Chlorophyll Synthesis Pathway Research Articles

Research on lncRNA related to drought resistance of Shanlan upland rice

BackgroundDrought has become the major abiotic stress that causes losses in rice yields and consequently is one of the main environmental factors threatening food security. Long non-coding RNA (lncRNA) is known to play an important role in plant response to drought stress, while the mechanisms of competing endogenous RNA (ceRNA) in drought resistance in upland rice have been rarely reported.ResultsIn our study, a total of 191 lncRNAs, 2115 mRNAs and 32 miRNAs (microRNAs) were found by strand-specific sequencing and small RNA sequencing to be differentially expressed in drought-stressed rice. Functional analysis of results indicate that they play important roles in hormone signal transduction, chlorophyll synthesis, protein synthesis and other pathways. Construction of a ceRNA network revealed that MSTRG.28732.3 may interact with miR171 in the chlorophyll biosynthesis pathway and affect the ability of plants to withstand drought stress by regulating Os02g0662700, Os02g0663100 and Os06g0105350. The accuracy of the regulatory network was verified by qRT-PCR.ConclusionOur results provide a theoretical basis for future studies on the potential function of lncRNA in plant drought resistance, and they provide new genetic resources for drought-resistant rice breeding.

5-Aminolevulinic acid and hydrogen sulphide alleviate chilling stress in pepper (Capsicum annuum L.) seedlings by enhancing chlorophyll synthesis pathway

5- Aminolevulinic acid (ALA) as a precursor in chlorophyll (Chl) synthesis and hydrogen sulphide (H2S) as a gas signalling molecules can alleviate various abiotic stresses by enhancing photosynthesis. However, little is known about their mechanisms ameliorating photosynthesis under chilling stress, or interactions of ALA and H2S in Chl synthesis. In this study, we explored the effects of exogenous ALA and H2S on chilling stress-induced photosynthesis damage in pepper (Capsicum annuum L.) seedlings. Chilling inhibited the photosynthetic capacity of pepper seedlings, ALA or H2S treatment alone could alleviate this inhibition, and ALA + H2S treatment was even more effective for improving photosynthetic capacity. Additionally, levels of Chl synthesis pathway substances including endogenous ALA, protoporphyrin IX (Proto IX), Mg-protoporphyrin (Mg-Proto IX), protochlorophyllide (Pchl) and Chl (Chl a and Chl b) were significantly decreased, and chilling down-regulated upstream genes HEMA1, HEMB, FAR1, FHY3, CHLH, HEME1, HEMF and PORA. ALA + H2S treatment significantly increased levels of Chl and upstream substances, and up-regulated expression of HEMA1, HEMB and FAR1. In conclusion, exogenous ALA and H2S enhanced chlorophyll synthesis pathway, and thus improved the photosynthesis of pepper seedlings under chilling stress.

Comparative analysis of the metabolome and transcriptome between green and albino zones of variegated leaves from Hydrangea macrophylla ‘Maculata’ infected by hydrangea ringspot virus

In nature, many different factors cause plants to present variegated leaves. The purpose of this study was to reveal the changes in the green and albino leaves of Hydrangea macrophylla ‘Maculata’. It was found that in the albino zone, the leaves became thinner, the chloroplast structure disappeared, and a large number of leucoplasts replaced chloroplasts. In addition, the albino zone of the leaves contained almost no chlorophyll and showed no function related to transforming and utilizing light energy, and more intense oxidative stress was observed in the albino zone of the leaves than in the green zone. RNA-seq analysis showed that the chlorophyll synthesis pathway of the albino zone of leaves was blocked. Upregulated expression of the hydrangea ringspot virus (HdRSV) coat protein (CP) gene was detected in albino tissue by RT-qPCR. Finally, combined UPLC-MS/MS and RNA-seq analyses revealed metabolic changes involving multiple pathways in albino leaf tissue, centered on the TCA cycle. We hypothesize that HdRSV may alter energy metabolism in the albino zone of leaves, including increased lipid metabolism, reduced sugar metabolism, and increased synthesis of amino acids and the viral capsid protein from ribosomes.

Comparative transcriptome and proteome profiling of chlorophyll metabolism pathway in four types of Magnolia officinalis

Magnolia officinalis is a traditional Chinese medicine,with many years of cultivating process, M. officinalis leaves show more differentiation types due to the exchange of seeds from different provenances. "Da Ao"(DA), "Xiao Ao"(XA), "Chuan Hou"(CH),and "Liu Ye"(LY)are the main types of M. officinalis in Sichuan province of China,and there were obvious differences in growth rate,chemical composition,leaf shape and leaf colour. This study selected different types of M. officinalis leaves(DA,XA,LY and CH)from Sichuan to determine their chlorophyll content. Transcriptomic level sequencing of different types of M. officinalis leaf tissues was by high-throughput sequencing analysis and proteomics used an integrated approach involving TMT labelling and LC-MS/MS to quantify the dynamic changes of the whole proteome of M. officinalis. The results showed that CH had the lowest chlorophyll content while DA had the highest chlorophyll content. Furthermore,transcriptome and proteomics results showed that chlorophyll synthesis pathway in DA glutamine-tRNA reductase,urinary porphyrins decarboxylase(UROD),oxygen-dependent protoporphyrin(ODCO),the original-Ⅲ oxidase protoporphyrin oxidase(PPO),magnesium chelating enzyme subunit ChlD,protoporphyrin magnesium Ⅸ monomethyl ester [oxidative] cyclase(MPPMC)were significantly higher than CH,XA and LY,consistent in the results of determination of chlorophyll content(chlorophyll content was highest of 37.56 mg·g~(-1) FW). Some rate-limiting enzymes related to the chlorophyll synthesis,such as ODCO,PPO and MPPMC were tested by Parallel Reaction Monitoring(PRM),and the results showed that the rate-limiting enzyme content in DA was higher than that in other three types. Therefore,based on the differences in leaf color of four types of M. officinalis,the research conducted a preliminary study on the chlorophyll metabolism pathway in leaves of different types of M. officinalis,and explored relevant genes and proteins causing leaf color differences from the molecular level,so as to lay a foundation for studying the differences in growth and development of different types of M. officinalis.

Alleviation of cadmium toxicity by mercapto-triazole priming in wheat

ABSTRACT Cadmium happens to interfere with chlorophyll synthesis, calvin cycle and phosphate pathway and the resulting changes in biochemical attributes induce disorders in physiology, biochemistry and genetics of the germinating plants. Its hazardous effects disturb the phenolic contents, sugars, soluble proteins and activities of antioxidant enzymes. We employed mercapto-triazoles as wheat seed priming agents and evaluated their potential to alleviate the negative impact of cadmium stress (5 µM) on biochemical attributes in germinating seedlings. For priming, 10, 20, 30 and 40 mg L−1 solution of each triazolic compound was used and the germination was carried out under normal and Cd stress conditions. Biochemical attributes including sugars, protein contents, total phenolic, total oxidant status, hydrolytic enzymes and antioxidant enzymes were studied under both conditions and compared with control. Almost all triazolic-priming significantly alleviated the deleterious impacts of cadmium and improved protein contents, SOD, POD, and esterase activities with a significant reduction in MDA contents. The decrease in MDA along with the increase in above-said biochemical attributes in wheat seedlings suggests the mitigating effects of tested triazoles against cadmium stress.

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.

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

Genetic dissection of photochemical efficiency under water-deficit stress in rice

Chlorophyll fluorescence (Chl-F) measurements together with non-invasive estimations of chlorophyll content, can be used to investigate functionally rich or poor photosystem II (PSII), relating to alterations in photosynthetic performances under different abiotic stresses. The aim was to identify genetic loci that control rice capacity to cope with different soil moisture conditions such as non-stress (control), water deficit and recovery during the reproductive stage. A genome-wide association study was performed for effective quantum yield of photosystem II (QY) and chlorophyll index across all three treatments. Accessions showed significant variability in traits within each treatment. A total of 43 genetic loci associated with QY and chlorophyll index were identified. Of the total genetic loci identified, 14 were for control, 13 for water-deficit stress and 16 for recovery responses. Interestingly, the majority of the identified genetic loci were co-localized either with chlorophyll synthesis or degradation pathways, components of PSII, transcription factors, protein kinases, transporters, kinases, and antioxidants genes. Favorable alleles and donor accessions found in our study would complement efforts aimed at stacking of traits. Moreover, our results provide promising genetic information for future validation and a potential resource for improving photochemical efficiency and subsequently enhancing carbon gain in rice under water-limited conditions.

Effects of light intensity on metabolism of light-harvesting pigment and photosynthetic system in Camellia sinensis L. cultivar ‘Huangjinya’

‘Huangjinya’ (HJY) is a light-sensitive chlorotic tea cultivar (Camellia sinensis L.) that grows chlorotic shoots under sun-light conditions but its chlorotic shoots turn green under weak light conditions. However, the mechanisms responsible for light intensity-induced changes in leaf color remain unclear. In this study, we compared HJY plants with chlorotic leaves exposed to sun-light (Y) and HJY plants with green leaves exposed to both sun and shade (Y + S) on the basis of metabolite profiles, expression of proteins and genes in the pigment metabolic pathway and photosynthetic system. We found that the main hindered sites in chlorophyll synthesis pathway of Y were from COPP III to PP IX and the down-regulation of POR and CAO further inhibited the synthesis of chlorophyll a and b. In addition, the gene and protein expression of ACD1, the key site of chlorophyll degradation, was significantly up-regulated in Y, indicating that sunlight also enhanced the degradation of chlorophyll in HJY. The contents of antenna protein, PSII and PSI-related protein in Y were significantly decreased, and photosynthetic electron transport was blocked, resulting in a significant decrease in photosynthetic efficiency of HJY.

Physiological characterization and transcriptome analysis of a chlorosis mutant in pak choi

Leaf color mutants are not only ideal resources for studying the physiological mechanisms of plant photosynthesis, but they are also selection markers for hybrid production. In this study, the chlorosis mutant ‘564Y’ and its wild-type counterpart ‘564’ were used to explore physiological characteristics and gene expression in pak choi. Compared with those of wild type, the dry weight and fresh weight of ‘564Y’ were significantly reduced, but the hypocotyl length of ‘564Y’ was longer. Pigment analysis showed that the chlorophyll a and carotenoid contents of ‘564Y’ were lower than those of wild type. However, there was no significant difference in chlorophyll b content between these two varieties. The photosynthetic capacity of ‘564Y’ was lower than that of ‘564’, and the photosynthetic electron transfer ability and light energy conversion efficiency were weaker in the former. Transmission electron microscopy showed that the chloroplast structure of ‘564Y’ was not compact, the thylakoid structure was irregular, and the number of matrix, grana, and stacking layers was decreased. Transcriptome analysis revealed 2958 differentially expressed genes (DEGs), and 78 gene ontology terms and 35 Kyoto Encyclopedia of Genes and Genomes pathways were significantly enriched. Among the DEGs, nine genes were associated with the chlorophyll synthesis pathway (Bra031690, Bra012595, Bra005677, Bra022628, Bra026410, Bra032155, Bra039206, Bra029875, and Bra012511) and one gene was associated with photosynthesis (Bra038011). Among these genes, 3 were identified as related to auxin metabolism too (Bra032155, Bra039206, and Bra029875). Their differential expression in the ‘564Y’ mutant and wild-type plant was confirmed by qRT-PCR. These results lay the foundation for future genetic and functional genomic studies in pak choi.

Field-grown soybean transcriptome shows diurnal patterns in photosynthesis-related processes.

Many plant physiological processes have diurnal patterns regulated by diurnal environmental changes and circadian rhythms, but the transcriptional underpinnings of many of these cycles have not been studied in major crop species under field conditions. Here, we monitored the transcriptome of field‐grown soybean (Glycine max) during daylight hours in the middle of the growing season with RNA‐seq. The analysis revealed 21% of soybean genes were differentially expressed over the course of the day. Expression of some circadian‐related genes in field‐grown soybean differed from previously reported expression patterns measured in controlled environments. Many genes in functional groups contributing to and/or depending on photosynthesis showed differential expression, with patterns particularly evident in the chlorophyll synthesis pathway. Gene regulatory network inference also revealed seven diurnally sensitive gene nodes involved with circadian rhythm, transcription regulation, cellular processes, and water transport. This study provides a diurnal overview of the transcriptome for an economically important field‐grown crop and a basis for identifying pathways that could eventually be tailored to optimize diurnal regulation of carbon gain.

5-Aminolevulinic Acid (ALA) Alleviated Salinity Stress in Cucumber Seedlings by Enhancing Chlorophyll Synthesis Pathway.

5-Aminolevulinic acid (ALA) is a common precursor of tetrapyrroles as well as a crucial growth regulator in higher plants. ALA has been proven to be effective in improving photosynthesis and alleviating the adverse effects of various abiotic stresses in higher plants. However, little is known about the mechanism of ALA in ameliorating the photosynthesis of plant under abiotic stress. In this paper, we studied the effects of exogenous ALA on salinity-induced damages of photosynthesis in cucumber (Cucumis sativus L.) seedlings. We found that the morphology (plant height, leave area), light utilization capacity of PS II [qL, Y(II)] and gas exchange capacity (Pn, gs, Ci, and Tr) were significantly retarded under NaCl stress, but these parameters were all recovered by the foliar application of 25 mg L-1 ALA. Besides, salinity caused heme accumulation and up-regulation of gene expression of ferrochelatase (HEMH) with suppression of other genes involved in chlorophyll synthesis pathway. Exogenously application of ALA under salinity down-regulated the heme content and HEMH expression, but increased the gene expression levels of glutamyl-tRNA reductase (HEMA1), Mg-chelatase (CHLH), and protochlorophyllide oxidoreductase (POR). Moreover, the contents of intermediates involved in chlorophyll branch were increased by ALA, including protoporphyrin IX (Proto IX), Mg-protoporphyrin IX (Mg-Proto IX, protochlorophyllide (Pchlide), and chlorophyll (Chl a and Chl b) under salt stress. Ultrastructural observation of mesophyll cell showed that the damages of photosynthetic apparatus under salinity were fixed by ALA. Collectively, the chlorophyll biosynthesis pathway was enhanced by exogenous ALA to improve the tolerance of cucumber under salinity.

Impaired Magnesium Protoporphyrin IX Methyltransferase (ChlM) Impedes Chlorophyll Synthesis and Plant Growth in Rice.

Magnesium protoporphyrin IX methyltransferase (ChlM) catalyzes the formation of magnesium protoporphyrin IX monomethylester (MgPME) from magnesium protoporphyrin IX (MgP) in the chlorophyll synthesis pathway. However, no ChlM gene has yet been identified and studied in monocotyledonous plants. In this study, a spontaneous mutant, yellow-green leaf 18 (ygl18), was isolated from rice (Oryza sativa). This mutant showed yellow-green leaves, decreased chlorophyll level, and climate-dependent growth differences. Map-based cloning of this mutant identified the YGL18 gene LOC_Os06g04150. YGL18 is expressed in green tissues, especially in leaf organs, where it functions in chloroplasts. YGL18 showed an amino-acid sequence similarity to that of ChlM from different photosynthetic organisms. In vitro enzymatic assays demonstrated that YGL18 performed ChlM enzymatic activity, but ygl18 had nearly lost all ChlM activity. Correspondingly, the substrate MgP was largely accumulated while the product MgPME was reduced in ygl18 leaves. YGL18 is required for light-dependent and photoperiod-regulated chlorophyll synthesis. The retarded growth of ygl18 mutant plants was caused by the high light intensity. Moreover, the higher light intensity and longer exposure in high light intensity even made the ygl18 plants be more susceptible to death. Based on these results, it is suggested that YGL18 plays essential roles in light-related chlorophyll synthesis and light intensity–involved plant growth.

The xantha Marker Trait Is Associated with Altered Tetrapyrrole Biosynthesis and Deregulated Transcription of PhANGs in Rice.

The xantha marker trait, which is controlled by a down-regulating epi-mutation of OsGUN4, has been applied to the production of hybrid rice. However, the molecular basis for the ability of xantha mutants to attain high photosynthetic capacity even with decreased chlorophyll contents has not been characterized. In the present study, we observed that the total chlorophyll content of the xantha mutant was only 27.2% of that of the wild-type (WT) plants. However, the xantha mutant still accumulated 59.9% of the WT δ-aminolevulinic acid content, 72.8% of the WT Mg-protoporphyrin IX content, and 63.0% of the WT protochlorophyllide a content. Additionally, the protoporphyrin IX and heme contents in the mutant increased to 155.0 and 160.0%, respectively, of the WT levels. A search for homologs resulted in the identification of 124 rice genes involved in tetrapyrrole biosynthesis and photosynthesis. With the exception of OsGUN4, OsHO-1, and OsHO-2, the expression levels of the genes involved in tetrapyrrole biosynthesis were significantly higher in the xantha mutant than in the WT plants, as were all 72 photosynthesis-associated nuclear genes. In contrast, there were no differences between the xantha mutant and WT plants regarding the expression of all 22 photosynthesis-associated chloroplast genes. Furthermore, the abundance of 1O2 and the expression levels of 1O2-related genes were lower in the xantha mutant than in the WT plants, indicating 1O2-mediated retrograde signaling was repressed in the mutant plants. These results suggested that the abundance of protoporphyrin IX used for chlorophyll synthesis decreased in the mutant, which ultimately decreased the amount of chlorophyll in the xantha mutant. Additionally, the up-regulated expression of photosynthesis-associated nuclear genes enabled the mutant to attain a high photosynthetic capacity. Our findings confirm that OsGUN4 plays an important role in tetrapyrrole biosynthesis and photosynthesis in rice. GUN4, chlorophyll synthesis pathways, and photosynthetic activities are highly conserved in plants and hence, novel traits (e.g., xantha marker trait) may be generated in other cereal crops by modifying the GUN4 gene.

Exogenous spermidine is enhancing tomato tolerance to salinity-alkalinity stress by regulating chloroplast antioxidant system and chlorophyll metabolism.

BackgroundSalinity–alkalinity stress is known to adversely affect a variety of processes in plants, thus inhibiting growth and decreasing crop yield. Polyamines protect plants against a variety of environmental stresses. However, whether exogenous spermidine increases the tolerance of tomato seedlings via effects on chloroplast antioxidant enzymes and chlorophyll metabolism is unknown. In this study, we examined the effect of exogenous spermidine on chlorophyll synthesis and degradation pathway intermediates and related enzyme activities, as well as chloroplast ultrastructure, gene expression, and antioxidants in salinity–alkalinity–stressed tomato seedlings.ResultsSalinity–alkalinity stress disrupted chlorophyll metabolism and hindered uroorphyrinogen III conversion to protoporphyrin IX. These effects were more pronounced in seedlings of cultivar Zhongza No. 9 than cultivar Jinpengchaoguan. Under salinity–alkalinity stress, exogenous spermidine alleviated decreases in the contents of total chlorophyll and chlorophyll a and b in seedlings of both cultivars following 4 days of stress. With extended stress, exogenous spermidine reduced the accumulation of δ–aminolevulinic acid, porphobilinogen, and uroorphyrinogen III and increased the levels of protoporphyrin IX, Mg–protoporphyrin IX, and protochlorophyllide, suggesting that spermidine promotes the conversion of uroorphyrinogen III to protoporphyrin IX. The effect occurred earlier in cultivar Jinpengchaoguan than in cultivar Zhongza No. 9. Exogenous spermidine also alleviated the stress–induced increases in malondialdehyde content, superoxide radical generation rate, chlorophyllase activity, and expression of the chlorophyllase gene and the stress–induced decreases in the activities of antioxidant enzymes, antioxidants, and expression of the porphobilinogen deaminase gene. In addition, exogenous spermidine stabilized the chloroplast ultrastructure in stressed tomato seedlings.ConclusionsThe tomato cultivars examined exhibited different capacities for responding to salinity–alkalinity stress. Exogenous spermidine triggers effective protection against damage induced by salinity–alkalinity stress in tomato seedlings, probably by maintaining chloroplast structural integrity and alleviating salinity–alkalinity–induced oxidative damage, most likely through regulation of chlorophyll metabolism and the enzymatic and non–enzymatic antioxidant systems in chloroplast. Exogenous spermidine also exerts positive effects at the transcription level, such as down–regulation of the expression of the chlorophyllase gene and up–regulation of the expression of the porphobilinogen deaminase gene.

Mg-chelatase I subunit 1 and Mg-protoporphyrin IX methyltransferase affect the stomatal aperture in Arabidopsis thaliana.

To elucidate the molecular mechanisms of stomatal opening and closure, we performed a genetic screen using infrared thermography to isolate stomatal aperture mutants. We identified a mutant designated low temperature with open-stomata 1 (lost1), which exhibited reduced leaf temperature, wider stomatal aperture, and a pale green phenotype. Map-based analysis of the LOST1 locus revealed that the lost1 mutant resulted from a missense mutation in the Mg-chelatase I subunit 1 (CHLI1) gene, which encodes a subunit of the Mg-chelatase complex involved in chlorophyll synthesis. Transformation of the wild-type CHLI1 gene into lost1 complemented all lost1 phenotypes. Stomata in lost1 exhibited a partial ABA-insensitive phenotype similar to that of rtl1, a Mg-chelatase H subunit missense mutant. The Mg-protoporphyrin IX methyltransferase (CHLM) gene encodes a subsequent enzyme in the chlorophyll synthesis pathway. We examined stomatal movement in a CHLM knockdown mutant, chlm, and found that it also exhibited an ABA-insensitive phenotype. However, lost1 and chlm seedlings all showed normal expression of ABA-induced genes, such as RAB18 and RD29B, in response to ABA. These results suggest that the chlorophyll synthesis enzymes, Mg-chelatase complex and CHLM, specifically affect ABA signaling in the control of stomatal aperture and have no effect on ABA-induced gene expression.Electronic supplementary materialThe online version of this article (doi:10.1007/s10265-014-0636-0) contains supplementary material, which is available to authorized users.

Identification and Gene Mapping of Leaf Pale Yellow-Revertible Mutant pyr1 in Rice

It is important for the further understanding of the relationship between chlorophyll synthesis and degradation pathways and plant photosynthesis to identify and clone leaf color mutant gene. A leaf pale yellow-revertible mutant temporarily designated as pyr1 was obtainted from the progeny of rice (Oryza sativa L.) restorer line Jinhui 10 which was induced by ethyl methane sulfonate (EMS). In the seedling stage, the whole leaf of mutants presented pale and some mutants died. The pyr1 displayed different colors in different growth periods. At the booting stage upper-leaf and leaf margin exhibited yellow. Compared with the wild type, the chlorophyl contents of pyr1 mutant decreased from seedling stage to filling stage. Transmission electronic microscopy observation showed that the structure of cells had no obvious differences between mutant and wild type, but the chloroplast developed abnormally with degradation of the inside and matrix slices. Genetic analysis revealed that the trait was controlled by one recessive gene. With 326 recessive individuals from the F 2 segregation population, the PYR1 gene was finally mapped between RM11722 and Ind1 on the long arm of chromosome 1, with an approximate physical distance of 92 kb. These results provide a basis of PYR1 gene cloning by map-based strategy.

Transcriptomes of the Parasitic Plant Family Orobanchaceae Reveal Surprising Conservation of Chlorophyll Synthesis

Parasitism in flowering plants has evolved at least 11 times [1]. Only one family, Orobanchaceae, comprises all major nutritional types of parasites: facultative, hemiparasitic (partially photosynthetic), and holoparasitic (nonphotosynthetic) [2]. Additionally, the family includes Lindenbergia, a nonparasitic genus sister to all parasitic Orobanchaceae [3-6]. Parasitic Orobanchaceae include species with severe economic impacts: Striga (witchweed), for example, affects over 50 million hectares of crops in sub-Saharan Africa, causing more than $3 billion in damage annually [7]. Although gene losses and increased substitution rates have been characterized for parasitic plant plastid genomes [5, 8-11], the nuclear genome and transcriptome remain largely unexplored. The Parasitic Plant Genome Project (PPGP; http://ppgp.huck.psu.edu/) [2] is leveraging the natural variation in Orobanchaceae to explore the evolution and genomic consequences of parasitism in plants through a massive transcriptome and gene discovery project involving Triphysaria versicolor (facultative hemiparasite), Striga hermonthica (obligate hemiparasite), and Phelipanche aegyptiaca (Orobanche [12]; holoparasite). Here we present the first set of large-scale genomic resources for parasitic plant comparative biology. Transcriptomes of above-ground tissues reveal that, in addition to the predictable loss of photosynthesis-related gene expression in P.aegyptiaca, the nonphotosynthetic parasite retains an intact, expressed, and selectively constrained chlorophyll synthesis pathway.

Using Algal Transcriptome Sequences to Identify Transferred Genes in the Sea Slug, Elysia chlorotica

The first molecular evidence of horizontal gene transfer between multicellular eukaryotes was our discovery of the presence of three Vaucheria litorea nuclear-encoded genes [fucoxanthin chlorophyll a/c-binding protein (fcp) and light-harvesting complex 1 and 2 (Lhcv1 and 2)] in the genomic DNA of the sea slug, Elysia chlorotica, which are used to support the chloroplast endosymbiosis in the slug. These genes are translated and transcribed in the host cell, and vertically transmitted to subsequent generations of the host species. In order to provide a database of native V. litorea sequences to facilitate the search for additional transferred genes between these two species, we have partially sequenced and annotated the transcriptome of V. litorea, using 454 Life Science’s next generation pyrosequencing technology. Preliminary analysis of the sequence data has led to the discovery of six additional algal nuclear genes in E. chlorotica cDNA and genomic DNA, which encode enzymes in the chlorophyll synthesis pathway as well as additional light-harvesting and metabolic enzymes. Furthermore, we confirm the recent discovery of the Calvin-Benson cycle gene, prk.

EIN3/EIL1 cooperate with PIF1 to prevent photo-oxidation and to promote greening of Arabidopsis seedlings

The ability to switch from skotomorphogenesis to photomorphogenesis is essential for seedling development and plant survival. Recent studies revealed that COP1 and phytochrome-interacting factors (PIFs) are key regulators of this transition by repressing the photomorphogenic responses and/or maintaining the skotomorphogenic state of etiolated seedlings. Here we report that the plant hormone ethylene plays a crucial role in the transition from skotomorphogenesis to photomorphogenesis by facilitating greening of etiolated seedlings upon light irradiation. Activation of EIN3/EIL1 is both necessary and sufficient for ethylene-induced enhancement of seedling greening, as well as repression of the accumulation of protochlorophyllide, a phototoxic intermediate of chlorophyll synthesis. EIN3/EIL1 were found to induce gene expression of two key enzymes in the chlorophyll synthesis pathway, protochlorophyllide oxidoreductase A and B (PORA/B). ChIP and EMSA assays demonstrated that EIN3 directly binds to the specific elements present in the PORA and PORB promoters. Genetic studies revealed that EIN3/EIL1 function in cooperation with PIF1 in preventing photo-oxidative damage and promoting cotyledon greening. Moreover, activation of EIN3 reverses the blockage of greening triggered by cop1 mutation or far-red light irradiation. Consistently, EIN3 acts downstream of COP1 and its protein accumulation is enhanced by COP1 but decreased by light. Taken together, EIN3/EIL1 represent a new class of transcriptional regulators along with PIF1 to optimize de-etiolation of Arabidopsis seedlings. Our study highlights the essential role of ethylene in enhancing seedling development and survival through protecting etiolated seedlings against photo-oxidative damage.