Phylogeny of Trigonotis in China-with a special reference to its nutlet morphology and plastid genome

The genus Trigonotis comprises nearly 60 species mainly distributed in East and Southeast Asia.China has the largest number of Trigonotis species in the world,with a total of 44 species,of which 38 are endemic.Nutlet morphology is useful for the taxonomic delimitation of Trigonotis.However,there are still controversial circumscriptions of nutlet shape in some species.In previous studies,interspecies phylogenetic relationships were inferred using few DNA markers and very few taxa,which possibly led to erroneous or incomplete conclusions.In this study,the nutlet morphology of 39 Trigonotis taxa and the characteristics of 34 complete chloroplast genomes(29 taxa)were investigated and analyzed.Then,the phylogenetic relationships were discussed within this genus based on complete chloroplast genomes.To the best of our knowledge,this study is the first comprehensive analysis of nutlet morphology and complete chloroplast genome of Trigonotis.Based on nutlet morphology,Trigonotis can be divided into two groups:Group 1,hemispherical or oblique tetrahedron with carpopodiums,and Group 2,inverted tetrahedron without carpopodiums.The chloroplast genome of Trigonotis exhibited a typical quadripartite structure,including 84-86 protein-coding,37 transfer RNA,and 8 ribosomal RNA genes,with a total length of 147,247-148,986 bp.Genes in the junctions were well conserved in Trigonotis,similar to those in other Boraginaceae s.str.species.Furthermore,Trigonotis chloroplast genomes showed relatively high diversity,with more conserved genic regions than intergenic regions;in addition,we detected 14 hot spots(Pi>0.005)in non-coding regions.Phylogenetic analyses based on chloroplast genome data identified highly resolved relationships between Trigonotis species.Specifically,Trigonotis was divided into two clades with strong support:one clade included species with hemispherical or oblique tetrahedron nutlets with carpopodiums and bracts,whereas the other clade included species with inverted tetrahedron nutlets without carpopodiums or bracts.Our results may inform future taxonomic,phylogenetic,and evolutionary studies on Boraginaceae.

Plastid phylogenomics and biogeography of the medicinal plant lineage Hyoscyameae(Solanaceae)

The cosmopolitan family Solanaceae,which originated and first diversified in South America,is economically important.The tribe Hyoscyameae is one of the three clades in Solanaceae that occurs outside of the New World;Hyoscyameae genera are distributed mainly in Europe and Asia,and have centers of species diversity in the Qinghai-Tibet Plateau and adjacent regions.Although many phylogenetic studies have focused on Solanaceae,the phylogenetic relationships within the tribe Hyoscyameae and its biogeographic history remain obscure.In this study,we reconstructed the phylogeny of Hyoscyameae based on whole chloroplast genome data,and estimated lineage divergence times according to the newly reported fruit fossil from the Eocene Patagonia,Physalis infinemundi,the earliest known fossil of Solanaceae.We reconstructed a robust phylogeny of Hyoscyameae that reveals the berry fruit-type Atropa is sister to the six capsule-bearing genera(Hyoscyameae sensu stricto),Atropanthe is sister to the clade(Scopolia,Physochlaina,Przewalskia),and together they are sister to the robustly supported AnisoduseHyoscyamus clade.The stem age of Hyoscyameae was inferred to be in the Eocene(47.11 Ma,95%HPD:36.75e57.86 Ma),and the crown ages of Hyoscyameae sensu stricto were estimated as the early Miocene(22.52 Ma,95%HPD:15.19e30.53 Ma),which shows a close correlation with the rapid uplift of the Qinghai-Tibet Plateau at the Paleogene/Neogene boundary.Our results provide insights into the phylogenetic relationships and the history of the biogeographic diversification of the tribe Hyoscyameae,as well as plant diversification on the Qinghai-Tibet Plateau.

Occurrence and light response of residual plastid genes in a Euglena gracilis bleached mutant strain OflB2

Euglena gracilis is a unicellular green eukaryotic microalga that features characteristics of both plants and animals.The photosynthetic function of its chloroplast is easily lost under stress resulting in bleached mutants,while the physiological role of their residual plastid DNAs remains unclear.In this study,we obtained five bleached mutants by ofloxacin(Ofl)treatment,identified 12 residual plastid genes in five bleached mutants,and determined the mRNA levels in the wild type E.gracilis(WT)and one bleached mutant(OflB2)under dark and light stimulation conditions by quantitative reverse transcribed PCR(qRTPCR).Results show that the expression of all selected plastid genes in both WT and OflB2 mutant did not change significantly in darkness,while their responses to light stimulation were different.Under the light stimulation conditions,half of the genes did not change significantly,while most of the other genes were down-regulated in OflB2 mutant and up-regulated in WT.Therefore,the bleached mutant retains part of the plastid genome and the plastid relic is responsive to light.Our research will help to understand the functions of residual plastid DNA and evolution of chloroplasts.

Construction of Lactuca sativa Plastid Transformation Vector and High-level Expression of gfp Gene in Escherichia coli

Using genomic DNA of bolting-tolerant lettuce as a template,flanking fragments of lettuce plastid rpo A gene were amplified and cloned by PCR. Targeting the sites of these two fragments,homologous recombinant fragments of exogenous gene were integrated to construct lettuce plastid expression vector p Brpo AGFP,which harbored the expression cassette Prrn-gfp-aad A-Tpsb A. The results showed that the amplified flanking fragments were 1.2 and 1.1 kb in size. After sequencing,restriction digestion,ligation and transformation,lettuce plastid expression vector containing expression cassette Prrn-gfp-aad A-Tpsb A was constructed and confirmed by SDS-PAGE electrophoresis. The results of SDS-PAGE electrophoresis indicated that gfp gene was efficiently expressed under the regulation of plasmid specific promoter Prrn and terminator Tpsb A. GFP accounted for 45. 6% of total soluble proteins; inclusion bodies accounted for 47.5 % of bacterial proteins,which reached relatively high expression levels. The construction of lettuce plastid expression vector p Brpo A-GFP laid a solid foundation for establishment of subsequent lettuce plastid transformation system and genetic improvement of lettuce using various functional genes.

The Potential of DNA Barcode-Based Delineation Using Seven Putative Candidate Loci of the Plastid Region in Inferring Molecular Diversity of Cowpea at Sub-Species Level

The novelty and suitability of the mitochondrial gene CO1 in DNA barcoding as a reliable identification tool in animal species are undisputed. This is attributed to its standardized sequencing segment of the mitochondrial cytochrome c oxidase-1 gene (CO1) which has the necessary universality and variability making it a generally acceptable barcode region. CO1 is a haploid single locus that is uniparentally-inherited. Protein-coding regions are present in high-copy numbers making it an ideal barcode. The mitochondrial oxidase subunit I (COI) gene is a robust barcode with a suitable threshold for delineating animals and is not subject to drastic length variation, frequent mononucleotide repeats or microinversions. However, a low nucleotide substitution rate of plant mitochondrial genome [mtDNA] precludes the use of CO1 as a universal plant DNA barcode and makes the search for alternative barcode regions necessary. Currently, there exists no universal barcode for plants. The plastid region reveals leading candidate loci as appropriate DNA barcodes yet to be explored in biodiversity studies in Kenya. Four of these plastid regions are portions of coding genes (matK, rbcL, rpoB, and rpoC1), and three noncoding spacers (atpF-atpH, trnH-psbA, and psbK-psbL) which emerge as ideal candidate DNA loci. While different research groups propose various combinations of these loci, there exists no consensus;the lack thereof impedes progress in getting a suitable universal DNA barcode. Little research has attempted to investigate and document the applicability and extend of effectiveness of different DNA regions as barcodes to delineate cowpea at subspecies level. In this study we sought to test feasibility of the seven putative candidate DNA loci singly and in combination in order to establish a suitable single and multi-locus barcode regions that can have universal application in delineating diverse phylogeographic groups of closely related Kenyan cowpea variants. In this study, our focus was based on genetic parameters including analyses of intra- and infra-specific genetic divergence based on intra- and infra-specific K2P distances;calculation of Wilcoxon signed rank tests of intra-specific divergence among loci and coalescence analyses to delineate independent genetic clusters. Knowledge of DNA candidate loci that are informative will reveal the suitability of DNA barcoding as a tool in biodiversity studies. Results of this study indicate that: matK, trnH-psbA, psbK-psbL, and rbcL are good barcodes for delineating intra and infraspecific distances at single loci level. However, among the combinations, matK + trnH-psbA, rpoB + atpF-atpH + matK are the best barcodes in delineating cowpea subvariants. rbcL gene can be a suitable barcode marker at single locus level, but overall, multi locus approach appears more informative than single locus approach. The present study hopes to immensely contribute to the scanty body of knowledge on the novelty of DNA barcoding in cataloguing closely related cowpea variants at molecular level and hopes to open up future research on genomics and the possibility of use of conserved regions within DNA in inferring phylogenetic relationships among Kenyan cowpea variants.

A truncated hepatitis E virus ORF2 protein expressed in tobacco plastids is immunogenic in mice

瞄准：表示 23-ku pE2 到花费有效地，肝炎 E 病毒(HEV ) 的 3'-portion 包括的 E2 碎片编码的最有希望的子单元疫苗打开读物框架 2 (ORF2 ) 在烟草的质体(Nicotiana 烟 cv。SR1 ) ，在质体调查 transgene 表示和 pE2 累积，并且评估反在老鼠的导出质体的 pE2 的遗传因子的效果。方法：包含米饭 psbA 倡导者驾驶的 E2 碎片的指向质体的向量 pRB94-E2 被构造。在进烟草质体的交货之上，这构造能在质体染色体在 psaB-trnfM 和 trnG-psbC 碎片开始相应再结合，并且导致在二碎片之间插入的 transgene。pRB94-E2 与一个 biolistic 粒子轰炸方法被交付，并且转变质体的工厂被获得在补充 spectinomycin 的媒介上跟随炮轰的叶纸巾的新生。改革工厂的 Transplastomic 地位被 PCR 和南部的污点分析证实， transgene 表示被北污点分析调查，并且 pE2 的累积被 ELISA 测量。而且，蛋白浸出物被用来使老鼠免疫，并且在使免疫的老鼠的浆液样品的 pE2 反应的抗体的存在被 ELISA 学习。结果：PCR 和南部的污点分析证实的 Transplastomic 线能活跃地抄录 E2 mRNA。pE2 多肽象 13.27 microg/g 一样高被积累到水平新鲜叶子。pE2 能刺激使免疫的老鼠产生 pE2 特定的抗体。结论：HEV-E2 碎片能被插入到质体染色体，导出的 recombinant pE2 抗原是在老鼠遗传因子的反。因此，质体可以是为 HEV 疫苗的划算的生产的新奇来源。

Plastid KEA-type cation/H+ antiporters are required for vacuolar protein trafficking in Arabidopsis

Arabidopsis plastid antiporters KEA1 and KEA2are critical for plastid development, photosynthetic efficiency, and plant development.Here, we show that KEA1 and KEA2 are involved in vacuolar protein trafficking. Genetic analyses found that the kea1 kea2 mutants had short siliques, small seeds, and short seedlings. Molecular and biochemical assays showed that seed storage proteins were missorted out of the cell and the precursor proteins were accumulated in kea1 kea2. Protein storage vacuoles(PSVs) were smaller in kea1 kea2. Further analyses showed that endosomal trafficking in kea1 kea2 was compromised. Vacuolar sorting receptor 1(VSR1) subcellular localizations, VSR–cargo interactions, and p24 distribution on the endoplasmic reticulum(ER) and Golgi apparatus were affected in kea1 kea2. Moreover, plastid stromule growth was reduced and plastid association with the endomembrane compartments was disrupted in kea1 kea2. Stromule growth was regulated by the cellular pH and K+homeostasis maintained by KEA1 and KEA2. The organellar pH along the trafficking pathway was altered in kea1 kea2. Overall, KEA1 and KEA2 regulate vacuolar trafficking by controlling the function of plastid stromules via adjusting pH and K+homeostasis.

Tetrapyrrole biosynthesis pathway regulates plastid-to-nucleus signaling by controlling plastid gene expression in plants

Plastid-to-nucleus retrograde signaling coordinates nuclear gene expression with chloroplast developmental status and is essential for the photoautotrophic lifestyle of plants.Previous studies have established that tetrapyrrole biosynthesis(TPB)and plastid gene expression(PGE)play essential roles in plastid retrograde signaling during early chloroplast biogenesis;however,their functional relationship remains unknown.In this study,we generated a series of rice TPB-related gun(genome uncoupled)mutants and systematically analyzed their effects on nuclear and plastid gene expression under normal conditions or when subjected to treatments with norflurazon(NF;a noncompetitive inhibitor of carotenoid biosynthesis)and/or lincomycin(Lin;a specific inhibitor of plastid translation).We show that under NF treatment,expression of plastid-encoded polymerase(PEP)-transcribed genes is significantly reduced in the wild type but is derepressed in the TPB-related gun mutants.We further demonstrate that the derepressed expression of PEPtranscribed genes may be caused by increased expression of the PEP core subunit and nuclear-encoded sigma factors and by elevated copy numbers of plastid genome per haploid genome.In addition,we show that expression of photosynthesis-associated nuclear genes(PhANGs)and PEP-transcribed genes is correlated in the rice TPB-related gun mutants,with or without NF or Lin treatment.A similar correlation between PhANGs and PGE is also observed in the Arabidopsis gun4 and gun5 mutants.Moreover,we show that increased expression of PEP-transcribed plastid genes is necessary for the gun phenotype in NF-treated TPB-related gun mutants.Further,we provide evidence that these TPB-related GUN genes act upstream of GUN1 in the regulation of retrograde signaling.Taken together,our results suggest that the TPB-related GUN genes control retrograde plastid signaling by regulating the PGE-dependent retrograde signaling pathway.

Heteromerization of short-chain trans-prenyltransferase controls precursor allocation within a plastidial terpenoid network

Terpenes are the largest and most diverse class of plant specialized metabolites.Sesterterpenes(C25),which are derived from the plastid methylerythritol phosphate pathway,were recently characterized in plants.In Arabidopsis thaliana,four genes encoding geranylfarnesyl diphosphate synthase(GFPPS)(AtGFPPS1 to 4)are responsible for the production of GFPP,which is the common precursor for sesterterpene biosynthesis.However,the interplay between sesterterpenes and other known terpenes remain elusive.Here,we first provide genetic evidence to demonstrate that GFPPSs are responsible for sesterterpene production in Arabidopsis.Blockage of the sesterterpene pathway at the GFPPS step increased the production of geranylgeranyl diphosphate(GGPP)-derived terpenes.Interestingly,co-expression of sester TPSs in GFPPSOE(overexpression)plants rescued the phenotypic changes of GFPPS-OE plants by restoring the endogenous GGPP.We further demonstrated that,in addition to precursor(DMAPP/IPP)competition by GFPPS and GGPP synthase(GGPPS)in plastids,GFPPS directly decreased the activity of GGPPS through protein-protein interaction,ultimately leading to GGPP deficiency in planta.Our study provides a new regulatory mechanism of the plastidial terpenoid network in plant cells.

Complete protection from Henosepilachna vigintioctopunctata by expressing long double-stranded RNAs in potato plastids

RNA interference(RNAi)has emerged as a powerful technology for pest management.Previously,we have shown that plastid-mediated RNAi(PM-RNAi)can be utilized to control the Colorado potato beetle,an insect pest in the Chrysomelidae family;however,whether this technology is suitable for controlling pests in the Coccinellidae remained unknown.The coccinellid 28-spotted potato ladybird(Henosepilachna vigintioctopunctata;HV)is a serious pest of solanaceous crops.In this study,we identified three efficient target genes(β-Actin,SRP54,and SNAP)for RNAi using in vitro double-stranded RNAs(dsRNAs)fed to HV,and found that dsRNAs targetingβ-Actin messenger RNA(dsACT)induced more potent RNAi than those targeting the other two genes.We next generated transplastomic and nuclear transgenic potato(Solanum tuberosum)plants expressing HV dsACT.Long dsACT stably accumulated to up to 0.7%of the total cellular RNA in the transplastomic plants,at least three orders of magnitude higher than in the nuclear transgenic plants.Notably,the transplastomic plants also exhibited a significantly stronger resistance to HV,killing all larvae within 6 d.Our data demonstrate the potential of PM-RNAi as an efficient pest control measure for HV,extending the application range of this technology to Coccinellidae pests.

The Translational Apparatus of Plastids and Its Role in Plant Development

Chloroplasts （plastids） possess a genome and their own machinery to express it. Translation in plastids occurs on bacterial-type 70S ribosomes utilizing a set of tRNAs that is entirely encoded in the plastid genome. In recent years, the components of the chloroplast translational apparatus have been intensely studied by proteomic approaches and by reverse genetics in the model systems tobacco （plastid-encoded components） and Arabidopsis （nucleus-encoded components）. This work has provided important new insights into the structure, function, and biogenesis of chloroplast ribosomes, and also has shed fresh light on the molecular mechanisms of the translation process in plastids. In addition, mutants affected in plastid translation have yielded strong genetic evidence for chloroplast genes and gene products influencing plant develop- ment at various levels, presumably via retrograde signaling pathway（s）. In this review, we describe recent progress with the functional analysis of components of the chloroplast translational machinery and discuss the currently available evidence that supports a significant impact of plastid translational activity on plant anatomy and morphology.

Carotenoid Metabolism in Plants： The Role ol Plastids

Carotenoids are indispensable to plants and critical in human diets. Plastids are the organelles for carotenoid biosynthesis and storage in plant cells. They exist in various types, which include proplastids, etioplasts, chloroplasts, amyloplasts, and chromoplasts. These plastids have dramatic differences in their capacity to synthesize and sequester carotenoids. Clearly, plastids play a central role in governing carotenogenic activity, carotenoid stability, and pigment diversity. Understanding of carotenoid metabolism and accumulation in various plastids expands our view on the multifaceted regulation of carotenogenesis and facilitates our efforts toward developing nutrient-enriched food crops. In this review, we provide a comprehensive overview of the impact of various types of plastids on carotenoid biosynthesis and accumulation, and discuss recent advances in our understanding of the regulatory control of carotenogenesis and metabolic engineering of carotenoids in light of plastid types in plants.

Arabidopsis FtsZ2-1 and FtsZ2-2 Are Functionally Redundant, But FtsZ-Based Plastid Division Is Not Essential for Chloroplast Partitioning or Plant Growth and Development

FtsZ1 and FtsZ2 are phylogenetically distinct families of FtsZ in plants that co-localize to mid-plastid rings and facilitate division of chloroplasts. In plants, altered levels of either FtsZ1 or FtsZ2 cause dose-dependent defects in chloroplast division; thus, studies on the functional relationship between FtsZgenes require careful manipulation of FtsZ levels in vivo. To define the functional relationship between the two FtsZ2 genes in Arabidopsis thaliana, FtsZ2-1 and FtsZ2-2, we expressed FtsZ2-1 in an ftsZ2-2 null mutant, and vice versa, and determined whether the chloroplast division defects were rescued in plants expressing different total levels of FtsZ2. Full rescue was observed when either the FtsZ2-1 or FtsZ2-2 level approximated total FtsZ2 levels in wild-type （WT）. Additionally, FtsZ2-2 interacts with ARC6, as shown previously for FtsZ2- 1. These data indicate that FtsZ2-1 and FtsZ2-2 are functionally redundant for chloroplast division in Arabidopsis. To rigorously validate the requirement of each FtsZ family for chloroplast division, we replaced FtsZ1 with FtsZ2 in vivo, and vice versa, while maintaining the FtsZ level in the transgenic plants equal to that of the total level in WT. Chloroplast division defects were not rescued, demonstrating conclusively that FtsZ1 and FtsZ2 are non-redundant for maintenance of WT chloroplast numbers. Finally, we generated ftsZtriple null mutants and show that plants completely devoid of FtsZ protein are viable and fertile. As plastids are presumably essential organelles, these findings suggest that an FtsZ-independent mode of plastid partitioning may occur in higher plants.

Plastid Signals and the Bundle Sheath： Mesophyll Development in Reticulate Mutants

The development of a plant leaf is a meticulously orchestrated sequence of events producing a complex organ comprising diverse cell types. The reticulate class of leaf variegation mutants displays contrasting pigmentation between veins and interveinal regions due to specific aberrations in the development of mesophyll cells. Thus, the reticulate mutants offer a potent tool to investigate cell-type-specific developmental processes. The discovery that most mutants are affected in plastid-localized, metabolic pathways that are strongly expressed in vasculature-associated tis- sues implicates a crucial role for the bundle sheath and their chloroplasts in proper development of the mesophyll cells. Here, we review the reticulate mutants and their phenotypic characteristics, with a focus on those in Arabidopsis thali- ana. Two alternative models have been put forward to explain the relationship between plastid metabolism and meso- phyll cell development, which we call here the supply and the signaling hypotheses. We critically assess these proposed models and discuss their implications for leaf development and bundle sheath function in C3 species. The characteriza- tion of the reticulate mutants supports the significance of plastid retrograde signaling in cell development and highlights the significance of the bundle sheath in C3 photosynthesis.

Molecular Characterization of the Calvin Cycle Enzyme Phosphoribulokinase in the Stramenopile Alga Vaucheria litorea and the Plastid Hosting Mollusc Elysia chlorotica

Phosphoribulokinase （PRK）, a nuclear-encoded plastid-localized enzyme unique to the photosynthetic carbon reduction （Calvin） cycle, was cloned and characterized from the stramenopile alga Vaucheria litorea. This alga is the source of plastids for the mollusc （sea slug） Elysia chlorotica which enable the animal to survive for months solely by photoautotrophic CO2 fixation. The 1633-bp V. litorea prk gene was cloned and the coding region, found to be interrupted by four introns, encodes a 405-amino acid protein. This protein contains the typical bipartite target sequence expected of nuclearencoded proteins that are directed to complex （i.e. four membrane-bound） algal plastids. De novo synthesis of PRK and enzyme activity were detected in E. chlorotica in spite of having been starved of V. litorea for several months. Unlike the algal enzyme, PRK in the sea slug did not exhibit redox regulation. Two copies of partial PRK-encoding genes were isolated from both sea slug and aposymbiotic sea slug egg DNA using PCR. Each copy contains the nucleotide region spanning exon 1 and part of exon 2 of V litorea prk, including the bipartite targeting peptide. However, the larger prk fragment also includes intron 1. The exon and intron sequences of prk in E. chlorotica and V/itorea are nearly identical. These data suggest that PRK is differentially regulated in V. litorea and E. chlorotica and at least a portion of the V. litorea nuclear PRK gene is present in sea slugs that have been starved for several months.

FORMATION AND FEATURES OF CLOSE ASSOCIATION OF MITOCHONDRION-PLASTID

Study of nitrogen-fixation cell biology has gradually advanced to the study of only one kind of cells in root nodules, such as the infected cell, uninfected cell, cortex cell, from general structure of root nodules now. Some authors even start to study one kind of composition of the above-mentioned cells, for example, cell wall, cytoplasm, dictyosome, microbody and specially cytoplasmic inclusion, etc., because these studies can help us

Non-redundant Contribution of the Plastidial FAD8 ω-3 Desatumse to Glycerolipid Unsatumtion at Different Temperatures in Arabidopsis

Plastidial ω-3 desaturase FAD7 is a major contributor to trienoic fatty acid biosynthesis in the leaves of Arabidopsis plants. However, the precise contribution of the other plastidial ω-3 desaturase, FAD8, is poorly understood. Fatty acid and lipid analysis of several ω-3 desaturase mutants, including two insertion lines of AtFAD7 and AtFAD8, showed that FAD8 partially compensated the disruption of the AtFAD7 gene at 22℃, indicating that FAD8 was active at this growth temperature, contrasting to previous observations that circumscribed the FAD8 activity at low temperatures. Our data revealed that FAD8 had a higher selectivity for 18：2 acyl-lipid substrates and a higher preference for lipids other than galactolipids, particularly phosphatidylglycerol, at any of the temperatures studied. Differences in the mechanism controlling AtFAD7 and AtFAD8 gene expression at different temperatures were also detected. Confocal microscopy and biochemical analysis of FAD8-YFP over-expressing lines confirmed the chloroplast envelope localization of FAD8. Co-localization experiments suggested that FAD8 and FAD7 might be located in close vicinity in the envelope membrane. FAD8-YFP over-expressing lines showed a specific increase in 18：3 fatty acids at 22℃. Together, these results indicate that the function of both plastidial ω-3 desaturases is coordinated in a non-redundant manner.

Coordination of Plastid and Light Signaling Pathways upon Development of Arabidopsis Leaves under Various Photoperiods

Plants synchronize their cellular and physiological functions according to the photoperiod （the length of the light period） in the cycle of 24 h. Photoperiod adjusts several traits in the plant life cycle, including flowering and senes- cence in annuals and seasonal growth cessation in perennials. Photoperiodic development is controlled by the coordinated action of photoreceptors and the circadian clock. During the past 10 years, remarkable progress has been made in under- standing the molecular mechanism of the circadian clock, especially with regard to the transition of Arabidopsis from the vegetative growth to the reproductive phase. Besides flowering photoperiod also modifies plant photosynthetic struc- tures and traits. Light signals controlling biogenesis of chloroplasts and development of leaf photosynthetic structures are perceived both by photoreceptors and in chloroplasts. In this review, we provide evidence suggesting that the photope- riodic development of Arabidopsis leaves mimics the acclimation of plant to various light intensities. Furthermore, the chloroplast-to-nucleus retrograde signals that adjust acclimation to light intensity are proposed to contribute also to the signaling pathways that control photoperiodic acclimation of leaves.

OR^His, a Natural Variant of OR, Specifically Interacts with Plastid Division Factor ARC3 to Regulate Chromoplast Number and Carotenoid Accumulation

Chromoplasts are colored plastids that synthesize and store massive amounts of carotenoids.Chromoplast number and size define the sink strength for carotenoid accumulation in plants.However,nothing is known about the mechanisms controlling chromoplast number.Previously,a natural allele of Orange(OR),OR^His,was found to promote carotenoid accumulation by activating chromoplast differentiation and increasing carotenoid biosynthesis,but cells in orange tissues in melon fruit and cauliflower OR mutant have only one or two enlarged chromoplasts.In this study,we investigated an OR^His variant of Arabidopsis OR,genetically mimicking the melon OR^His allele,and found that it also constrains chromoplast number in Arabidopsis calli.Both in vitro and in vivo experiments demonstrate that OR^His specifically interacts with the Membrane Occupation and Recognition Nexus domain of ACCUMULATION AND REPLICATION OF CHLOROPLASTS 3(ARC3),a crucial regulator of chloroplast division.We further showed that OR^His interferes with the interaction between ARC3 and PARALOG OF ARC6(PARC6),another key regulator of chloroplast division,suggesting a role of OR^His in competing with PARC6 for binding to ARC3 to restrict chromoplast number.Overexpression or knockout of ARC3 in Arabidopsis OR^His plants significantly alters total carotenoid levels.Moreover,overexpression of the plastid division factor PLASTID DIVISION 1 greatly enhances carotenoid accumulation.These division factors likely alter carotenoid levels via their influence on chromoplast number and/or size.Taken together,our findings provide novel mechanistic insights into the machinery controlling chromoplast number and highlight a potential new strategy for enhancing carotenoid accumulation and nutritional value in food crops.

Cloning and Expression Pattern of a Gene Encoding a Putative Plastidic ATP/ADP Transporter from Helianthus tuberosus L.

Herein, we report the cloning and molecular characterization of a full cDNA encoding a putative plastidic ATP/ADP transporter, designated HtAATP, for Helianthus tuberosus L. The ATP/ADP translocator protein was isolated from the tuber-cDNA library of H. tuberosus for the first time. The predicted HtAATP protein was judged as a plastidic ATP/ADP translocator protein from its high homology at the amino acid sequence level to the two Arabidopsis thaliana plastidic ATP/ADP translocator proteins AATP1 and AATP2 （84.8% and 79.9% identity, respectively）. Amino acid sequence analysis of the primary structure of HtAATP revealed that it belonged to the plastidic ATP/ADP transporter family. Hydropathy prediction indicated that HtAATP gene product is a highly hydrophobic membrane protein that contains 10 transmembrane domains to form a spanning topology. Southern blotting analysis showed that the HtAATP gene is a single-copy gene in the H. tuberosus genome. Tissue distribution analysis showed that the HtAATP gene is prominently expressed in sink tissues. A stable expression pattern in tubers at different developmental stages implies an active involvement of HtAATP during carbohydrate formation.