Yellow-green Leaf Research Articles

Physiological and Transcriptome Analysis of a Yellow-Green Leaf Mutant in Birch (Betula platyphylla × B. Pendula)

Chlorophyll (Chl)-deficient mutants are ideal materials for the study of Chl biosynthesis, chloroplast development, and photosynthesis. Although the genes encoding key enzymes related to Chl biosynthesis have been well-characterized in herbaceous plants, rice (Oryza sativa L.), Arabidopsis (Arabidopsis thaliana), and maize (Zea mays L.), yellow-green leaf mutants have not yet been fully studied in tree species. In this work, we explored the molecular mechanism of the leaf color formation in a yellow-green leaf mutant (yl). We investigated the differentially expressed genes (DEGs) between yl and control plants (wild type birch (WT) and BpCCR1 overexpression line 11, (C11)) by transcriptome sequencing. Approximately 1163 genes (874 down-regulated and 289 up-regulated) and 930 genes (755 down-regulated and 175 up-regulated) were found to be differentially expressed in yl compared with WT and C11, respectively. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis for DEGs revealed that photosynthesis antenna proteins represent the most significant enriched pathway. The expressions of photosynthesis antenna proteins are crucial to the leaf color formation in yl. We also found that Chl accumulate, leaf anatomical structure, photosynthesis, and growth were affected in yl. Taken together, our results not only provide the difference of phenomenal, physiological, and gene expression characteristics in leaves between yl mutant and control plants, but also provide a new insight into the mutation underlying the chlorotic leaf phenotype in birch.

Rapid mapping of a chlorina mutant gene cn-A1 in hexaploid wheat by bulked segregant analysis and single nucleotide polymorphism genotyping arrays

The yellow–green leaf mutant can be exploited in photosynthesis and plant development research. A Triticum aestivum mutant with the chlorina phenotype, here called B23, was produced by treatment with the chemical mutagen sodium azide. This B23 mutant showed significantly lower chlorophyll content than wild-type Saannong33, and its chloroplast structure was abnormal. All its yield-related traits, except for the number of spikes per plant, were also significantly decreased. Genetic analysis confirmed that the mutant phenotype was controlled by a recessive gene, here designated cn-A1. Using bulked segregant analysis and the wheat 660K single nucleotide polymorphism array, the cn-A1 gene was mapped to chromosome 7AL, and 11 polymorphic markers were developed. Further analysis showed that cn-A1 was located in a 1.1-cM genetic region flanked by Kompetitive allele specific PCR (KASP) markers 660K-7A12 and 660K-7A20, which corresponded to a physical interval of 3.48 Mb in T. aestivum cv. Chinese Spring chromosome 7AL containing 47 predicted genes with high confidence. These results are expected to accelerate the process of cloning the cn-A1 gene and facilitate understanding of the mechanisms underlying chlorophyll metabolism and chloroplast development in wheat.

SiYGL2 Is Involved in the Regulation of Leaf Senescence and Photosystem II Efficiency in Setaria italica (L.) P. Beauv.

A yellow-green leaf mutant was isolated from EMS-mutagenized lines of Setaria italica variety Yugu1. Map-based cloning revealed the mutant gene is a homolog of Arabidopsis thaliana AtEGY1. EGY1 (ethylene-dependent gravitropism-deficient and yellow-green 1) is an ATP-independent metalloprotease (MP) that is required for chloroplast development, photosystem protein accumulation, hypocotyl gravitropism, leaf senescence, and ABA signal response in A. thaliana. However, the function of EGY1 in monocotyledonous C4 plants has not yet been described. The siygl2 mutant is phenotypically characterized by chlorotic organs, premature senescence, and damaged PS II function. Sequence comparisons of the AtEGY1 and SiYGL2 proteins reveals the potential for SiYGL2 to encode a partially functional protein. Phenotypic characterization and gene expression analysis suggested that SiYGL2 participates in the regulation of chlorophyll content, leaf senescence progression, and PS II function. Additionally, our research will contribute to further characterization of the mechanisms regulating leaf senescence and photosynthesis in S. italica, and in C4 plants in general.

Characterization of the Leaf Color Mutant hy and Identification of the Mutated Gene in Chinese Cabbage

Leaf color mutants play an important role in our understanding of chlorophyll biosynthesis and catabolism. In this study, we obtained a yellow-green leaf mutant hy in an ethyl methanesulfonate mutagenized population of chinese cabbage (Brassica rapa ssp. pekinensis). The hy phenotype was controlled by a recessive allele at a single locus. The intrinsic photochemical activity of photosystem II (PSII) is impaired in hy, suggesting that absorbed light energy is not efficiently transferred from the light-harvesting complexes antenna to the PSII reaction centers and dissipated as heat or fluorescence. We measured chlorophyll content and chlorophyll precursors and analyzed the expression of key genes in the chlorophyll synthetic pathway in hy and wild type. The mutation phenotype was consistent with inhibited expression of chlorophyll a oxygenase (CAO) gene in the chlorophyll synthetic pathway. In mutant hy, CAO cDNA was cloned so that a C to T mutation at 1099 bp caused a conserved proline (Pro) to serine (Ser) mutation at the 367th amino acid in C-domain, which changed the secondary structure of CAO protein. We speculate that the mutation amino acid changed in the C-domain may affect the catalytic function in mutant CAO.

Candidate Genes for Yellow Leaf Color in Common Wheat (Triticum aestivum L.) and Major Related Metabolic Pathways according to Transcriptome Profiling.

The photosynthetic capacity and efficiency of a crop depends on the biosynthesis of photosynthetic pigments and chloroplast development. However, little is known about the molecular mechanisms of chloroplast development and chlorophyll (Chl) biosynthesis in common wheat because of its huge and complex genome. Ygm, a spontaneous yellow-green leaf color mutant of winter wheat, exhibits reduced Chl contents and abnormal chloroplast development. Thus, we searched for candidate genes associated with this phenotype. Comparative transcriptome profiling was performed using leaves from the yellow leaf color type (Y) and normal green color type (G) of the Ygm mutant progeny. We identified 1227 differentially expressed genes (DEGs) in Y compared with G (i.e., 689 upregulated genes and 538 downregulated genes). Gene ontology and pathway enrichment analyses indicated that the DEGs were involved in Chl biosynthesis (i.e., magnesium chelatase subunit H (CHLH) and protochlorophyllide oxidoreductase (POR) genes), carotenoid biosynthesis (i.e., β-carotene hydroxylase (BCH) genes), photosynthesis, and carbon fixation in photosynthetic organisms. We also identified heat shock protein (HSP) genes (sHSP, HSP70, HSP90, and DnaJ) and heat shock transcription factor genes that might have vital roles in chloroplast development. Quantitative RT-PCR analysis of the relevant DEGs confirmed the RNA-Seq results. Moreover, measurements of seven intermediate products involved in Chl biosynthesis and five carotenoid compounds involved in carotenoid-xanthophyll biosynthesis confirmed that CHLH and BCH are vital enzymes for the unusual leaf color phenotype in Y type. These results provide insights into leaf color variation in wheat at the transcriptional level.

Genetics and mapping of the novel leaf-colour mutant gene

Leaf colour plays an important role in plant growth and development. In this study, a stably inherited yellow–green leaf mutation, temporarily designated yglw-1, was initially isolated from progenies of wheat (Triticum aestivum L.) cross Bainong58409/Caifumai. The yellow-leaf phenotype could be observed in the yglw-1 mutant during the seedling stage, and then the yellow leaves gradually progressed from the bottom to the top throughout development. Compared with its sister line Cf5019-21 with a normal leaf-colour phenotype, the main agronomic traits of the yglw-1 mutant including spike length, number of kernels per spike and 1000-kernel weight were significantly decreased. Measurement of chlorophyll contents showed that chlorophylls a and b in the third top leaf at the jointing stage and the penultimate leaf and third top leaf at the heading stage were obviously lower in yglw-1 than in Cf5019-21. Genetic analysis indicated that the yellow–green leaf trait was controlled by a single recessive gene. Bulked segregant analysis found that two published simple sequence repeat (SSR) markers and four expressed sequence tag-sequence tagged site (EST-STS) markers were linked to the yglw-1 gene, and BE494262 was the most closely linked marker to yglw-1, at a genetic distance of 2.3 cM. To increase the density of the genetic map, 135 novel SSR markers at a certain distance near the marker BE494262 were developed according to SSR loci detected in the Chinese Spring reference sequence. Of these, nine SSR markers detected polymorphic fragments between the two parents as well as between the contrasting DNA bulks. Finally, the yglw-1 gene was mapped between SSR markers Xhwm1 and Xhwm43 and showed genetic distances 1.9 cM and 23.9 cM on chromosome 2BS. These findings can facilitate candidate-gene prediction and map-based cloning of the yglw-1 gene.

Expression Pattern and Protein Localization of a Yellow-Green Leaf 6 ( YGL6 ) Gene in Rice ( Oryza sativa )

Expression Pattern and Protein Localization of a <i>Yellow-Green Leaf 6</i> ( <i>YGL6</i> ) Gene in Rice ( <i>Oryza sativa</i> )

A single nucleotide mutation of IspF gene involved in the MEP pathway for isoprenoid biosynthesis causes yellow-green leaf phenotype in rice.

We identified IspF gene through yellow-green leaf mutant 505ys in rice. OsIspF was expressed in all tissues detected, and its encoded protein was targeted to the chloroplast. On expression levels of genes in this mutant, OsIspF itself and the genes encoding other enzymes of the MEP pathway and chlorophyll synthase were all up-regulated, however, among eight genes associated with photosynthesis, only psaA, psaN and psbA genes for three reaction center subunits of photosystem obviously changed. Isoprenoids are the most abundant natural compounds in all organisms, which originate from the basic five-carbon units isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP). In plants, IPP and DMAPP are synthesized through two independent pathways, the mevalonic acid pathway in cytoplasm and the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway in plastids. The MEP pathway comprises seven enzymatic steps, in which IspF is the fifth enzyme. So far, no IspF gene has been identified in monocotyledonous plants. In this study, we isolated a leaf-color mutant, 505ys, in rice (Oryza sativa). The mutant displayed yellow-green leaf phenotype, reduced level of photosynthetic pigments, and arrested development of chloroplasts. By map-based cloning of this mutant, we identified OsIspF gene (LOC_Os02g45660) showing significant similarity to IspF gene of Arabidopsis, in which a missense mutation occurred in the mutant, resulting in an amino acid change in the encoded protein. OsIspF gene was expressed in all tissues detected, and its encoded protein was targeted to the chloroplast. Further, the mutant phenotype of 505ys was complemented by transformation with the wild-type OsIspF gene. Therefore, we successfully identified an IspF gene in monocotyledonous plants. In addition, real-time quantitative RT-PCR implied that a positive regulation could exist between the OsIspF gene and the genes encoding other enzymes of the MEP pathway and chlorophyll synthase. At the same time, it also implied that the individual genes involved in the MEP pathway might differentially regulated expression levels of the genes associated with photosynthesis.

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 rice YGL gene encoding an Mg2+-chelatase ChlD subunit is affected by temperature for chlorophyll biosynthesis

Leaf color-related mutants are important materials to study the chlorophyll biosynthesis and chloroplast development. Here, we isolated and characterized a thermosensitive yellow-green leaf mutant, ygl, through mutagenized Japonica rice cultivar Zhonghua11 by EMS. The mutant showed yellow-green leaves only at the seedling stage. Genetic and molecular analyses uncovered that YGL encode an Mg2+-chelatase ChlD subunit, which was a new allele of Chl1/YGL7. Quantitative PCR and GUS staining showed that the YGL transcripts expressed in all tested organs and subcellular localization detected YGL protein in the chloroplasts. The mutant displayed yellow-green leaves at 20°C and normal green leaves at 34°C during the seedling stage. Transcript level of YGL in the ygl mutant was significantly reduced at 20°C, and increased at 34°C compared with the wild-type plant. Furthermore, the expression of chlorophyll biosynthesis and chloroplast development related genes were influenced by the mutation of YGL at different temperature. These findings suggested that the YGL gene not only play a key role in chlorophyll biosynthesis, but is affected at transcript level by temperature in rice.

Identification and genetic mapping of a novel incompletely dominant yellow leaf color gene, Y1718, on chromosome 2BS in wheat

The yellow-green leaf color mutant (Ygm) is a spontaneous mutant derived from the common wheat (Triticum aestivum L.) cultivar Xinong1718. Genetic analysis has shown that a novel single incompletely dominant gene (Y1718) is responsible for the yellow leaf color phenotype. The progeny of Ygm exhibit three distinct leaf color phenotypes, i.e., yellow (Y), yellow-green (Yg), and normal green (G). Y plants have yellow-green leaves in the seedling stage, which become yellow or a strong gold-yellow in the booting stage, with dwarfism and thin tillers until the flowering stage, and underdeveloped thylakoid membranes without well-structured grana in the chloroplasts. Yg plants always have a yellow-green phenotype with a number of well-structured grana that are loosely connected with stroma lamellae in the chloroplasts, where their main agronomic traits are the same as Xinong1718 and G plants, but the seed yield is low. Compared with Xinong1718 and G plants, Y and Yg plants had much lower chlorophyll (Chl) a, Chl b, and carotenoid contents in the booting stage. Molecular analysis using an F2 population and F2:3 lines derived from a cross of Yg and Shannong1 indicated that the Y1718 gene is located on chromosome 2BS, where it is flanked by the simple sequence repeat marker Xwmc25 and expressed sequence tag-sequence tagged sites marker BE498358 at genetic distances of 1.7 and 4.0 cM, respectively. Our results facilitate the fine mapping and gene cloning of Y1718 to explore chlorophyll synthesis, metabolism, and development in wheat.

Mutation in Mg-Protoporphyrin IX Monomethyl Ester Cyclase Decreases Photosynthesis Capacity in Rice.

In photosynthesis, the pigments chlorophyll a/b absorb light energy to convert to chemical energy in chloroplasts. Though most enzymes of chlorophyll biosynthesis from glutamyl-tRNA to chlorophyll a/b have been identified, the exact composition and regulation of the multimeric enzyme Mg-protoporphyrin IX monomethyl ester cyclase (MPEC) is largely unknown. In this study, we isolated a rice pale-green leaf mutant m167 with yellow-green leaf phenotype across the whole lifespan. Chlorophyll content decreases 43–51% and the granal stacks of chloroplasts becomes thinner in m167. Chlorophyll fluorescence parameters, including Fv/Fm (the maximum quantum efficiency of PSII) and quantum yield of PSII (Y(II)), were lower in m167 than those in wild type plants (WT), and photosynthesis rate decreases 40% in leaves of m167 mutant compared with WT plants, which lead to yield reduction in m167. Genetic analysis revealed that yellow-green leaf phenotype of m167 is controlled by a single recessive genetic locus. By positional cloning, a single mutated locus, G286A (Alanine 96 to Threonine in protein), was found in the coding sequence of LOC_Os01g17170 (Rice Copper Response Defect 1, OsCRD1), encoding a putative subunit of MPEC. Expression profile analysis demonstrated that OsCRD1 is mainly expressed in green tissues of rice. Sequence alignment analysis of CRD1 indicated that Alanine 96 is very conserved in all green plants and photosynthetic bacteria. OsCRD1 protein mainly locates in chloroplast and the point mutation A96T in OsCRD1 does not change its location. Therefore, Alanine96 of OsCRD1 might be fundamental for MPEC activity, mutation of which leads to deficiency in chlorophyll biosynthesis and chloroplast development and decreases photosynthetic capacity in rice.

Heme oxygenase 1 defects lead to reduced chlorophyll in Brassica napus.

We previously described a Brassica napus chlorophyll-deficient mutant (ygl) with yellow-green seedling leaves and mapped the related gene, BnaC.YGL, to a 0.35cM region. However, the molecular mechanisms involved in this chlorophyll defect are still unknown. In this study, the BnaC07.HO1 gene (equivalent to BnaC.YGL) was isolated by the candidate gene approach, and its function was confirmed by genetic complementation. Comparative sequencing analysis suggested that BnaC07.HO1 was lost in the mutant, while a long noncoding-RNA was inserted into the promoter of the homologous gene BnaA07.HO1. This insert was widely present in B. napus cultivars and down-regulated BnaA07.HO1 expression. BnaC07.HO1 was highly expressed in the seedling leaves and encoded heme oxygenase 1, which was localized in the chloroplast. Biochemical analysis showed that BnaC07.HO1 can catalyze heme conversion to form biliverdin IXα. RNA-seq analysis revealed that the loss of BnaC07.HO1 impaired tetrapyrrole metabolism, especially chlorophyll biosynthesis. According, the levels of chlorophyll intermediates were reduced in the ygl mutant. In addition, gene expression in multiple pathways was affected in ygl. These findings provide molecular evidences for the basis of the yellow-green leaf phenotype and further insights into the crucial role of HO1 in B. napus.

Effect of mixed salt stress on malondialdehyde, proteins and antioxidant enzymes of Leymus chinensis in three leaf colors

The mixed salt stress is common in nature. Salt stressalways affects plant growth. Different plant species have differentadaptive capacity to salty soils. Leymus chinensis is an herbaceous plantwith different leaf colors. However, little research was conducted toexplore the different tolerance mechanisms to salt stress among thethree different leaf colour genotypes of Leymus chinensis (grey green,transitional color, yellow green). Pot experiments for Leymus chinensisin three leaf colors were conducted under mixed salt treatments in2010. Malondialdehyde (MDA) and protein concentrations, and theactivity of various antioxidant enzymes [i.e., superoxide dismutase(SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase(GR), dehydroascorbate reductase (DHAR) and monodehydroascorbatereductase (MDHAR)] were determined and comparedamong the three leaf color genotypes of Leymus chinensis. The concentrationsof MDA and protein, and the activity of antioxidant enzymesshowed an increasing trend with increasing pHs in almost allthree leaf colors, and all of them became highest when salt stress andpH values were also highest. Moreover, antioxidant enzymes werethe highest in the grey-green leaf color, and the lowest in the yellowgreen leaf color after exposure to the same pH treatment. The resultssuggested that all three leaf colors of Leymus chinensis were tolerantto salt stress, and the salt-tolerance declined according to the orderof grey green > transitional color > yellow green of Leymus chinensis.This study can give us a better understanding of the intra-speciesadaptation to mixed salt soils.

Map-based cloning and characterization of the novel yellow-green leaf gene ys83 in rice (Oryza sativa)

Leaf-color mutants have been extensively studied in rice, and many corresponding genes have been identified up to now. However, leaf-color mutation mechanisms are diverse and still need further research through identification of novel genes. In the present paper, we isolated a leaf-color mutant, ys83, in rice (Oryza sativa). The mutant displayed a yellow-green leaf phenotype at seedling stage, and then slowly turned into light-green leaf from late tillering stage. In its yellow leaves, photosynthetic pigment contents significantly decreased and the chloroplast development was retarded. The mutant phenotype was controlled by a recessive mutation in a nuclear gene on the short arm of rice chromosome 2. Map-based cloning and sequencing analysis suggested that the candidate gene was YS83 (LOC_Os02g05890) encoding a protein containing 165 amino acid residues. Gene YS83 was expressed in a wide range of tissues, and its encoded protein was targeted to the chloroplast. In the mutant, a T-to-A substitution occurred in coding sequence of gene YS83, which caused a premature translation of its encoded product. By introduction of the wild-type gene, the ys83 mutant recovered to normal green-leaf phenotype. Taken together, we successfully identified a novel yellow-green leaf gene YS83. In addition, number of productive panicles per plant and number of spikelets per panicle only reduced by 6.7% and 7.6%, respectively, meanwhile its seed setting rate and 1000-grain weight (seed size) were not significantly affected in the mutant, so leaf-color mutant gene ys83 could be used as a trait marker gene in commercial hybrid rice production.

Comparative Proteomic and Physiological Analysis Reveals the Variation Mechanisms of Leaf Coloration and Carbon Fixation in a Xantha Mutant of Ginkgo biloba L.

Yellow-green leaf mutants are common in higher plants, and these non-lethal chlorophyll-deficient mutants are ideal materials for research on photosynthesis and plant development. A novel xantha mutant of Ginkgo biloba displaying yellow-colour leaves (YL) and green-colour leaves (GL) was identified in this study. The chlorophyll content of YL was remarkably lower than that in GL. The chloroplast ultrastructure revealed that YL had less dense thylakoid lamellae, a looser structure and fewer starch grains than GL. Analysis of the photosynthetic characteristics revealed that YL had decreased photosynthetic activity with significantly high nonphotochemical quenching. To explain these phenomena, we analysed the proteomic differences in leaves and chloroplasts between YL and GL of ginkgo using two-dimensional gel electrophoresis (2-DE) coupled with MALDI-TOF/TOF MS. In total, 89 differential proteins were successfully identified, 82 of which were assigned functions in nine metabolic pathways and cellular processes. Among them, proteins involved in photosynthesis, carbon fixation in photosynthetic organisms, carbohydrate/energy metabolism, amino acid metabolism, and protein metabolism were greatly enriched, indicating a good correlation between differentially accumulated proteins and physiological changes in leaves. The identifications of these differentially accumulated proteins indicates the presence of a specific different metabolic network in YL and suggests that YL possess slower chloroplast development, weaker photosynthesis, and a less abundant energy supply than GL. These studies provide insights into the mechanism of molecular regulation of leaf colour variation in YL mutants.

The catalytic subunit of magnesium-protoporphyrin IX monomethyl ester cyclase forms a chloroplast complex to regulate chlorophyll biosynthesis in rice.

YGL8 has the dual functions in Chl biosynthesis: one as a catalytic subunit of MgPME cyclase, the other as a core component of FLU-YGL8-LCAA-POR complex in Chl biosynthesis. Magnesium-protoporphyrin IX monomethyl ester (MgPME) cyclase is an essential enzyme involved in chlorophyll (Chl) biosynthesis. However, its roles in regulating Chl biosynthesis are not fully explored. In this study, we isolated a rice mutant yellow-green leaf 8 (ygl8) that exhibited chlorosis phenotype with abnormal chloroplast development in young leaves. As the development of leaves, the chlorotic plants turned green accompanied by restorations in Chl content and chloroplast ultrastructure. Map-based cloning revealed that the ygl8 gene encodes a catalytic subunit of MgPME cyclase. The ygl8 mutation caused a conserved amino acid substitution (Asn182Ser), which was related to the alterations of Chl precursor content. YGL8 was constitutively expressed in various tissues, with more abundance in young leaves and panicles. Furthermore, we showed that expression levels of some nuclear genes associated with Chl biosynthesis were affected in both the ygl8 mutant and YGL8 RNA interference lines. By transient expression in rice protoplasts, we found that N-terminal 40 amino acid residues were enough to localize the YGL8 protein to chloroplast. In vivo experiments demonstrated a physical interaction between YGL8 and a rice chloroplast protein, low chlorophyll accumulation A (OsLCAA). Moreover, bimolecular fluorescence complementation assays revealed that YGL8 also interacted with the other two rice chloroplast proteins, viz. fluorescent (OsFLU1) and NADPH:protochlorophyllide oxidoreductase (OsPORB). These results provide new insights into the roles of YGL8, not only as a subunit with catalytic activity, but as a core component of FLU-YGL8-LCAA-POR complex required for Chl biosynthesis.

Map-based cloning and functional analysis of YGL8, which controls leaf colour in rice (Oryza sativa).

BackgroundAs the indispensable part of plant, leaf blade mainly functions as the production workshops where organic substance is produced by photosynthesis. Leaf colour mutation is a genetic phenomenon that has a high frequency and is easily identified. The mutations always exhibit negative impact on the development of plants in any of the different stages of growth. Up to now, numerous genes involved in leaf colour mutations have been cloned.ResultsIn this study, a yellow-green leaf mutant, yellow-green leaf 8 (ygl8), with stable genetic phenotype, has been screened out in the progeny of an excellent indica restorer line Jinhui 10 with seeds treated by EMS. The levels of Chl a, Chl b and total chlorophyll were significantly lower in ygl8 than those in the WT throughout the whole growth period, while no clear change was noted in the Chl a/b ratio. Transmission electron microscopy demonstrated that the lamellae were clearly intumescent and intricately stacked in ygl8. Furthermore, compared with those of the WT, the stomatal conductance, intercellular CO2 concentration, photosynthetic rate and transpiration rate of ylg8 were all significantly lower. Map-based cloning results showed that Loc_Os01g73450, encoding a chloroplast-targeted UMP kinase, corresponded to Ygl8 and played an important role in regulating leaf colour in rice (Oryza sativa). Complementation of ygl8 with the WT DNA sequence of Loc_Os01g73450 led to restoration of the normal phenotype, and transgenic RNA interference plants showed a yellow-green colour. Analysis of the spatial and temporal expression of Ygl8 indicated that it was highly expressed in leaf blades and weakly expressed in other tissues. qRT-PCR also showed that the expression levels of the major Photosystem I core subunits plastome-encoded PsaA, PsaB and PsbC were significantly reduced in ygl8. The expression levels of nuclear-encoded gene involved in Chl biosynthesis HEMC, HEME, and PORA were also decreased when compared with the wild-type.ConclusionsIndependent of Chl biosynthesis and photosystem, YGL8 may affect the structure and function of chloroplasts grana lamellae by regulating plastid genome encoded thylakoid membrane constitutive gene expression and indirectly influences Chl biosynthesis.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0821-5) contains supplementary material, which is available to authorized users.

Genetics and fine mapping of a yellow-green leaf gene (ygl-1) in cabbage (Brassica oleracea var. capitata L.)

Cabbage (Brassica oleracea var. capitata L.) is one of the most popular cultivated vegetables worldwide. Cabbage has rich phenotypic diversity, including plant height, head shape, head color, leaf shape and leaf color. Leaf color plays an important role in cabbage growth and development. At present, there are few reports on fine mapping of leaf color mutants in B. oleracea. In this study, a naturally occurring yellow-green leaf cabbage mutant (YL-1), derived from the self-pollinated progenies of the hybrid ‘Hosom’, was used for inheritance analysis and gene mapping. Segregation populations including F2 and BC1 were generated from the cross of two inbred lines, YL-1 and 01–20. Genetic analysis with the F2 and BC1 populations demonstrated that the yellow-green leaf color was controlled by a single recessive nuclear gene, ygl-1. Insertion–deletion (InDel) markers, designed based on the parental re-sequencing data, were used for the preliminary mapping with BSA (bulked segregant analysis) method. A genetic map constructed with 15 InDels indicated that ygl-1 was located on chromosome C01. The ygl-1 gene is flanked by InDel markers ID2 and M8, with genetic distances of 0.4 cM and 0.35 cM, respectively. The interval distance between two markers is 167 kb. Thus, it enables us to locate the ygl-1 gene for the first time in B. oleracea. This study lays the foundation for candidate gene prediction and ygl-1gene cloning.

YGL9, encoding the putative chloroplast signal recognition particle 43 kDa protein in rice, is involved in chloroplast development

The nuclear-encoded light-harvesting chlorophyll a/b-binding proteins (LHCPs) are specifically translocated from the stroma into the thylakoid membrane through the chloroplast signal recognition particle (cpSRP) pathway. The cpSRP is composed of a cpSRP43 protein and a cpSRP54 protein, and it forms a soluble transit complex with LHCP in the chloroplast stroma. Here, we identified the YGL9 gene that is predicted to encode the probable rice cpSRP43 protein from a rice yellow-green leaf mutant. A phylogenetic tree showed that an important conserved protein family, cpSRP43, is present in almost all green photosynthetic organisms such as higher plants and green algae. Sequence analysis showed that YGL9 comprises a chloroplast transit peptide, three chromodomains and four ankyrin repeats, and the chromodomains and ankyrin repeats are probably involved in protein-protein interactions. Subcellular localization showed that YGL9 is localized in the chloroplast. Expression pattern analysis indicated that YGL9 is mainly expressed in green leaf sheaths and leaves. Quantitative real-time PCR analysis showed that the expression levels of genes associated with pigment metabolism, chloroplast development and photosynthesis were distinctly affected in the ygl9 mutant. These results indicated that YGL9 is possibly involved in pigment metabolism, chloroplast development and photosynthesis in rice.