High-Sensitivity Detection of Fruit Tree Viruses Using Bacterial Magnetic Particles

Prunus necrotic ring spot virus （PNRSV） and grapevine fanleaf virus （GFLV） were detected by fluoroimmunoassay using bacterial magnetic particles （BMPs）, and a double antibody sandwich enzyme linked immunosorbent assay （DAS-ELISA）. For the fluoroimmunoassay, fluorescein isothiocyanate labeled anti-PNRSV antibody or anti-GFLV antibody was conjugated onto BMPs of Magnetospirillum gryphiswaldense MSR-1. With this method, a very low minimum antigen concentration （1×10^6 dilution of the original sample concentration） could be detected. Using DAS-ELISA, the minimum antigen detection concentration was the original sample concentration. Thus, comparing these two methods, a BMP-based method could increase the sensitivity up to six orders of magnitude （10^6） higher than an ELISA-based method of detection PNRSV and GFLV.     

Growth-Defense Tradeoffs in Plants： A Balancing Act to Optimize Fitness

Growth-defense tradeoffs are thought to occur in plants due to resource restrictions, which demand prior- itization towards either growth or defense, depending on external and internal factors. These tradeoffs have profound implications in agriculture and natural ecosystems, as both processes are vital for plant survival, reproduction, and, ulti- mately, plant fitness. While many of the molecular mechanisms underlying growth and defense tradeoffs remain to be elucidated, hormone crosstalk has emerged as a major player in regulating tradeoffs needed to achieve a balance. In this review, we cover recent advances in understanding growth-defense tradeoffs in plants as well as what is known regard- ing the underlying molecular mechanisms. Specifically, we address evidence supporting the growth-defense tradeoff concept, as well as known interactions between defense signaling and growth signaling. Understanding the molecular basis of these tradeoffs in plants should provide a foundation for the development of breeding strategies that optimize the growth-defense balance to maximize crop yield to meet rising global food and biofuel demands.     

Arabinan Metabolism during Seed Development and Germination in Arabidopsis

Arabinans are found in the pectic network of many cell walls, where, along with galactan, they are present as side chains of Rhamnogalacturonan I. Whilst arabinans have been reported to be abundant polymers in the cell walls of seeds from a range of plant species, their proposed role as a storage reserve has not been thoroughly investigated. In the cell walls of Arabidopsis seeds, arabinose accounts for approximately 40% of the monosaccharide composition of non- cellulosic polysaccharides of embryos. Arabinose levels decline to -15% during seedling establishment, indicating that cell wall arabinans may be mobilized during germination. Immunolocalization of arabinan in embryos, seeds, and seedlings reveals that arabinans accumulate in developing and mature embryos, but disappear during germination and seedling establishment. Experiments using 14C-arabinose show that it is readily incorporated and metabolized in growing seedlings, indicating an active catabolic pathway for this sugar. We found that depleting arabinans in seeds using a fungal arabinanase causes delayed seedling growth, lending support to the hypothesis that these polymers may help fuel early seedling growth.     

Towards Characterization of the Chloroplast NAD（P）H Dehydrogenase Complex

The NAD（P）H dehydrogenase （NDH） complex in chloroplast thylakoid membranes functions in cyclic electron transfer, and in chlororespiration. NDH is composed of at least 15 subunits, including both chloroplast- and nuclear-encoded proteins. During the past few years, extensive proteomic and genetic research on the higher plant NDH complex has been carried out, resulting in identification of several novel nuclear-encoded subunits. In addition, a number of auxiliary proteins, which mainly regulate the expression of chloroplast-encoded ndh genes as well as the assembly and stabilization of the NDH complex, have been discovered and characterized. In the absence of detailed crystallographic data, the structure of the NDH complex has remained obscure, and therefore the role of several NDH-associated nuclear-encoded proteins either as auxiliary proteins or structural subunits remains uncertain. In this review, we summarize the current knowledge on the subunit composition and assembly process of the chloroplast NDH complex. In addition, a novel oligomeric structure of NDH, the PSI/NDH supercomplex, is discussed.     

Interaction between a Dark Septate Endophytic Isolate from Dendrobium sp. and Roots of D. nobile Seedlings

Interactions between an isolate of dark septate endophytes （DSE） and roots of Dendrobium nobile Lindl. seedlings are reported in this paper. The isolate was obtained from orchid mycorrhizas on Dendrobium sp. in subtropical forest. The fungus formed typical orchid mycorrhiza in aseptic co-culture with D. nobile seedlings on modified Murashige-Skoog （MMS） medium. Anatomic observations of the infected roots showed that the DSE hyphae invaded the velamen layer, passed through passage cells in exodermis, entered the cortex cells, and then formed fungal pelotons of orchid mycorrhiza. D. nobile seedlings＇ plant height, stem diameter, new roots number and biomass were greatly enhanced by inoculating the fungus to seedlings. The fungus was identified as Leptodontidium by sequencing the polymerase chain reaction-amplified rDNA ITS1-5,8S-ITS2 （internal transcribed spacer （ITS）） regions and comparison with similar taxa.     

Xyloglucans of Monocotyledons Have Diverse Structures

Except in the Poaceae, little is known about the structures of the xyloglucans in the primary walls of monocotyledons. Xyloglucan structures in a range of monocotyledon species were examined. Wall preparations were isolated, extracted with 6 M sodium hydroxide, and the extracts treated with a xyloglucan-specific endo-（1→4）-β-glucanase preparation. The oligosaccharides released were analyzed by high-performance anion-exchange chromatography and by matrix-assisted laser-desorption ionization time-of-flight mass spectrometry. Oligosaccharide profiles of the non-commelinid monocotyledons were similar to those of most eudicotyledons, indicating the xyloglucans were fucogalactoxyloglucans, with a XXXG a core motif and the fucosylated units XXFG and XLFG. An exception was Lemna minor （Araceae）, which yielded no fucosylated oligosaccharides and had both XXXG and XXGn core motifs. Except for the Arecales （palms） and the Dasypogonaceae, which had fucogalactoxyloglucans, the xyloglucans of the commelinid monocotyledons were structurally different. The Zingiberales and Commelinales had xyloglucans with both XXGn and XXXG core motifs; small proportions of XXFG units, but no XLFG units, were present. In the Poales, the Poaceae had xyloglucans with a XXGn core motif and no fucosylated units. In the other Poales families, some had both XXXG and XXGn core motifs, others had only XXXG; XXFG units were present, but XLFG units were not.     

In vitro selection of high-affinity DNA aptamers for streptavidin

In this study, we developed a systematic evolution of ligands by exponential enrichment （SELEX） method using a combination of magnetic beads immobilization and flow cytometric measurement. As an example, the selection of streptavidin-specific aptamers was performed. In this protocol, the conventional SELEX procedure was optimized, fiirst using magnetic beads for target immobilization to facilitate highly efficient separation of the binding single-stranded DNA （ssDNA） aptamers from the unbound ssDNAs, and second using flow cytometry and fluorescein labeling to monitor the enrichment. The sensitivity of flow cytometry was adequate for ssDNA quantification during the SELEX procedures. The streptavidin-specific aptamers obtained in this work can be used as tools for characterization of the occupancy of streptavidin-modified surfaces with biotinylated target molecules. The method described in the study is also generally applicable to target molecules other than streptavidin.     

A Comparative Analysis of Embryo and Endosperm Proteome from Seeds of Jatropha curcas

Jatropha curcas is an important economic plant for biodiesel, which is extracted mainly from the endosperm of its mature seeds. Despite the morphological and functional differences between the embryo and endosperm, proteomic characteristics of the two tissues are not yet known. Similar proteomic profiles were observed in the two-dimensional gel electrophoresis maps from the two tissues. There were 380 and 533 major protein spots in the embryo and endosperm, respectively. Fourteen identical spots, showing a notable change, were selected and identified by tandem mass spectrometry. Among these proteins, dihydrolipoamide acetyltransferase （spot 27） participates in tricarboxylic acid cycle, which is an amphibolic pathway. The two parts both included proteins related to stress （spots 8, 115, 118, 125, 130） and signal transduction （spots 7, 100, 108）. According to the volume percentage of proteins in embryo and endosperm, the proteins in endosperm （spots 54, 61, 73） were catabolism-related enzymes and reserves to provide the nutrition for seed germination; the proteins in embryo （spots 27, 62, 122） were inclined to anabolism and utilized the nutrition from the endosperm to generate a new life.     

Analyses of Sexual Reproductive Success in Transgenic and/or Mutant Plants

The pistil, the female reproductive organ of plants, is a key player in the success of sexual plant reproduction. Ultimately, the production of fruits and seeds depends on the proper pistil development and function. Therefore, the identification and characterization of pistil expressed genes is essential for a better understanding and manipulation of the plant reproduction process. For studying the function of pistil expressed genes, transgenic and/or mutant plants for the genes of interest are used. The present article provides a review of methods already exploited to analyze sexual reproductive success. We intend to supply useful information and to guide future experiments in the study of genes affecting pistil development and function.     

Quantitative Trait Loci for Panicle Layer Uniformity Identified in Doubled Haploid Lines of Rice in Two Environments

Uniformity of stem height in rice directly affects crop yield potential and appearance, and has become a vital index for rice improvement. In the present study, a doubled haploid （DH） population, derived from a cross between japonica rice Chunjiang 06 and indica rice TN1 was used to analyze the quantitative trait locus （QTL） for three related traits of paniclelayer-uniformity; that is, the tallest panicle height, the lowest panicle height and panicle layer disuniforrnity in two locations：Hangzhou （HZ） and Hainan （HN）. A total of 16 QTLs for three traits distributed on eight chromosomes were detected in two different environments. Two QTLs, qTPH-4 and qTPH-8 were co-located with the QTLs for qLPH-4 and qLPH-8, which were only significant in the HZ environment, whereas the qTPH-6 and qLPH-6 located at the same interval were only significant in the HN environment. Two QTLs, qPLD-10.1 and qPLD-10.2, were closely linked to qTPH-10, and they might have been at the same locus. One QTL, qPLD-3, was detected in both environments, explaining more than 23% of the phenotypic variations. The CJ06 allele of qPLD-3 could increase the panicle layer disuniformity by 9.23 and 4.74 cm in the HZ and HN environments. Except for qPLD-3, almost all other QTLs for the same trait were detected only in one environment, indicating that these three traits were dramatically affected by environmental factors. The results may be useful for elucidation of the molecular mechanism of panicle-layer-uniformity and marker assisted breeding for super-rice.     

Pathogenic mutations of nuclear genes associated with mitochondrial disorders

Mitochondrial disorders are clinical phenotypes associated with mitochondrial dysfunction, which can be caused by mutations in mitochondrial DNA （mtDNA） or nuclear genes. In this review, we summarized the pathogenic mutations of nuclear genes associated with mitochondrial disorders. These nuclear genes encode, components of mitochondrial translational machinery and structural subunits and assembly factors of the oxidative phosphorylation, that complex. The molecular mechanisms, that nuclear modifier genes modulate the phenotypic expression of mtDNA mutations, are discussed in detail.     

Expression of the Arabidopsis thaliana Histone Gene AtHTA1 Enhances Rice Transformation Efficiency

We expressed the Arabidopsis thaliana histone AtHTA1 in rice under the control of the maize ubiquitin promoter. Transformation efficiencies of rice plants that constitutively expressed AtHTA 1 were 28-44% higher than calli containing an empty vector control. Furthermore, co-infection of rice calli with a vector containing AtHTA 1 and another vector with the target gene increased transformation by 27-50%. Thus, expression of AtHTA 1 either transiently or in stably transformed cells improved rice transformation efficiency.     

Arabidopsis STAY-GREEN2 Is a Negative Regulator of Chlorophyll Degradation during Leaf Senescence

Chlorophyll （Chl） degradation causes leaf yellowing during senescence or under stress conditions. For Chl breakdown, STAY-GREEN1 （SGR1） interacts with Chl catabolic enzymes （CCEs） and light-harvesting complex II （LHCII） at the thylakoid membrane, possibly to allow metabolic channeling of potentially phototoxic Chl breakdown intermediates. Among these Chl catabolic components, SGR1 acts as a key regulator of leaf yellowing. In addition to SGR1 （At4g22920）, the Arabidopsis thaliana genome contains an additional homolog, SGR2 （At4g11910）, whose biological function remains elusive. Under senescence-inducing conditions, SGR2 expression is highly up-regulated, similarly to SGR1 expression. Here we show that SGR2 function counteracts SGR1 activity in leaf Chl degradation; SGR2-overexpressing plants stayed green and the sgr2-1 knockout mutant exhibited early leaf yellowing under age-, dark-, and stress-induced senescence conditions. Like SGR1, SGR2 interacted with LHCII but, in contrast to SGR1, SGR2 interactions with CCEs were very limited. Furthermore, SGR1 and SGR2 formed homo- or heterodimers, strongly suggesting a role for SGR2 in negatively regulat- ing Chl degradation by possibly interfering with the proposed CCE-recruiting function of SGR1. Our data indicate an antagonistic evolution of the functions of SGR1 and SGR2 in Arabidopsis to balance Chl catabolism in chloroplasts with the dismantling and remobilizing of other cellular components in senescing leaf cells.     

Conserved Functions of Arabidopsis and Rice CC-Type Glutaredoxins in Flower Development and Pathogen Response

Glutaredoxins （GRXs） are ubiquitous oxidoreductases that play a crucial role in response to oxidative stress by reducing disulfides in various organisms. In planta, three different GRX classes have been identified according to their active site motifs. CPYC and CGFS classes are found in all organisms, whereas the CC-type class is specific for higher land plants. Recently, two Arabidopsis CC-type GRXs, ROXY1 and ROXY2, were shown to exert crucial functions in petal and anther initiation and differentiation. To analyze the function of CC-type GRXs in the distantly related monocots, we isolated and characterized OsROXY1 and OsROXY2-two rice homologs of ROXY1. Both genes are expressed in vegetative and reproductive stages. Although rice flower morphology is distinct from eudicots, OsROXY1/2 floral expression patterns are similar to their Arabidopsis counterparts ROXY1/2. Complementation experiments demonstrate that OsROXY1 and OsROXY2 can fully rescue the roxyl floral mutant phenotype. Overexpression of OsROXY1, OsROXY2, and ROXY1 in Arabidopsis causes similar vegetative and reproductive plant developmental defects. ROXY1 and its rice homologs thus exert a conserved function during eudicot and monocot flower development. Strikingly, overexpression of these CC-type GRXs also leads to an increased accumulation of hydrogen peroxide levels and hyper-susceptibility to infection from the necrotrophic pathogen Botrytis cinerea, revealing the importance of balanced redox processes in flower organ develop- ment and pathogen defence.