Unique Chloroplast Research Articles

Mapping of subcellular local pH in the marine diatom Phaeodactylum tricornutum.

Diatoms are one of the most important phytoplankton on Earth. They comprise at least ten thousand species and contribute to up to 20% of the global primary production. Because of serial endosymbiotic events and horizontal gene transfers, diatoms have developed a "secondary plastid" bounded by four membranes containing a large phase-separated compartment, termed the pyrenoid. However, the physiological significance of this unique chloroplast morphology is poorly understood. Characterization of fundamental physiological parameters such as local pH in various subcellular compartments should facilitate a greater understanding of the physiological roles of the unique structure of the secondary plastid. A promising method to estimate local pH is the in situ expression of the pH-sensitive green fluorescent protein. Here, we first developed the molecular tool for the mapping of in situ local pH in the diatom Phaeodactylum tricornutum by heterologously expressing pHluorin2 in the cytosol, periplastidal compartment (PPC; the space in between two sets of outer and inner chloroplast envelopes), chloroplast stroma, and the pyrenoid matrix. Our data suggested that PPC and the pyrenoid matrix are more acidic than the adjacent areas, the cytosol and the chloroplast stroma. Finally, absolute pH values at each compartment were estimated from the ratiometric fluorescence of a recombinant pHluorin2 protein, giving pH values of approximately 7.9, 6.8, 8.0, and 7.5 respectively, for the cytosol, PPC, stroma, and pyrenoid of the P. tricornutum cells, indicating the occurrence of pH gradients and the associated electrochemical potentials at their boundary.

Tallapoosa Cane (Arundinaria alabamensis), a new species of temperate bamboo (Poaceae: Bambusoideae) from East Central Alabama

Arundinaria alabamensis (Tallapoosa Cane) is described as a new species of North American temperate woody bamboo. Recognition of this species is consistent with molecular genetic data that suggests an origin through hybridization and subsequent diversification, as it bears a unique chloroplast DNA haplotype most similar to A. gigantea (River Cane), nuclear DNA haplotypes that cluster with A. appalachiana (Hill Cane) and A. tecta (Switch Cane), and a distinct AFLP fingerprint. Tallapoosa Cane can be distinguished from the other North American Arundinaria by a combination of vegetative characters including larger leaf size, foliage sheath pubescence, and a distinctive branch complement. This Alabama endemic is currently known from eight populations across four counties: Cleburne (3), Lee (3), Macon (1), and Randolph (1). The new species is described and compared with the related species of Arundinaria, and an identification key is included along with a comparative table based on morphological characters.

Reassessment of Annamocarya sinesis (Carya sinensis) Taxonomy through Concatenation and Coalescence Phylogenetic Analysis.

Due to its peculiar morphological characteristics, there is dispute as to whether the genus of Annamocarya sinensis, a species of Juglandaceae, is Annamocarya or Carya. Most morphologists believe it should be distinguished from the Carya genus while genomicists suggest that A. sinensis belongs to the Carya genus. To explore the taxonomic status of A. sinensis using chloroplast genes, we collected chloroplast genomes of 16 plant species and assembled chloroplast genomes of 10 unpublished Carya species. We analyzed all 26 species’ chloroplast genomes through two analytical approaches (concatenation and coalescence), using the entire and unique chloroplast coding sequence (CDS) and entire and protein sequences. Our results indicate that the analysis of the CDS and protein sequences or unique CDS and unique protein sequence of chloroplast genomes shows that A. sinensis indeed belongs to the Carya genus. In addition, our analysis shows that, compared to single chloroplast genes, the phylogeny trees constructed using numerous genes showed higher consistency. Moreover, the phylogenetic analysis calculated with the coalescence method and unique gene sequences was more robust than that done with the concatenation method, particularly for analyzing phylogenetically controversial species. Through the analysis, our results concluded that A. sinensis should be called C. sinensis.

The complete plastid genome of Selaginella erythropus (Selaginellaceae), a species with distinctive giant chloroplasts

The plastid genome of the deep-shade plant Selaginella erythropus, which has highly unusual chloroplasts, was characterized using Illumina pair-end sequencing. This plastome is 140,151 bp in length with a large single-copy region (LSC) of 56,133 bp, a small single-copy region (SSC) of 61,268 bp, and two direct repeats (DRs) of 11,375 bp. The overall GC content is 50.68%, while those of LSC, SSC, and DR are 48.96%, 50.3%, and 55.96%, respectively. The plastome contains 102 genes, including 76 protein-coding, 15 tRNA (12 tRNA species), and 8 rRNA genes (4 rRNA species). The phylogenetic analysis shows that S. erythropus is closely related to S. moellendorffii and S. doederleinii. This result is consistent with the previous phylogenetic relationship inferred from multiple plastid and nuclear loci. However, only S. erythropus has the two-zoned giant chloroplast, the bizonoplast. The plastome provides an excellent reference for understanding the unique chloroplast differentiation in Selaginellaceae.

Population Demographic History of a Rare and Endangered Tree Magnolia sprengeri Pamp. in East Asia Revealed by Molecular Data and Ecological Niche Analysis

Quaternary climate and environment oscillations have profoundly shaped the population dynamic history and geographic distributions of current plants. However, how the endangered and rare tree species respond to the climatic and environmental fluctuations in the subtropical regions of China in East Asia still needs elucidation. In this study, we collected 36 natural populations of an endangered and rare tree species Magnolia sprengeri Pamp. in subtropical China to determine the demographic history, and modeled the changes of geographic distributions of this species in East Asia based on the MaxEnt ecological niche analyses. In addition, we sequenced three maternally inherited chloroplast DNA fragments (matK, trnH-psbA, and rbcL) for all the natural populations which covered the whole geographic distributions of M. sprengeri. Population genetic analysis showed that the endangered tree species have a low level of chloroplast DNA diversity. However, the genetic variation contribution within populations was greater than that among populations (FST = 0.276), which demonstrated a high level of genetic differentiation. Interestingly, some unique chloroplast DNA haplotypes and higher genetic variations were identified in the Qinling-Daba Mountains, Central China, and Tianmu Mountains of Zhejiang province, East of China in East Asia. Combining with the species distribution modeling, we speculated that these areas might be the potential glacial refugia for the endangered plant M. sprengeri. Phylogeographic analysis demonstrated that the geographic factors (e.g., mountains, rivers, and other isolation barriers) had little effect on the genetic divergence among populations. Ecological niche modeling further revealed that the natural populations of M. sprengeri did not experience significant geographic distribution changes from the last glacial maximum to the present time. These findings are in line with the analysis results of the multimodal mismatch patterns of the chloroplast DNA variations. To protect the endangered species M. sprengeri, in situ and ex situ conservation strategies should be formulated for the natural populations with higher genetic variations.

The palaeoendemic conifer Pherosphaera hookeriana (Podocarpaceae) exhibits high genetic diversity despite Quaternary range contraction and post glacial bottlenecking

Glacial relict plants are often endangered because extant populations can be small, geographically isolated and persist in suboptimal environments, leading to increased clonality and reduced genetic diversity putting their survival at further risk. This study examines how restriction to interglacial refugia has impacted the genetic diversity and structure of the threatened Tasmanian palaeoendemic, Pherosphaera hookeriana W. Archer bis. This species is a poorly dispersed, dioecious conifer that, having once been a major component of Last Glacial vegetation, is now limited to 30 known populations. Genetic diversity and structure were assessed using fifteen nuclear and nine chloroplast SSRs in 23 populations representing the species’ entire range. Changes in distribution and abundance from the Last Glacial to present were investigated by examining the fossil record, approximate Bayesian computation (ABC) and species distribution modelling. Despite fossil and ABC based evidence for a postglacial bottleneck, species-level genetic diversity (He = 0.56 and Ne = 2.86) exceeded that of some conifers with far wider distributions. Significant genetic structure (Fst = 0.127, Jost’s D = 0.203) was present, with most populations dominated by distinct nuclear SSR genetic clusters and having unique chloroplast haplotypes. Unexpectedly, clonality plays only a small role in population level regeneration. Genetic diversity has likely been maintained due to dioecy, persistence in multiple parts of its range and extant populations being directly descended from proximate glacial populations. Protecting populations from the mounting threat of fire will remain crucial for the in situ conservation of P. hookeriana.

Length variation of chloroplast simple sequence repeats in the genus Eucalyptus L'Hér.

Eucalyptus L'Hér. is an economically important genus of plants with several environmental significances and great industrial advantages. To accelerate breeding and conservation studies, efforts on molecular breeding and molecular genetic analysis are underway in the genus Eucalyptus. Despite these efforts, no sufficient information is available about common, polymorphic and unique chloroplast simple sequence repeats (cpSSRs) in the genus Eucalyptus. . These repeats consist of 1-6 nucleotides and play important role in the development of molecular markers, genetic mapping and plant breeding. In the present study, a total of 920 cpSSRs were detected and length variation of cpSSRs analysed between each pair of species among 31 chloroplast genome sequences of the genus Eucalyptus. Additionally, cross species transferability of common and polymorphic cpSSRs were also observed. The common, unique and putative polymorphic cpSSRs analysed in this study can be used for species identification and genetic diversity studies of Eucalyptus.

Selective Activation of Chloroplast psbD Light-Responsive Promoter and psaA/B Promoter in Transplastomic Tobacco Plants Overexpressing Arabidopsis Sigma Factor AtSIG5.

Plastid-encoded eubacterial-type RNA polymerase (PEP) plays a critical role in the transcription of photosynthesis genes in chloroplasts. Notably, some of the reaction center genes, including psaA, psaB, psbA, and psbD genes, are differentially transcribed by PEP in mature chloroplasts. However, the molecular mechanism of promoter selection in the reaction center gene transcription by PEP is not well understood. Sigma factor proteins direct promoter selection by a core PEP in chloroplasts as well as bacteria. AtSIG5 is a unique chloroplast sigma factor essential for psbD light-responsive promoter (psbD LRP) activity. To analyze the role of AtSIG5 in chloroplast transcription in more detail, we assessed the effect of AtSIG5 hyper-expression on the transcription of plastid-encoded genes in chloroplast transgenic plants. The chloroplast transgenic tobacco (CpOX-AtSIG5) accumulates AtSIG5 protein at extremely high levels in chloroplasts. Due to the extremely high-level expression of recombinant AtSIG5, most PEP holoenzymes are most likely to include the recombinant AtSIG5 in the CpOXAtSIG5 chloroplasts. Thus, we can assess the promoter preference of AtSIG5 in vivo. The overexpression of AtSIG5 significantly increased the expression of psbD LRP transcripts encoding PSII reaction center D2 protein and psaA/B operon transcripts encoding PSI core proteins. Furthermore, run-on transcription analyses revealed that AtSIG5 preferentially recognizes the psaA/B promoter, as well as the psbD LRP. Moreover, we found that psbD LRP is constitutively active in CpOX-AtSIG5 plants irrespective of light and dark. AtSIG5 probably plays a significant role in differential transcription of reaction center genes in mature chloroplasts.

The chloroplast proteome response to drought stress in cassava leaves

Cassava is an important tropical crop with strong resistance to drought stress. The chloroplast, the site of photosynthesis, is sensitive to stress, and the drought-response proteins in cassava chloroplasts are worthy of investigation. In this study, cassava leaves were collected for ultra-structure observation from plants subjected to different drought stress conditions. Our results showed that drought stress can promote starch accumulation in cassava chloroplasts. To evaluate changes in chloroplast proteins under different drought conditions, two-dimensional electrophoresis was performed using purified chloroplasts, which resulted in the identification of 26 unique chloroplast proteins responsive to drought stress. These drought-responsive proteins are predominantly related to photosynthesis, carbon and nitrogen metabolism, and amino acid metabolism. Among them, most photosynthesis-related proteins are downregulated, with decreases in photosynthetic parameters upon drought stress. Several proteins associated with carbon and nitrogen metabolism, including rubisco and carbonic anhydrase, were upregulated, which might promote drought tolerance in cassava by enhancing the carbohydrate conversion efficiency and protecting the plant from oxidative stress. Our proteomic data not only provide insight into the complement of proteins in cassava chloroplasts but also further our overall understanding of drought-responsive proteins in cassava chloroplasts.

N-degron specificity of chloroplast ClpS1 in plants.

The prokaryotic N-degron pathway depends on the Clp chaperone-protease system and the ClpS adaptor for recognition of N-degron bearing substrates. Plant chloroplasts contain a diversified Clp protease, including the ClpS homolog ClpS1. Several candidate ClpS1 substrates have been identified, but the N-degron specificity is unclear. Here, we employed invitro ClpS1 affinity assays using eight N-degron green fluorescence protein reporters containing either F, Y, L, W, I, or R in the N-terminal position. This demonstrated that ClpS1 has a restricted N-degron specificity, recognizing proteins bearing an N-terminal F or W, only weakly recognizing L, but not recognizing Y or I. This affinity is dependent on two conserved residues in the ClpS1 binding pocket and is sensitive to FR dipeptide competition, suggesting a unique chloroplast N-degron pathway.

Algal Sources of Sequestered Chloroplasts in the Sacoglossan Sea Slug Elysia crispata Vary by Location and Ecotype

Sacoglossan sea slugs feed by suctorially consuming siphonaceous green algae. Most sacoglossan species are feeding specialists, but the Caribbean coral reef-dwelling Elysia crispata is polyphagous and sequesters chloroplasts from multiple algal species into cells lining its digestive diverticulum for use in photosynthesis. We have used sequences of the chloroplast-encoded rbcL gene to compare the chloroplast donor algae in five populations of E. crispata from various Caribbean locations. We found that E. crispata utilizes more algal species than was previously known, including some algae previously not reported as present in the region. In addition, slugs from each location had unique chloroplast arrays with little overlap, except that all locations had slugs feeding on algae within the genus Bryopsis. This variation in diet between locations suggests that the slugs may be exhibiting local adaptation in their dietary choices, and it highlights ecological differences between the Caribbean-wide reef-dwelling ecotypes and the mangrove lagoon ecotypes found in the Florida Keys.

Pleistocene divergence of two disjunct conifers in the eastern Australian temperate zone

The eastern Australian temperate biota harbours many plants with fragmented geographic ranges distributed over 1000s of kilometres, yet the spatial genetic structure of their populations remains largely unstudied. In this study, we investigated genetic variation of the nuclear internal transcribed spacer (ITS) and chloroplast DNA sequences to disentangle the phylogeography of two widely distributed but highly fragmented eastern Australian fire-sensitive temperate conifers: Callitris oblonga (12 populations and 121 individuals) and C. rhomboidea (22 populations and 263 individuals). The three highly disjunct populations of C. oblonga all had unique chloroplast and ITS haplotypes consistent with the classification of these three populations as distinct subspecies. Molecular dating indicates that divergences of these populations occurred pre- to mid- Pleistocene (2.66 to 1.08 mya). Callitris rhomboidea showed greater diversity of chloroplast haplotypes which was strongly phylogeographically structured (Gst = 0.972), with haplotypes unique to specific geographic regions. ITS haplotype diversity was far higher than in C. oblonga with 38 haplotypes displaying high geographic structuring (Gst = 0.387) with many population-specific haplotypes. A phylogeographic break was identified between populations north and south of eastern Victoria dated at 0.43–0.47 mya. In both species, the strong genetic structuring of both chloroplast and ITS haplotypes provides evidence that their widespread ranges have resulted from long term persistence in low fire frequency refugia combined with poor dispersal. Any loss of populations due to increasing fire frequency or habitat loss is likely to result in a reduction of genetic diversity.

Evidence for both long-distance dispersal and isolation in the Southern Oceans: molecular phylogeny of Sophora sect Edwardsia (Fabaceae)

ABSTRACTWe examined the phylogenetic relationships within Sophora sect. Edwardsia using DNA sequences from the chloroplast trnQ-5′rps16 and trnHGUG-psbA intergenic spacers and the nuclear-encoded chloroplast-expressed glutamine synthetase gene. Sequences were analysed with median-joining networks and phylogenetic approaches. Low sequence diversity was detected, which is consistent with past genetic studies of the section. Chloroplast and nuclear sequences are shared across large geographic distances. The New Zealand species did not form a monophyletic group, nor did the species from Chile. However, species on some Pacific Islands (Lord Howe Island, Easter Island, Hawaii and French Polynesia) and Réunion Island in the Indian Ocean appear to have unique chloroplast haplotypes, indicating isolation. The S. chrysophylla chloroplast haplotype derives from the French Polynesian haplotype rather than S. denudata from Réunion Island, with which it shares morphological characters. In the nuclear phylogeny Sophora macrocarpa was sister to the remaining species that were sequenced in the section, a relationship that has been previously suggested from morphological analysis.

Population Dynamics Among six Major Groups of the Oryza rufipogon Species Complex, Wild Relative of Cultivated Asian Rice.

BackgroundUnderstanding population structure of the wild progenitor of Asian cultivated rice (O. sativa), the Oryza rufipogon species complex (ORSC), is of interest to plant breeders and contributes to our understanding of rice domestication. A collection of 286 diverse ORSC accessions was evaluated for nuclear variation using genotyping-by-sequencing (113,739 SNPs) and for chloroplast variation using Sanger sequencing (25 polymorphic sites).ResultsSix wild subpopulations were identified, with 25 % of accessions classified as admixed. Three of the wild groups were genetically and geographically closely related to the O. sativa subpopulations, indica, aus and japonica, and carried O. sativa introgressions; the other three wild groups were genetically divergent, had unique chloroplast haplotypes, and were located at the geographical extremes of the species range. The genetic subpopulations were significantly correlated (r 2 = 0.562) with traditional species designations, O. rufipogon (perennial) and O. nivara (annual), differentiated based on morphology and life history. A wild diversity panel of 95 purified (inbred) accessions was developed for future genetic studies.ConclusionsOur results suggest that the cultivated aus subpopulation is most closely related to an annual wild relative, japonica to a perennial wild relative, and indica to an admixed population of diverse annual and perennial wild ancestors. Gene flow between ORSC and O. sativa is common in regions where rice is cultivated, threatening the identity and diversity of wild ORSC populations. The three geographically isolated ORSC populations harbor variation rarely seen in cultivated rice and provide a unique window into the genetic composition of ancient rice subpopulations.Electronic supplementary materialThe online version of this article (doi:10.1186/s12284-016-0119-0) contains supplementary material, which is available to authorized users.

Genetic and Physical Interaction Studies Reveal Functional Similarities between ALBINO3 and ALBINO4 in Arabidopsis.

ALBINO3 (ALB3) is a well-known component of a thylakoid protein-targeting complex that interacts with the chloroplast signal recognition particle (cpSRP) and the cpSRP receptor, chloroplast filamentous temperature-sensitive Y (cpFtsY). Its protein-inserting function has been established mainly for light-harvesting complex proteins, which first interact with the unique chloroplast cpSRP43 component and then are delivered to the ALB3 integrase by a GTP-dependent cpSRP-cpFtsY interaction. In Arabidopsis (Arabidopsis thaliana), a subsequently discovered ALB3 homolog, ALB4, has been proposed to be involved not in light-harvesting complex protein targeting, but instead in the stabilization of the ATP synthase complex. Here, however, we show that ALB3 and ALB4 share significant functional overlap, and that both proteins are required for the efficient insertion of cytochrome f and potentially other subunits of pigment-bearing protein complexes. Genetic and physical interactions between ALB4 and ALB3, and physical interactions between ALB4 and cpSRP, suggest that the two ALB proteins may engage similar sets of interactors for their specific functions. We propose that ALB4 optimizes the insertion of thylakoid proteins by participating in the ALB3-cpSRP pathway for certain substrates (e.g. cytochrome f and the Rieske protein). Although ALB4 has clearly diverged from ALB3 in relation to the partner-recruiting C-terminal domain, our analysis suggests that one putative cpSRP-binding motif has not been entirely lost.

Chloroplast diversity indicates two independent maternal lineages in cultivated grapevine (Vitis vinifera L. subsp. vinifera)

Chloroplast markers are powerful tools for research into relationships among grapevine (Vitis vinifera L. subsp. vinifera) cultivars. However, the high number of regions common to the chloroplast and mitochondrion genomes described in grapevine could interfere with correct phylogeny reconstruction. In this study, we established a unique chloroplast marker (UCM) set and investigated the chloroplast haplotype diversity of 17 grapevine cultivars and seven Asian Vitis species. Sequencing of four UCMs revealed four haplotype groups in grapevine based on three nucleotide substitutions, three simple sequence repeats, and one 54 nucleotide (nt) deletion in the trnC-petN region. The constructed molecular-variance parsimony and statistical parsimony networks indicated that two independent maternal lineages of grapevine cultivars originated from a core group of Asian Vitis species. The presence and absence of a newly discovered 54 nt deletion corresponded to the two maternal lineages: deletion (D) and non-deletion (ND) lineages. The D lineage consisted of three haplotypes, represented by ‘Furmint’, ‘Gouais blanc’, and ‘Sauvignon blanc’. Ancient noble cultivars, such as ‘Pinot noir’, ‘Riesling’, and ‘Afus ali’, belong to a single haplotype group (ND) in which the deletion was absent. Our results provide compelling evidence for the dual maternal origin of grapevine, and suggest the occurrence of an ancient hybridization event.

Genetic Interactions Reveal that Specific Defects of Chloroplast Translation are Associated with the Suppression of var2‐Mediated Leaf Variegation

Arabidopsis thaliana L. yellow variegated (var2) mutant is defective in a chloroplast FtsH family metalloprotease, AtFtsH2/VAR2, and displays an intriguing green and white leaf variegation. This unique var2-mediated leaf variegation offers a simple yet powerful tool for dissecting the genetic regulation of chloroplast development. Here, we report the isolation and characterization of a new var2 suppressor gene, SUPPRESSOR OF VARIEGATION8 (SVR8), which encodes a putative chloroplast ribosomal large subunit protein, L24. Mutations in SVR8 suppress var2 leaf variegation at ambient temperature and partially suppress the cold-induced chlorosis phenotype of var2. Loss of SVR8 causes unique chloroplast rRNA processing defects, particularly the 23S-4.5S dicistronic precursor. The recovery of the major abnormal processing site in svr8 23S-4.5S precursor indicate that it does not lie in the same position where SVR8/L24 binds on the ribosome. Surprisingly, we found that the loss of a chloroplast ribosomal small subunit protein, S21, results in aberrant chloroplast rRNA processing but not suppression of var2 variegation. These findings suggest that the disruption of specific aspects of chloroplast translation, rather than a general impairment in chloroplast translation, suppress var2 variegation and the existence of complex genetic interactions in chloroplast development.

Morphological and genetic variation within and among four Quercus petraea and Q. robur natural populations

Numeric-taxonomical and molecular techniques [nuclear simple sequence repeats (nSSRs), expressed sequence tag (EST) SSRs, and chloroplast SSRs] were used to estimate morphological and genetic differentiation within and among 4 Quercus petraea and Q. robur natural populations in Turkey. Canonical discriminant analysis (CDA) and principal component analysis (PCA) showed that 3 out of 15 studied leaf morphological characters (clustered hairs, number of intercalary veins, petiole length) mainly accounted for the discrimination between species. In accordance with earlier observations, the mean genetic differentiation between Q. petraea and Q. robur at 8 microsatellite loci (F_{ST} = 0.030) and at chloroplast microsatellites (G_{ST} = 0.22) was low, potentially as the result of interspecific gene flow or shared ancestral polymorphisms. Chloroplast microsatellite analyses showed unique chloroplast haplotypes in Turkey, suggesting a glacial refuge in this region. Nuclear microsatellite ssrQrZAG96, described in other studies as being potentially under directional selection (outlier locus) due to high interspecific differentiation, showed considerably lower differentiation between species in the present study (F_{ST} = 0.028). These different patterns of genetic variation suggest different local adaptations of the species in this putative glacial refugial area in Turkey. It may also be that this marker is not directly associated with morphological or adaptive species differences. Interestingly, the analysed Q. petraea and Q. robur populations appear to have ecological requirements with regard to water availability that are different than those described for European populations. The analysis of additional populations within the species distribution range in Turkey is necessary to confirm this pattern.

Origins of white (Corchorus capsularis L.) and dark (C. olitorius L.) jute: a reevaluation based on nuclear and chloroplast microsatellites

Using a suite of morphological traits and neutral molecular markers, we have reevaluated the origins of the two cultivated jute species. The nine Corchorus species, which are restricted to both Africa and Asia, were phenotyped for bast fibre yield- and quality-linked traits, morpho-phenetically classified based on those traits’ similarities, genotyped by nuclear microsatellites and haplotyped by chloroplast microsatellites. The two cultivated jute species contain ~70% of the neutral genetic diversity present in their wild relatives. Phylogenetic analyses using 38 highly polymorphic nuclear microsatellites identified C. aestuans as the common ancestor to both the cultivated jute species. C. urticifolius is the nuclear progenitor of C. olitorius (dark jute), but no close nuclear progenitor of C. capsularis (white jute) could be identified. Although either C. aestuans or C. pseudo-olitorius or both appear to be the possible cytoplasmic progenitors of white jute, the matrilineal ancestry of dark jute remains obscure. However, the presence of a single, unique chloroplast haplotype in each of the two cultivated species indicates the involvement of other unknown wild relatives. Taken together with archaeobotanical evidence, our results suggest that dark jute had its origin in equatorial region of east Africa, but was domesticated in India. We could not support an Indo-Myanmar origin of white jute, and possibly it also originated in Africa, but was domesticated in Asia.

The cpSRP54‐cpFtsY Interaction in the Chloroplast SRP Pathway

The universally conserved signal recognition particle (SRP) and SRP receptor (SR) mediate the cotranslational targeting of proteins to cellular membranes. In contrast, a recently discovered unique chloroplast SRP in green plants is primarily dedicated to the post‐translational targeting of light harvesting chlorophyll a/b binding (LHC) proteins to the thylakoid membranes. The pathway involves cpSRP54 and its receptor cpFtsY, two GTPases that are similar to the cytosolic SRP54 and SR GTPases. Intriguingly, the otherwise universally conserved SRP RNA which accelerates complex formation between the two GTPases has not been found in the chloroplast pathway. Instead, a new 43‐kDa protein, cpSRP43, forms the chloroplast SRP together with cpSRP54. Kinetic analyses have shown that cpSRP43 does not significantly affect the rate of the cpSRP54·cpFtsY complex formation or the GTP hydrolysis rate of the complex. Instead, cpSRP43 facilitates the substrate recognition through interactions with the cargo proteins, LHCPs. This project seeks to understand how cpSRP54 and cpFtsY are able to associate more efficiently than their bacterial homologues in the absence of the SRP RNA by studying their complex structure using crystallography and lysine footprinting mass spectrometry. To date, 2‐dimensional crystal plates have been obtained, and progress continues toward the determination of a cpSRP54·cpFtsY structure.