Chlorophyll Degradation Pathway Research Articles

Effects of microplastics and combined pollution of polystyrene and di-n-octyl phthalate on photosynthesis of cucumber (Cucumis sativus L.)

Photosynthesis provides carbon sources and energy for crop growth and development, and the widespread presence of microplastics and plastic plasticisers in agricultural soils affects crop photosynthesis, but the mechanism of the effect is not clear. This study aims to investigate the effects of different microplastics and plasticizers on cucumber photosynthesis. Using polyvinyl chloride (PVC), polyethylene (PE), polystyrene (PS), and di-n-octyl phthalate (DOP) as representative microplastics and plasticizers, we assessed their impact on cucumber photosynthesis. Our results reveal significant alterations in key parameters: intercellular CO2 concentration (Ci) and transpiration rate (Tr) increased across all treatments, whereas stomatal limit value (Ls) and water use efficiency (WUE) decreased. Notably, PS + DOP treatment led to a significant reduction in the maximum efficiency of photosystem II (Fv/Fm) and ATP accumulation. Furthermore, PE and PS + DOP treatments decreased lycopene and ɛ-carotene synthesis rates, as well as abscisic acid (ABA) accumulation. All treatments inhibited the conversion of β-carotene into strigolactone (SL) and decreased chlorophyll synthesis rates, with PS + DOP exhibiting the most severe impact. Regarding chlorophyll degradation pathways, PVC and PE treatments reduced chlorophyll decomposition rates, whereas DOP with PS promoted degradation. PE and PS treatments also impaired light energy capture, electron transport, and the structural stability of photosystems I and II, as well as photosynthetic capacity and NADPH and ATP synthesis rates. Our findings underscore the differential impacts of microplastics and plasticizers on cucumber photosynthesis, with PS + DOP having the most detrimental effect. These results shed light on the complex interactions between microplastics and plant physiology, highlighting the urgent need for mitigation strategies in agricultural practices to safeguard crop productivity and environmental sustainability.

Transcription factor CrWRKY42 coregulates chlorophyll degradation and carotenoid biosynthesis in citrus.

Chlorophyll degradation and carotenoid biosynthesis, which occur almost simultaneously during fruit ripening, are essential for the coloration and nutritional value of fruits. However, the synergistic regulation of these 2 processes at the transcriptional level remains largely unknown. In this study, we identified a WRKY transcription factor, CrWRKY42, from the transcriptome data of the yellowish bud mutant "Jinlegan" ([Citrus unshiu × C. sinensis] × C. reticulata) tangor and its wild-type "Shiranui" tangor, which was involved in the transcriptional regulation of both chlorophyll degradation and carotenoid biosynthesis pathways. CrWRKY42 directly bound to the promoter of β-carotene hydroxylase 1 (CrBCH1) and activated its expression. The overexpression and interference of CrWRKY42 in citrus calli demonstrated that CrWRKY42 promoted carotenoid accumulation by inducing the expression of multiple carotenoid biosynthetic genes. Further assays confirmed that CrWRKY42 also directly bound to and activated the promoters of the genes involved in carotenoid biosynthesis, including phytoene desaturase (CrPDS) and lycopene β-cyclase 2 (CrLCYB2). In addition, CrWRKY42 could bind to the promoters of NONYELLOW COLORING (CrNYC) and STAY-GREEN (CrSGR) and activate their expression, thus promoting chlorophyll degradation. The overexpression and silencing of CrWRKY42 in citrus fruits indicated that CrWRKY42 positively regulated chlorophyll degradation and carotenoid biosynthesis by synergistically activating the expression of genes involved in both pathways. Our data revealed that CrWRKY42 acts as a positive regulator of chlorophyll degradation and carotenoid biosynthesis to alter the conversion of citrus fruit color. Our findings provide insight into the complex transcriptional regulation of chlorophyll and carotenoid metabolism during fruit ripening.

Functional Validation and Promoter DNA Methylation Analysis of the OfPAO Gene of Osmanthus fragrans ‘Yinbi Shuanghui’

Osmanthus fragrans ‘Yinbi Shuanghui’ is a colored leaf variety of O. fragrans. To study the mechanism of leaf color formation in O. fragrans ‘Yinbi Shuanghui’, we selected green and colored leaves with two different parts, namely yellow and green, as our research materials. We analyzed the expression changes related to leaf color in genes by performing qRT-PCR in the different leaf parts, finding that OfPAO was significantly up-regulated in the yellow part of colored leaves, and we initially determined that OfPAO was the key gene involved in the formation of colored leaves. Then, we constructed an OfPAO overexpression vector, before transforming it into tobacco through an Agrobacterium-mediated transformation to obtain transgenic plants. We found that the transgenic tobacco leaf color of OfPAO was lighter than that of the null carrier, the chlorophyll content in leaves decreased, and the expression of genes involved in the chlorophyll degradation pathway in OfPAO transgenic tobacco was up-regulated, suggesting that OfPAO regulates chlorophyll degradation, leading to changes in leaf color. According to the results of transcriptome sequencing and the genome data of O. fragrans ‘Rixianggui’, we cloned CDS and the promoter sequence of OfPAO, and the promoter regions 901-1307 of the OfPAO were sequenced through bisulfite genomic sequencing PCR (BSP), finding that the methylation level of CHH in the yellow part of colored leaves was lowest in colored and green leaves at 145 bp. The methylation of CHH in the promoter of OfPAO in O. fragrans ‘Yinbi Shuanghui’ was negatively correlated with the gene expression level, suggesting that the methylation of the promoter of OfPAO may regulate the expression of OfPAO, affecting chlorophyll degradation in the leaves.

The potential mechanism of UpCrtR-b regulates leaf color change in Ulmus pumila by multi-omics and functional analysis

Ulmus pumila ‘Zhonghua Jinye’ is an important landscape tree species because of its golden leaves. Leaf coloration is the main factor that determines the ornamental and economic value of U. pumila. Gene expression and metabolite accumulation patterns were studied by transcriptome and metabolome to explore the physiological and molecular mechanisms of leaf color changes in U. pumila. The results showed that the leaf color change of U. pumila was regulated by the metabolism of chlorophyll, flavonoids, and carotenoids. The content of total chlorophyll and chlorophyll a decreased gradually with seasonal changes, which was mainly caused by the obstruction of chlorophyll synthesis and the activation of the chlorophyll degradation pathway. Among them, the expression level of chlorophyll synthesis-related genes (GluTR, UROD, PPO, and POR) were down-regulated, while certain genes (CHLG, CAO, HCAR, PPH, and PAO) in the chlorophyll degradation pathway were significantly up-regulated. In addition, flavonoids gradually accumulated with seasonal changes. Among them, twenty-six key genes (PAL, 4CL, CHS, F3H, FLS, 3GT, DFR, and ANS) in flavonoid biosynthesis were involved in regulation of flavonol and anthocyanin biosynthesis. Furthermore, carotenoids (lutein, zeaxanthin, and β-carotene) were also mainly accumulated in July and August. Finally, the candidate gene, UpCrtR-b, in carotenoid biosynthesis was identified in the present study and was found to be expressed in plastids by functional verification. In tobacco, overexpression of UpCrtR-b could increase carotenoid accumulation and make tobacco leaves yellowish. This study revealed the molecular mechanism of leaf color regulation in U. pumila, and provided a theoretical basis for better utilization of this species as a landscape tree, which also provides the possibility for further enriching the variation mechanism and cultivating colored leaf plants.

STAY-GREEN Accelerates Chlorophyll Degradation in Magnolia sinostellata under the Condition of Light Deficiency.

Species of the Magnoliaceae family are valued for their ornamental qualities and are widely used in landscaping worldwide. However, many of these species are endangered in their natural environments, often due to being overshadowed by overstory canopies. The molecular mechanisms of Magnolia's sensitivity to shade have remained hitherto obscure. Our study sheds light on this conundrum by identifying critical genes involved in governing the plant's response to a light deficiency (LD) environment. In response to LD stress, Magnolia sinostellata leaves were endowed with a drastic dwindling in chlorophyll content, which was concomitant to the downregulation of the chlorophyll biosynthesis pathway and upregulation in the chlorophyll degradation pathway. The STAY-GREEN (MsSGR) gene was one of the most up-regulated genes, which was specifically localized in chloroplasts, and its overexpression in Arabidopsis and tobacco accelerated chlorophyll degradation. Sequence analysis of the MsSGR promoter revealed that it contains multiple phytohormone-responsive and light-responsive cis-acting elements and was activated by LD stress. A yeast two-hybrid analysis resulted in the identification of 24 proteins that putatively interact with MsSGR, among which eight were chloroplast-localized proteins that were significantly responsive to LD. Our findings demonstrate that light deficiency increases the expression of MsSGR, which in turn regulates chlorophyll degradation and interacts with multiple proteins to form a molecular cascade. Overall, our work has uncovered the mechanism by which MsSGR mediates chlorophyll degradation under LD stress conditions, providing insight into the molecular interactions network of MsSGR and contributing to a theoretical framework for understanding the endangerment of wild Magnoliaceae species.

Targeted Metabolome and Transcriptome Analyses Reveal the Pigmentation Mechanism of Hippophae (Sea Buckthorn) Fruit

The genus Hippophae (sea buckthorn) is widely cultivated and consumed in Asia and Europe. The fruit color is an important appearance and commercial trait for sea buckthorn, which is closely related to the biosynthesis and accumulation of various nutrients and pigments. The fruit colors of sea buckthorn are varied, which appear as yellow, orange, red, and brown. However, the nutrients and pigments forming different the fruit colors of sea buckthorn remain unclear. To investigate the mechanism of pigmentation of sea buckthorn fruit, integrative analyses of the transcriptome and targeted metabolome, including the carotenoids, flavonoids, and chlorophylls, were performed in five sea buckthorn varieties with different fruit colors. A total of 209 flavonoids and 41 carotenoids were identified in five sea buckthorn fruits of different colors. The types and contents of flavonoids and carotenoids in the five sea buckthorn fruits were significantly different. Interestingly, we only found a high content of chlorophyll (772.7 mg/kg) in the sea buckthorn fruit with a brown color. The quantities and relative proportions of the flavonoids, carotenoids, and chlorophyll led to the different colors of the sea buckthorn fruits. Using a weighted gene co-expression network analysis (WGCNA), the key genes related to the carotenoids and chlorophyll metabolism were identified. The high content of chlorophylls in the brown fruit was closely related to the downregulated expression of key genes in the chlorophyll degradation pathway, including SGR, SGRL, PPH, NYC1, and HCAR. Our results provide new insights into the roles of flavonoids, carotenoids, and chlorophylls in the formation of fruit color in sea buckthorn.

Crystal structure and reaction mechanism of a bacterial Mg-dechelatase homolog from the Chloroflexi Anaerolineae.

Chlorophyll degradation plays a myriad of physiological roles in photosynthetic organisms, including acclimation to light environment and nutrient remobilization during senescence. Mg extraction from chlorophyll a is the first and committed step of the chlorophyll degradation pathway. This reaction is catalyzed by the Mg-dechelatase enzyme encoded by Stay-Green (SGR). The reaction mechanism of SGR protein remains elusive since metal ion extraction from organic molecules is not a common enzymatic reaction. Additionally, experimentally derived structural information about SGR or its homologs has not yet been reported. In this study, the crystal structure of the SGR homolog from Anaerolineae bacterium was determined using the molecular replacement method at 1.85 Å resolution. Our previous study showed that three residues-H32, D34, and D62 are essential for the catalytic activity of the enzyme. Biochemical analysis involving mutants of D34 residue further strengthened its importance in the functioning of the dechelatase. Docking simulation also revealed the interaction between the D34 side chain and central Mg ion of chlorophyll a. Structural analysis showed the arrangement of D34/H32/D62 in the form of a catalytic triad that is generally found in hydrolases. The probable reaction mechanism suggests that deprotonated D34 side chain coordinates and destabilizes Mg, resulting in Mg extraction. Besides, H32 possibly acts as a general base catalyst and D62 facilitates H32 to be a better proton acceptor. Taken together, the reaction mechanism of SGR partially mirrors the one observed in hydrolases.

VvERF95 regulates chlorophyll degradation by transcriptional activation of VvPAO1 causing grape rachis degreening after harvesting

• Ethylene plays important role during rachis degreening, expression of VvERF95 can be induced by ethylene. • VvERF95 upregulate VvPAO1 expression by binding to DRE cis -element in its promoter. • Transgenic plants of VvERF95 have lower chlorophyll content and transcript level of VvPAO1 and the other CCGs were increased. Rachis degreening is one of the main problems during postharvest storage of grape, its regulatory mechanism remains obscure. Here, we found that production of ethylene was increased and chlorophyll content was decreased during rachis degreening of Shine Muscat grape, while the reverse were observed after 1-MCP (1-methylcyclopropene) treatment. The ethylene transcription factor VvERF95 was isolated, and its transcriptional changes were closely correlated with chlorophyll content during rachis browning. The expression of VvERF95 was induced by ethylene and inhibited by 1-MCP. Dual-luciferase, yeast one-hybrid and EMSA assays, as well as motif mutation experiments, indicated that VvERF95 can bind to the promoter of pheophorbide a oxygenase ( VvPAO1 ) and upregulate its transcript levels. Overexpression of VvERF95 in grape lead to chlorophyll degradation in grape leaves, and increases in the transcript levels of VvPAO1 and most genes in the chlorophyll degradation pathway. Collectively, our findings decipher the mechanism of ethylene-enhanced chlorophyll degradation in grape, and will be useful for manipulating chlorophyll accumulation in grape and other plants.

DNA Methylation and RNA-Sequencing Analysis to Identify Genes Related to Spontaneous Leaf Spots in a Wheat Variety ‘Zhongkenuomai No.1’

Greenish leaf variation has been reported widely as a trait of great interest in wheat for improving photosynthesis. Zhongkenuomai No.1 (ZKNM1), a mutant with recoverable leaf spots, was regarded as a suitable material for studying chlorophyll synthesis-related mechanisms. In this study, transcriptome and DNA methylation analyses were conducted in ZKNM1 leaves to determine the transcriptional regulatory mechanism of leaf spot development. Ultimately, 890 differentially expressed genes (DEGs) were discovered, with chlorophyll biosynthesis pathway genes downregulated and chlorophyll degradation pathway genes upregulated, possibly acting as a double block to chlorophyll accumulation. Among them, HEMA1s (Glutamyl-tRNA reductase family proteins) and PORAs (protochlorophyllide oxidoreductase A) were the most important controlled genes. Furthermore, a genome-wide methylation analysis indicates that a hypermethylated region is present 1690 bp upstream of the transcriptional start sites in spot tissues (SPs), and 131 DNA methylation-mediated DEGs were identified, one of which encoded a putative resistance gene (TraesCS1A02G009500) and was a hub gene in interaction network modules. In the sample groups with leaf spots (SPs), this gene may be involved in the photosynthetic processes. The findings indicated that dynamic variations in DNA methylation play key roles in gene regulation to govern leaf spot development.

Physiological and iTRAQ-based proteomic analyses for yellowing of postharvest broccoli heads under elevated O2 controlled atmosphere

Controlled atmosphere storage has been proved to be an effective measure to regulate chlorophyll degradation. The obvious inhibitory effect of CO2 on chlorophyll degradation was widely studied, but information available on the promotion of chlorophyll degradation by elevated O2 was limited. The present work aimed to investigate the regulation of different O2 concentrations on yellowing of broccoli heads during storage by physiology and proteomics. As expected, 40% O2 + 5% CO2 treatment promoted the chlorophyll degradation and carotenoid synthesis, and thus to accelerate the yellowing of broccoli heads. In addition, elevated O2 decreased the ascorbic acid, glucosinolate, and flavonoid contents and increased the MDA content. A total of 189 proteins related to the yellowing of broccoli heads were identified as differentially expressed proteins (fold change ≥1.20 or ≤0.83). These proteins were mainly associated with pigment metabolism, thylakoid structure, photosynthetic system, chloroplast ribosome, antioxidant substance metabolism, and antioxidant enzyme metabolism. The proteomics results showed 40% O2 + 5% CO2 treatment disrupted antioxidant metabolism and aggravated oxidative stress compared with 5% O2 + 5% CO2 and 20% O2 + 5% CO2 treatments, thus leading to the destruction of photosystems I and II, thylakoid membrane, and chloroplast ribosome in broccoli heads. In addition, 40% O2 + 5% CO2 treatment accelerated the yellowing of postharvest broccoli heads by down-regulating chlorophyll biosynthetic pathway and the expression of apolipoproteins (light-harvesting complex I, II, and oxygen-evolving enhancer protein) and ribulose-1,5-bisphosphate carboxylase (Rubisco), and up-regulating chlorophyll degradation and carotenoid biosynthetic pathways. This study might improve our understanding of yellowing acceleration mechanisms of broccoli heads by elevated O2, thereby promoting the development of new broccoli heads preservation technology.

Comparative transcriptome analysis to identify fruit coloration-related genes of late-ripening litchi mutants and their wild type

Litchi (Litchi chinensis Sonn.) is an important subtropical fruit crop with high economic and nutritional values. Fruit coloration is a sign of litchi fruit ripening and an important external quality traits. Two continuous generations of mutants, named MS1 and MS2, originally derived from cultivar ‘Heli’, exhibited the distinctive characteristic of late maturation of 20 d, with observable delays in coloration. The present study aimed to understand the mechanism underlying maturation difference between ‘Heli’ and its two mutants. An RNA-seq analysis revealed 6,145 differentially expressed genes, mostly identified at the color-breaking stage. The maximum expression levels of some genes involved in anthocyanin biosynthesis and chlorophyll degradation were delayed in the pericarp of the mutants compared with in the original cultivar. Generally, they peaked at earlier stages (S2/S3) in ‘Heli’, compared with later stages (S4/S5) in mutants. Moreover, some hormonal signal receptors, especially those involved in abscisic and ethylene signaling pathways, were also differentially expressed between the original cultivar and the mutant. Transcription factors, including MYB, bHLH, bZIP, and WRKY, correlated with anthocyanin biosynthesis, chlorophyll degradation and abscisic acid signal pathways were identified. The late pigmentation in mutants was related to the fruit ripening program, a complex and comprehensive process. Additionally, we identified novel candidate genes that are involved in the regulation of litchi fruit pigmentation of and gained significant insights into the process of litchi fruit ripening.

Degradation of the photosystem II core complex is independent of chlorophyll degradation mediated by Stay-Green Mg2+ dechelatase in Arabidopsis

During leaf senescence, the degradation of photosystems and photosynthetic pigments proceeds in a coordinated manner, which would minimize the potential photodamage to cells. Both photosystem I and II are composed of core complexes and peripheral antenna complexes, with the former binding chlorophyll a and the latter binding chlorophyll a and b. Although the degradation of peripheral antenna complexes is initiated by chlorophyll degradation, it remains unclear whether the degradation of core complexes and chlorophyll is coordinated. In this study, we examined the degradation of peripheral antenna and core complexes in the Arabidopsis sgr1/sgr2/sgrl triple mutant, lacking all the isoforms of chlorophyll a:Mg2+ dechelatase. In this mutant, the degradation of peripheral antenna complexes and photosystem I core complexes was substantially retarded, but the core complexes of photosystem II were rapidly degraded during leaf senescence. On the contrary, the photosynthetic activity declined at a similar rate as in the wild type plants. These results suggest that the degradation of photosystem II core complexes is regulated independently of the major chlorophyll degradation pathway mediated by the dechelatase. The study should contribute to the understanding of the complex molecular mechanisms underlying the degradation of photosystems, which is an essential step during leaf senescence.

Insights into the structure and function of the rate-limiting enzyme of chlorophyll degradation through analysis of a bacterial Mg-dechelatase homolog

The Mg-dechelatase enzyme encoded by the Stay-Green (SGR) gene catalyzes Mg2+ dechelation from chlorophyll a. This reaction is the first committed step of chlorophyll degradation pathway in plants and is thus indispensable for the process of leaf senescence. There is no structural information available for this or its related enzymes. This study aims to provide insights into the structure and reaction mechanism of the enzyme through biochemical and computational analysis of an SGR homolog from the Chloroflexi Anaerolineae (AbSGR-h). Recombinant AbSGR-h with its intact sequence and those with mutations were overexpressed in Escherichia coli and their Mg-dechelatase activity were compared. Two aspartates – D34 and D62 were found to be essential for catalysis, while R26, Y28, T29 and D114 were responsible for structural maintenance. Gel filtration analysis of the recombinant AbSGR-h indicates that it forms a homo-oligomer. The three-dimensional structure of AbSGR-h was predicted by a deep learning-based method, which was evaluated by protein structure quality evaluation programs while structural stability of wild-type and mutant forms were investigated through molecular dynamics simulations. Furthermore, in concordance with the results of enzyme assay, molecular docking concluded the significance of D34 in ligand interaction. By combining biochemical analysis and computational prediction, this study unveils the detailed structural characteristics of the enzyme, including the probable pocket of interaction and the residues of structural and functional importance. It also serves as a basis for further studies on Mg-dechelatase such as elucidation of its reaction mechanism or inhibitor screening.

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.

Expression of BoNOL and BoHCAR genes during postharvest senescence of broccoli heads.

Chlorophyll is the most abundant pigment on Earth, essential for the capture of light energy during photosynthesis. During senescence, chlorophyll degradation is highly regulated in order to diminish toxicity of the free chlorophyll molecule due to its photoactivity. The first step in the chlorophyll degradation pathway is the conversion of chlorophyll b to chlorophyll a by means of two consecutive reactions catalyzed by enzymes coded by NYC1 (NON-YELLOW COLORING 1), NOL (NYC1-LIKE) and HCAR. In this work, we studied the expression of NOL and HCAR genes during postharvest senescence of broccoli. We found that the expression of BoNOL increase during the first days of storage and then decrease. In the case of BoHCAR, its expression is maintained during the first days and then it also diminishes. Additionally, the effect of different postharvest treatments on the expression of these genes was also analyzed. It was observed that the expression of BoNOL is lower in the treatments performed with 1-methylcyclopropene (1-MCP), 6-benzylaminopurine (6-BAP) and modified atmospheres, while BoHCAR expression showed an increase in these same treatments, and a decrease in the treatment with ethylene. There were no variations in the expression of both genes in heat treatment, UV-C treatment and visible light treatment. These results suggest that both BoHCAR and BoNOL show a lower regulation of their expression than other genes involved in chlorophyll degradation during senescence. © 2020 Society of Chemical Industry.

High-throughput sequencing reveals the molecular mechanisms determining the stay-green characteristic in soybeans

Senescence is an internally systematized degeneration process leading to death in plants. Leaf yellowing, one of the most prominent features of plant aging may lead to reduced crop yields. The molecular mechanism of responses to senescence in soybean leaves is not completely clear. In our research, two soybean varieties were selected with different stay-green traits: stay-green variety (BN106) and non-stay-green variety (KF14). RNA samples extracted from the leaves of two varieties were sequenced and compared using high-throughput sequencing. Six key enzyme genes in chlorophyll degradation pathways were studied to analyze the changes in their expression at seedling, flowering and maturation stage. Meanwhile, the construction of the genetic transformation process had been constructed to identify the function of putative gene by RNA-interference. A total of 4329 DEGs were involved in 52 functional groups and 254 KEGG pathways. Twelve genes encoding senescence-associated and inducible chloroplast stay-green protein showed significant differential expression. MDCase and PAO have a significant expression in BN106 that may be the key factors affecting the maintenance of green characteristics. In addition, the function of GmSGRs has been identified by genetic transformation. The loss of GmSGRs may cause soybean seeds to change from yellow to green. In summary, our results revealed fundamental information about the molecular mechanism of aging in soybeans with different stay-green characteristics. The work of genetic transformation lays a foundation for putative gene function studies that could contribute to postpone aging in soybeans.

Autophagy-Related 2 Regulates Chlorophyll Degradation under Abiotic Stress Conditions in Arabidopsis.

Chloroplasts are extraordinary organelles for photosynthesis and nutrient storage in plants. During leaf senescence or under stress conditions, damaged chloroplasts are degraded and provide nutrients for developing organs. Autophagy is a high-throughput degradation pathway for intracellular material turnover in eukaryotes. Along with chloroplast degradation, chlorophyll, an important component of the photosynthetic machine, is also degraded. However, the chlorophyll degradation pathways under high light intensity and high temperature stress are not well known. Here, we identified and characterized a novel Arabidopsis mutant, sl2 (seedling lethal 2), showing defective chloroplast development and accelerated chlorophyll degradation. Map-based cloning combined with high-throughput sequencing analysis revealed that a 118.6 kb deletion region was associated with the phenotype of the mutant. Complementary experiments confirmed that the loss of function of ATG2 was responsible for accelerating chlorophyll degradation in sl2 mutants. Furthermore, we analyzed chlorophyll degradation under abiotic stress conditions and found that both chloroplast vesiculation and autophagy take part in chlorophyll degradation under high light intensity and high temperature stress. These results enhanced our understanding of chlorophyll degradation under high light intensity and high temperature stress.

Comprehensive study of the genes involved in chlorophyll synthesis and degradation pathways in some monocot and dicot plant species

Chlorophyll (Chl) biosynthesis is one of the most important cellular processes essential for plant photosynthesis. Chl degradation pathway is also important catabolic process occurs during leaf senescence, fruit ripening and under biotic or abiotic stress conditions. Here we have systematically investigated the molecular evolution, gene structure, compositional analysis along with ENc plot, correspondence analysis and codon usage bias of the proteins and encoded genes involved in Chl metabolism from monocots and dicots. The gene and species specific phylogenetic trees using amino acid sequences showed clear clustering formation of the selected species based on monocots and dicots but not supported by 18S rRNA. Nucleotide composition of the encoding genes showed that average GC%, GC1%, GC2% and GC3% were higher in monocots. RSCU analysis depicts that genes from monocots for both pathways and genes for synthesis pathway from dicots only biased to G/C-ending synonymous codons but in degradation pathway most optimal codons (except UUG) in dicots biased to A/U-ending synonymous codons. We found strong evidence of episodic diversifying selection at several amino acid sites in all genes investigated. Conserved domain and gene structures were observed for the genes with varying lengths of introns and exons, involved in Chl metabolism along with some intronless genes within synthesis pathway. ENc and correspondence analyses suggested the mutational or selection constraint on the genes to shape the codon usage. These comprehensive studies may be helpful in further research in molecular phylogenetics and genomics and to better understand the evolutionary dynamics of Chl metabolic pathway. Communicated by Ramaswamy H. Sarma

Proline-stimulated signaling primarily targets the chlorophyll degradation pathway and photosynthesis associated processes to cope with short-term water deficit in maize.

Increased photosynthetic efficiencies in genotypes with greater proline level and in crops treated with proline under water deficit have been reported in recent years, but the biochemical and molecular mechanisms of this process are still not known. We examined photosystem II (PSII) activity, photosynthetic enzymes, ribulose 1,5-bisphosphate carboxylase/oxygenase (rubisco), phosphoenolpyruvate carboxylase (PEPc), rubisco activase (RCA), and chlorophyll metabolic enzymes, magnesium chelatase (Mg-CHLI), and chlorophyllase (Chlase), which would be the primary targets of exogenous proline to provide photosynthetic protection to plants under PEG-induced short-term water deficit. Two maize genotypes W23/M14 with greater proline content and Şafak with low proline content were hydroponically grown for 21-23days, and then the seedlings were subjected to water deficit (- 0.75MPa) induced by PEG6000 for 0, 4, and 8h. Before the seedlings were exposed to the water deficit, proline (1mM) was applied to the rooting medium of the Şafak genotype for 2days. The time course effects of the applications showed that exogenous proline significantly enhanced PSII efficiency, PEPc activity, rubisco activity, and the relative expression levels of PEPc, rubisco large subunit, rubisco small subunit, and RCA genes at 0, 4, and 8h. The W23/M14 genotype had higher rubisco quantity than the Şafak genotype at all time periods. Proline pre-treatment under the stress-free and PEG conditions reduced the activity of Chlase and the gene expressions of Chlase, while it enhanced Mg-CHLI gene expression at 0, 4, and 8h. Taken together, the results indicated that the primary target of proline-stimulated signaling in maize seedlings exposed to short-term severe water deficit may be to induce PSII efficiency, activities of carbon dioxide fixation enzymes and chlorophyll metabolism and mitigate chlorophyll degradation.

Transcriptomic investigation of the basis of Corona and petal colour in Chinese narcissus

ABSTRACT Chinese narcissus is a traditional flower with gorgeous corona and petal colour. The carotenoid biosynthesis pathway is primarily responsible for colour formation in narcissus flower. However, the role of carotenoid biosynthesis enzymes and intermediates in colour development, and the molecular basis of differences between orange-yellow corona and milky-white petals are unclear. Here, we performed RNA-Seq using Illumina HiSeq platform and de novo transcriptome assembly to predict the functions of the identified significantly differentially expressed genes (DEGs). We investigated genes expression in narcissus corona and petal tissues on the first and seventh day of flowering. 14 colour -related genes were further analysed by qRT-PCR. The significantly DEGs encoded various kinds of enzymes and transcription factors (TFs) associated with carotenoid and flavonoid biosynthesis pathways, respectively. These DEGs mainly included phytoene synthase ( PSY ) gene, lycopene epsilon cyclase ( LCYE ) gene, β-carotene hydroxylase ( BCH ) gene, β-carotene isomerase gene and AP2/ ERF, B3, MYB, NAC and WRKY TFs. Additionally, an in-depth analysis of chlorophyll biosynthesis and degradation pathways was performed. These results enhance our understanding of the mechanism of colour formation in narcissus flower and provide a basis for further investigation of the functions of proteins encoded by the annotated unigenes and cDNA sequences of narcissus.