene duplication are studied in detail which shows the intraspecific structural conservation as well as evolutionary patterns of Pyrus PAOs. Cis-elements, protein-protein interactions (PPI), and the Gene Ontology (GO) enrichment analyses show their potential biological functions. Furthermore, their expression in various tissues, fruit hardening conditions, and drought stress conditions is also studied. Based on phylogenetics, the identified PAOs were divided into four groups. The expansion of this gene family in Pyrus is caused by both tandem and segmental duplication. Moreover, positive and negative selection pressure equally directed the gene's duplication process. The Pyrus PAO genes were enriched in hormones-related, light, development, and stress-related elements. RNA-seq data analysis showed that PAOs have varied levels of expression under diseased and abiotic stress conditions. The 3D structures of PAOs are also predicted to get more insights into functional conservation. Our research can be used further to get a deeper knowledge of the PAO gene family in Pyrus and to guide future research on improving the genetic composition of Pyrus to enhance stress tolerance.

Physiological and transcriptomic strategies related to photosynthesis of rice in response to vanadium stress

Vanadium (V) is recognized as an environmental contaminant that affects plant growth and development. However, the photosynthetic response of plants to V stress at molecular level remains unclear. In this study, we examined the photosynthetic responses of two rice varieties (Oryza sativa L.) with diverse V tolerance under various V levels (0, 10, 20, 30, and 40 mg L−1) using physiological, cytological, and transcriptomic approaches. Our findings indicated that V stress significantly reduced the photosynthetic rate and chlorophyll content in both genotypes, with the V-sensitive rice displaying a more pronounced reduction. Furthermore, we observed numerous plastoglobuli, deformed stroma, and ruptured thylakoid membranes in the chloroplasts of the V-sensitive rice. In transcriptome analysis, we found 34 differentially expressed genes of 21 enzymes potentially affect chlorophyll metabolism. Among them, most of the genes involved in chlorophyll biosynthesis and phototoxic intermediate degradation were down-regulated under V stress, while chlorophyll degradation-related genes exhibited up-regulation. In addition, the different expression levels of genes encoding uroporphyrinogen III synthase (UROS), protoporphyrinogen oxidase (PPO), chlorophyllase (CLH), pheophorbide a oxygenase (PAO), and red chlorophyll catabolite reductase (RCCR) between the two rice varieties may indicate a potential tolerance mechanism in rice plants in response to V stress. Overall, this study contributes to our understanding of the molecular mechanisms underlying plant tolerance to V toxicity, while also highlighting potential targets for improving plant tolerance in V-contaminated soils.

ABI5 promotes heat stress-induced chlorophyll degradation by modulating the stability of MYB44 in cucumber.

The yellowing of leaves caused by the decomposition of chlorophyll (Chl) is a characteristic event during senescence, which can be induced by various environmental stresses. However, the molecular mechanisms of high temperature-induced Chl degradation in horticultural plants remain poorly understood. Here, we found that heat stress induced Chl degradation and the expression of ABI5 and MYB44 in cucumber. Silencing of ABI5 compromised heat stress-induced Chl degradation, and the transcription of pheophytinase (PPH) and pheophorbide a oxygenase (PAO), two key genes in Chl catabolic pathway, but silencing of MYB44 exhibited the opposite results. Furthermore, ABI5 interacted with MYB44 in vitro and in vivo. ABI5 positively regulated heat stress-induced Chl degradation through two pathways. ABI5 directly bound to PPH and PAO promoters to promote their expression, leading to accelerating Chl degradation. On the other hand, the interaction between ABI5 and MYB44 reduced the binding of MYB44 to PPH and PAO promoters and led to the ubiquitination-depended protein degradation of MYB44, thereby alleviating the transcription inhibitory effect of MYB44 on PPH and PAO. Taken together, our findings propose a new regulatory network for ABI5 in regulating heat stress-induced Chl degradation.

Transcription factor LcNAC002 coregulates chlorophyll degradation and anthocyanin biosynthesis in litchi.

Chlorophyll degradation and anthocyanin biosynthesis, which often occur almost synchronously during fruit ripening, are crucial for vibrant coloration of fruits. However, the interlink point between their regulatory pathways remains largely unknown. Here, 2 litchi (Litchi chinensis Sonn.) cultivars with distinctively different coloration patterns during ripening, i.e. slow-reddening/stay-green "Feizixiao" (FZX) vs rapid-reddening/degreening "Nuomici" (NMC), were selected as the materials to study the key factors determining coloration. Litchi chinensis STAY-GREEN (LcSGR) was confirmed as the critical gene in pericarp chlorophyll loss and chloroplast breakdown during fruit ripening, as LcSGR directly interacted with pheophorbide a oxygenase (PAO), a key enzyme in chlorophyll degradation via the PAO pathway. Litchi chinensis no apical meristem (NAM), Arabidopsis transcription activation factor 1/2, and cup-shaped cotyledon 2 (LcNAC002) was identified as a positive regulator in the coloration of litchi pericarp. The expression of LcNAC002 was significantly higher in NMC than in FZX. Virus-induced gene silencing of LcNAC002 significantly decreased the expression of LcSGR as well as L. chinensis MYELOBLASTOSIS1 (LcMYB1), and inhibited chlorophyll loss and anthocyanin accumulation. A dual-luciferase reporter assay revealed that LcNAC002 significantly activates the expression of both LcSGR and LcMYB1. Furthermore, yeast-one-hybrid and electrophoretic mobility shift assay results showed that LcNAC002 directly binds to the promoters of LcSGR and LcMYB1. These findings suggest that LcNAC002 is an important ripening-related transcription factor that interlinks chlorophyll degradation and anthocyanin biosynthesis by coactivating the expression of both LcSGR and LcMYB1.

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.

DNA Methylation Inhibitor 5-Azacytidine Promotes Leaf Senescence in Pak Choi (Brassica rapa subsp. chinensis) by Regulating Senescence-Related Genes

Leaf senescence is strictly regulated by multiple internal factors and external environmental signals, with the epigenetic modification being an important element among them. However, the epigenetic mechanism of leaf senescence is largely unknown in horticultural crops, especially the leaf vegetable pak choi, which easily senesces, and becomes yellow post-harvest. In this study, we found that the expression of DNA methyltransferases (BcMET1, BcSUVH4, BcDRM2, BcRDR2, and BcCMT3) of pak choi decreased during storage. The preliminary results showed that its senescence process was accompanied by DNA methylation changes. Moreover, treatment with 500 μM 5-Azacytidine (5-Aza) (DNA methylation inhibitor) can promote the senescence of pak choi leaves by (1) increasing the degradation of chlorophyll (Chl) and its derivatives, (2) increasing the activities of Mg-dechelatase (MDCase), pheophytinase (PPH) and pheophorbide a oxygenase (PAO), and (3) inducing the expression of senescence-related genes (BcSAG12, BcNYC1, BcSGR1, BcSGR2, BcPPH1, BcPPH2, BcPAO, and BcRCCR), thereby accelerating the senescence of the pak choi leaves. Further studies showed that DNA demethylation occurred in the promoter regions of BcSGR2 and BcSAG12 during storage, with the bisulfite sequencing detection showing that their degrees of methylation decreased. Therefore, our findings help us understand how epigenetic modifications affect the storage tolerance of leafy vegetables, which is highly significant for cultivating anti-senescent vegetable varieties.

Upregulated expression of RESPIRATORY BURST OXIDASE HOMOLOG D underlies lesion-mimic phenotype in dark-treated Arabidopsis pheide a oxygenase mutant leaves.

Upregulated expression of RESPIRATORY BURST OXIDASE HOMOLOG D (RBOHD) encoding a plasma membrane NADPH oxidase is responsible for the lesion-mimic phenotype in detached Arabidopsis leaves with mutation of PHEIDE a OXYGENASE during extended darkness. Chlorophyll degradation is an indispensable process in leaf senescence, either age-dependent or dark-induced. Besides higher chlorophyll retention, a lesion-mimic phenotype (abbreviated as LMP afterwards) was exhibited in Arabidopsis leaves with mutation of PHEIDE a OXYGENASE (PaO) involved in chlorophyll degradation during dark incubation, but the associated mechanism remains elusive. We found that dark-treated pao leaves showed higher membrane damage and H2O2 accumulation, while scavenging H2O2 by its chemical scavenger diminished LMP. RBOHD which encodes NADPH oxidase was strikingly up-regulated in pao leaves during dark treatment. Chemical inhibition of NADPH oxidase or mutation of RBOHD in pao leaves suppressed LMP. Thus, our study suggests that up-regulated RBOHD transcription is responsible for the formation of LMP in dark-treated pao leaves and there may be a retrograde signaling pathway mediating upregulation of RBOHD which remains to be elucidated.

Low temperature delays degreening of apple fruit by inhibiting pheophorbide a oxygenase (PAO) pathway and chlorophyll oxidation during ripening.

The effects of low temperature (LT) on chlorophyll (Chl) degradation in peel of apple fruit during ripening were investigated. Apples collected at commercial maturity were stored at 4 ± 0.5°C. Our data indicated that LT treatment reduced respiration rate and ethylene production and slowed down softening of apple fruit during ripening. The LT treatment delayed increase in L*, a*, and b* values and decrease in Chl content compared with controls. The LT treatment reduced hydrogen peroxide (H2 O2 ) and malondialdehyde (MDA) contents and decelerated superoxide anion (O2 ·- ) production rate in chloroplast of peel compared with controls during ripening. The LT treatment differentially reduced activities of pheophytin pheophorbide hydrolase (PPH), Mg-dechelatase (MDcase), chlorophyll-degrading peroxidase (Chl-POX), and Chl oxidase, while enhanced SOD activity in chloroplast of peel during ripening. Expression levels of MdHCARa, MdNYC1, MdNYC3, MdNYE1, MdRCCR2, MdPPH1, MdPAO6, MdPAO8, and MdNOL2 in peel were differentially reduced by LT treatment during ripening. Our results indicated that LT treatment might delay Chl degradation through inhibiting PAO pathway and Chl oxidation during ripening of apple fruit. PRACTICAL APPLICATIONS: The LT is a common practice used to extend storage life of apple fruit. Degreening caused by Chl degradation is an integral part of fruit ripening, and elucidating its mechanism is an important subject for fruit quality maintenance. Our data indicated that LT delayed degreening of apple fruit by inhibiting PAO pathway and Chl oxidation during ripening. These results will provide useful information for clarifying molecular mechanisms of LT in regulation of degreening and also for quality maintenance of apple fruit.

VvERF17 mediates chlorophyll degradation by transcriptional activation of chlorophyll catabolic genes in grape berry skin

Chlorophylls in the skin contribute to grape (Vitis vinifera) berry color and quality. Degradation of chlorophyll occurs during berry development in grape, but less is known about the molecular mechanisms of this process. Here, we characterized an ethylene response factor, VvERF17, as a putative regulator of chlorophyll degradation in grape berry. VvERF17 expression was strongly correlates with development-induced and ETH-triggered chlorophyll degradation. Transient overexpression of VvERF17 in tobacco leaves, tomato fruits, and grape leaves led to color break and chlorophyll degradation, which were resulted from the upregulated expression of chlorophyll catabolic genes (CCGs), including Chlorophyll-b-reductase (NOL), pheophytinase (PPH), pheophorbide a oxygenase (PAO), and red Chlorophyll catabolite reductase (RCCR). Inversely, silencing of VvERF17 in grape leaves partially suppressed the expression of CCGs’ expression. Major CCGs’ expression was closely related to chlorophyll degradation and VvERF17 expression. It was further demonstrated that VvERF17 could activate the expression of major CCGs by directly binding to the ERF binding sites in their promoters. We conclude that VvERF17 mediates chlorophyll degradation by transcriptional activation of NOL, PPH, PAO, and RCCR. These findings elucidate the regulation mechanisms of chlorophyll degradation in grape and enrich our understanding of grape berry color formation.

Comprehensive insight into the chlorophyll degradation mechanism of postharvest broccoli heads under elevated O2 controlled atmosphere

Postharvest broccoli heads undergo yellowing quickly in unsuitable conditions, which diminishes their quality and commercial value. We investigated the pattern and molecular regulatory mechanism of chlorophyll (Chl) degradation in broccoli under elevated O2 controlled atmosphere. As results, the 40% O2 + 5% CO2 treatment accelerated the Chl degradation and the change in color of postharvest broccoli heads, while the 5% O2 + 5% CO2 treatment delayed the yellowing. The results indicated that Chl degradation pattern of postharvest broccoli heads concurrently involved the Pheide a oxygenase (PAO)/phyllobilin and oxidative degradation pathways, and the latter might be the dominant pathway of Chl degradation. The regulatory mechanism of elevated O2 on Chl degradation may be related to its ability to accelerate cell damage and death, destroy the light-harvesting complex II, and promote up-regulation of genes in the PAO/phyllobilin and oxidative degradation pathways. In contrast, low O2 treatment may down-regulate the expression of Chl degradation-related genes by increasing H2O2 content, thus delaying the yellowing of broccoli heads.

Transcriptome profiling of Stevia rebaudiana MS007 revealed genes involved in flower development.

Stevia rebaudiana is a medicinal plant recommended to diabetic or obese patients as an alternative sweetener owing to its low-calorie property. Previous studies have found that the stevioside level is highest at the time of flower bud formation and lowest at the time of preceding and following flower bud formation. Hence, this study aims to identify the genes involved in the flowering of local S. rebaudiana accession MS007 by investigating the transcriptomic data of two stages of growth, before flowering (BF) and after flowering (AF) that were deposited under accession number SRX6362785 and SRX6362784 at the NCBI SRA database. The transcriptomic study managed to annotate 108299 unigenes of S. rebaudiana with 8871 and 9832 genes that were differentially expressed in BF and AF samples, respectively. These genes involved in various metabolic pathways related to flower development, response to stimulus as well as photosynthesis. Pheophorbide A oxygenase ( PAO ), eukaryotic translation initiation factor 3 subunit E ( TIF3E1 ), and jasmonate ZIM domain-containing protein 1 ( JAZ1 ) were found to be involved in the flower development. The outcome of this study will help further research in the manipulation of the flowering process, especially in the breeding programme to develop photo-insensitive Stevia plant.

Octapeptide NOP-1 treatment delays yellowing in broccoli floret during low temperature storage

During postharvest life, floret yellowing confines broccoli's economic and nutritional worth. This study aimed to investigate the mechanisms activated by octapeptide NOP-1 (LKRYKRRL-NH2) treatment at 0, 250, 500, 750, or 1000 μM for retarding floret yellowing in broccoli during storage at 4 °C for 28 d. Our results revealed that the 750 μM NOP-1 treatment retarded chlorophyll degradation by suppressing pheophytinase (PPH) and pheophorbide a oxygenase (PaO) genes expression along with inhibiting Mg2+ dechelatase (MDC), and PPH enzymes activity. Besides, 750 μM NOP-1 treatment prevented jasmonic acid (JA) biosynthesis by suppressing phospholipase A (PLA), 13-lipoxygenase (13-LOX), allene oxide synthase (AOS), allene oxide cyclase (AOC), and OPDA reductase (OPR3) genes expression. Interestingly, 750 μM NOP-1 treatment maintained the membrane integrity in broccoli floret, evaluated by malondialdehyde (MDA) accumulation, which could be ascribed to the suppressing phosphatidylinositol 3-kinase (PI3K), phospholipase D (PLD), and 9-lipoxygenase (9-LOX) genes expression. Our results demonstrated that NOP-1, as an innovative, safe, and eco-friendly antisenescence octapeptide, significantly advances our technological proficiency to delay floret yellowing in broccoli during low temperature storage.

Delaying Broccoli Floret Yellowing by Phytosulfokine α Application During Cold Storage.

During postharvest life, broccoli suffers from floret yellowing confining its economic and nutritional value. The objective of the present study was to explore the mechanisms employed by phytosulfokine α (PSKα) at 150 nM for delaying floret yellowing in broccoli during storage at 4°C for 28 days. Our results showed that the higher endogenous accumulation of hydrogen sulfide (H2S) resulting from the higher gene expression and activities of l-cysteine desulfhydrase (LCD) and d-cysteine desulfhydrase (DCD) in broccoli floret treated with 150 nM PSKα may serve as an endogenous signaling molecule for delaying senescence. Moreover, the suppressed ethylene biosynthesis in broccoli floret treated with 150 nM PSKα might be ascribed to lower gene expression and activities of ACC synthase (ACS) and ACC oxidase (ACO). Furthermore, lower gene expression and activities of Mg2+ dechelatase (MDC), pheophytinase (PPH), and pheophorbide a oxygenase (PaO) might be the reasons for the higher accumulation of chlorophyll in broccoli floret treated with 150 nM PSKα. Based on our findings, exogenous PSKα application could be employed as signaling bioactive hormone for retarding floret yellowing of broccoli during storage at 4°C for 28 days.

Characterization of a novel allele encoding pheophorbide a oxygenase in rice

ABSTRACT We identified a rapid cell death 2 (rcd2) mutant from an indica cultivar Zhongjian100 mutant bank. The red-brown lesions appeared firstly on young seedling leaves, then gradually merged and the leaves completely withered at the late tillering stage. rcd2 displayed apparent cell death at/around the lesions, accumulation of superoxide anion (O2 −) and disturbed ROS scavenging system, impaired photosynthetic capacity with significantly reduced chlorophyll content. The lesion formation was controlled by a single recessive nuclear gene and induced by natural light as well as mechanical wounding. A single base mutation (A1726T) at the 6th exon of OsMH_03G0040800 resulted in I576F substitution in the encoding protein, pheophorbide a oxygenase (PAO). Functional complementation could rescue the mutant phenotype and PAO-knockout lines exhibited the similar phenotype to rcd2. The activity of PAO decreased significantly while the content of PAO substrate, pheophorbide a, increased apparently in rcd2. The expression of chlorophyll synthesis/degradation-related genes and the contents of metabolic intermediates were largely changed. Furthermore, the level of chlorophyllide a, the product of chlorophyllase, increased significantly, indicating chlorophyllase might play a role in chlorophyll degradation in rice. Our results suggested that the I576F substitution disrupted PAO function, leading to O2 − accumulation and chlorophyll degradation breakdown in rice.

Melatonin delays yellowing of broccoli during storage by regulating chlorophyll catabolism and maintaining chloroplast ultrastructure

• Exogenous melatonin markedly extended the shelf life of broccoli. • Melatonin delayed the decline of chlorophyll content and chloroplast breakdown. • Melatonin regulated activities and gene expressions of chlorophyll catabolic enzymes. • Melatonin regulated the expressions of BoSGR1 and BoSGR2 . The effect of melatonin treatment on color, chlorophyll degradation and chloroplast structure in broccoli during storage was evaluated. One hundred μmmol L −1 melatonin markedly extended the shelf life of broccoli. Compared with control florets, melatonin treatment delayed the decline of chlorophyll content, and maintained more intact chloroplasts. Meanwhile, melatonin also suppressed the activities of chlorophyll catabolic enzymes such as chlorophyllase (CLH), pheophytinase (PPH), pheophorbide a oxygenase (PAO) and red chlorophyll catabolite reductase (RCCR), and down-regulated the expressions of BoNYC1 , BoNOL , BoCLH , BoPPH , BoPAO , BoRCCR and BoSGR1 involved in chlorophyll catabolism. Taken together, our results indicated that melatonin could be a good candidate for delaying yellowing in broccoli during storage at 20 ℃.

Synergistic inhibitory effect of 1-methylcyclopropene (1-MCP) and chlorine dioxide (ClO2) treatment on chlorophyll degradation of green pepper fruit during storage

Abstract Degreening indicates the ripening and senescence process of green pepper fruit, which mainly results from chlorophyll degradation. To date, however, the effect of 1-Methylcyclopropene (1-MCP) alone or in combination with chlorine dioxide (ClO2) on the chlorophyll degradation pathway of green pepper at the molecular level remains scarce. In this study, green peppers were treated with 1 μL L−1 1-MCP, 30 μL L−1 ClO2 alone and 1 μL L−1 1-MCP plus 30 μL L−1 ClO2, respectively and stored at 20 °C for 12 d. The results showed that 1-MCP + ClO2 combination was superior in inhibiting color changes, decreasing the respiration rate, and exhibiting chlorophyll content as compared with 1-MCP or ClO2 alone. Further study on the expression of genes related to chlorophyll degradation pathway revealed that pheophytinase (PPH), pheophorbide a oxygenase (PAO) and red chlorophyll catabolite reductase (RCCR) were suppressed by all treatments. The efficiency of the combined treatment (1-MCP + ClO2) was better than that of 1-MCP or ClO2 alone. While the expression of chlorophyllase (CLH) was not affected by ClO2, but was significant suppressed by 1-MCP and 1-MCP + ClO2. Therefore, our results indicate the different regulatory roles of 1-MCP and ClO2 on the chlorophyll degradation pathway and provide an efficient method to preserve green pepper.

Transcriptome Analysis of Differentially Expressed Genes in Wild Jujube Seedlings under Salt Stress

Wild jujube (Ziziphus acidojujuba) and cultivated jujube (Ziziphus jujuba) belong to the family Rhamnaceae. Jujubes have marked drought- and salt-tolerant properties. After salt stress, wild jujube seedling growth was inhibited and photosynthetic efficiency was reduced. A bioinformatics approach was used to analyze the transcriptomics data from wild jujube seedlings grown under salt stress, and the genes differentially expressed under the salt stress were identified to provide a theoretical basis for the development and use of wild jujube plantations in salinized soil. The transcriptome sequencing from leaves of wild jujube seedlings was carried out using second-generation sequencing technology. The effects of salt stress on the differential expression of photosynthesis-related genes in wild jujube seedlings were analyzed. Transcriptome sequencing revealed a total of 5269 differentially expressed genes (DEGs), of which 2729 were up-regulated and 2540 were down-regulated. DEGs were mainly enriched with respect to photosynthesis, photosynthetic antenna proteins, glyoxylic acid and dicarboxylic acid metabolism, linolenic acid metabolism, cysteine and methionine metabolism, and porphyrin and chlorophyll metabolism. Among them, the photosynthesis pathway-related DEGs were most highly enriched. Further analysis of porphyrin and chlorophyll synthesis and photosynthesis-related pathways revealed that they were significantly enriched by 97 photosynthesis-related DEGs. The DEGs in the photosynthesis and photosynthetic antenna protein pathways were down-regulated, whereas the DEGs glutamyl-tRNA reductase (HEMA), ferrochelatase (HEMH), and pheophorbide a oxygenase (PAO) in the porphyrin and chlorophyll synthesis pathways were up-regulated, with the remainder being down-regulated. The nuclear gene encoding Rubisco, the key enzyme in the photosynthetic carbon fixation pathway, was also down-regulated. The results showed that the photosynthetic rate of wild jujube seedlings decreased following exposure to salinity stress, an effect that was related to the increased synthesis of 5-aminolevulinic acid and heme, and the up-regulation of expression of a gene encoding a chlorophyll-degrading enzyme, and was related to the down-regulation of gene expression in photosynthesis-related pathways such as light energy capture and carbon fixation. Selection of nine DEGs related to photosynthesis and chlorophyll biosynthesis by quantitative real-time-PCR confirmed that expression changes of these nine DEGs were consistent with the transcriptome sequencing results.

Pheophorbide a May Regulate Jasmonate Signaling during Dark-Induced Senescence.

Chlorophyll degradation is one of the most visible signs of leaf senescence. During senescence, chlorophyll is degraded in the multistep pheophorbide a oxygenase (PAO)/phyllobilin pathway. This pathway is tightly regulated at the transcriptional level, allowing coordinated and efficient remobilization of nitrogen toward sink organs. Using a combination of transcriptome and metabolite analyses during dark-induced senescence of Arabidopsis (Arabidopsis thaliana) mutants deficient in key steps of the PAO/phyllobilin pathway, we show an unanticipated role for one of the pathway intermediates, i.e. pheophorbide a Both jasmonic acid-related gene expression and jasmonic acid precursors specifically accumulated in pao1, a mutant deficient in PAO. We propose that pheophorbide a, the last intact porphyrin intermediate of chlorophyll degradation and a unique pathway "bottleneck," has been recruited as a signaling molecule of chloroplast metabolic status. Our work challenges the assumption that chlorophyll breakdown is merely a result of senescence, and proposes that the flux of pheophorbide a through the pathway acts in a feed-forward loop that remodels the nuclear transcriptome and controls the pace of chlorophyll degradation in senescing leaves.