Search

Abstract Background Mineral nutrients are one of the most basic components of plant tissue culture media. Nitrogen in the form of NH4+ and NO3- is the dominant mineral nutrient in most plant tissue culture formulations, with effects dependent on both the proportion and the amount of NH4+ and NO3-. The effects of nitrogen nutrition on the growth of nonembryogenic and embryogenic cell lines of sweet orange (C. sinensis (L.) Osbeck cv. 'Valencia'), tissues routinely used in citrus horticultural and plant improvement research, was explored using an experimental approach free of ion confounding that included a 2-component mixture (NH4+:K+) and a quantitative factor [NO3-] crossed by the mixture, thereby providing ion-specific estimates of proportional and amount effects. Results First, the linear mixture component, though only a comparison of the design space vertices, was highly significant for both tissue types and showed that NH4+ was required by both tissues. Second, the NH4+ * K+ mixture term was highly significant for both tissue types, revealing that NH4+ and K+ exhibit strong synergistic blending and showed that growth was substantially greater at certain blends of these two ions. Third, though the interaction between the NH4+:K+ mixture and NO3- amount on fresh weight accumulation for both tissue types was significant, it was substantially less than the main effect of the NH4+:K+ mixture. Fourth, a region of the design space was identified where fresh weight growth was increased 198% and 67% over the MS medium controls for nonembryogenic and embryogenic tissues. Conclusion By designing a mineral nutrient experiment free of ion confounding, a direct estimation of ion-specific proportional and amount effects on plant tissue growth is possible. When the ions themselves are the independent factors and/or mixture components, the resulting design space can be systematically explored to identify regions where the response(s) is substantially improved over current media formulations. In addition, because the response is over a defined experimental region, a specific medium formulation is more accurately interpreted as a coordinate in the specified design geometry.

We document high rates of triploidy in aspen (Populus tremuloides) across the western USA (up to 69% of genets), and ask whether the incidence of triploidy across the species range corresponds with latitude, glacial history (as has been documented in other species), climate, or regional variance in clone size. Using a combination of microsatellite genotyping, flow cytometry, and cytology, we demonstrate that triploidy is highest in unglaciated, drought-prone regions of North America, where the largest clone sizes have been reported for this species. While we cannot completely rule out a low incidence of undetected aneuploidy, tetraploidy or duplicated loci, our evidence suggests that these phenomena are unlikely to be significant contributors to our observed patterns. We suggest that the distribution of triploid aspen is due to a positive synergy between triploidy and ecological factors driving clonality. Although triploids are expected to have low fertility, they are hypothesized to be an evolutionary link to sexual tetraploidy. Thus, interactions between clonality and polyploidy may be a broadly important component of geographic speciation patterns in perennial plants. Further, cytotypes are expected to show physiological and structural differences which may influence susceptibility to ecological factors such as drought, and we suggest that cytotype may be a significant and previously overlooked factor in recent patterns of high aspen mortality in the southwestern portion of the species range. Finally, triploidy should be carefully considered as a source of variance in genomic and ecological studies of aspen, particularly in western U.S. landscapes. [ABSTRACT FROM AUTHOR]

Background: With the objective of combining multiple resistant traits from wild relative species in florist's chrysanthemums, trigeneric hybridization was conducted by crossing two intergeneric F1 hybrids Chrysanthemum grandiflorum x Artemisia vulgaris and Chrysanthemum crassum x Crossostephium chinense. Methodology/Principal Findings: To assess post-pollination phenomena, we investigated pollen germination on the stigma and embryo development, using fluorescence and scanning electron microscopy and paraffin-embedded sections, respectively. We selected eight putative trigeneric hybrid lines that showed the greatest morphological differences from the parents from among the progeny derived via embryo rescue. The hybridity of one trigeneric hybrid was further confirmed by fluorescent genomic in situ hybridization; in addition, the aphid resistance and salt tolerance of this hybrid were higher than those of the chrysanthemum parent and the C. grandiflorum x A. vulgaris F1 hybrid, respectively. Conclusions/Significance: The enhanced aphid resistance of the hybrid line reflects the inheritance of chromosomes from A. vulgaris, which carries genes that encode bioactive components. The enhanced salt tolerance of the trigeneric hybrid is attributable to inheritance of genetic materials from Chrysanthemum crassum and Crossostephium chinense, which act to maintain the compartmentation of Na+ and K+ ions and their selective transportation among different organs to avert deleterious effects and protect the photosynthetic apparatus. The results indicate that trigeneric hybridization between different bigeneric hybrids is a promising method for combination of multiple stress-resistance traits for improvement of chrysanthemum. [ABSTRACT FROM AUTHOR]

High resolution melting curve analysis (HRM) has been used as an efficient, accurate and cost-effective tool to detect single nucleotide polymorphisms (SNPs) or insertions or deletions (INDELs). However, its efficiency, accuracy and applicability to discriminate microsatellite polymorphism have not been extensively assessed. The traditional protocols used for SSR genotyping include PCR amplification of the DNA fragment and the separation of the fragments on electrophoresis-based platform. However, post-PCR handling processes are laborious and costly. Furthermore, SNPs present in the sequences flanking repeat motif cannot be detected by polyacrylamide-gel- electrophoresis based methods. In the present study, we compared the discriminating power of HRM with the traditional electrophoresis-based methods and provided a panel of primers for HRM genotyping in Citrus. The results showed that sixteen SSR markers produced distinct polymorphic melting curves among the Citrus spp investigated through HRM analysis. Among those, 10 showed more genotypes by HRM analysis than capillary electrophoresis owing to the presence of SNPs in the amplicons. For the SSR markers without SNPs present in the flanking region, HRM also gave distinct melting curves which detected same genotypes as were shown in capillary electrophoresis (CE) analysis. Moreover, HRM analysis allowed the discrimination of most of the 15 citrus genotypes and the resulting genetic distance analysis clustered them into three main branches. In conclusion, it has been approved that HRM is not only an efficient and cost- effective alternative of electrophoresis-based method for SSR markers, but also a method to uncover more polymorphisms contributed by SNPs present in SSRs. It was therefore suggested that the panel of SSR markers could be used in a variety of applications in the citrus biodiversity and breeding programs using HRM analysis. Furthermore, we speculate that the HRM analysis can be employed to analyse SSR markers in a wide range of applications in all other species. [ABSTRACT FROM AUTHOR]

The success of germination, growth and final yield of every crop depends to a large extent on the quality of the seeds used to grow the crop. Seed quality is defined as the viability and vigor attribute of a seed that enables the emergence and establishment of normal seedlings under a wide range of environments. We attempt to dissect the mechanisms involved in the acquisition of seed quality, through a combined approach of physiology and genetics. To achieve this goal we explored the genetic variation found in a RIL population of Solanum lycopersicum (cv. Moneymaker) x Solanum pimpinellifolium through extensive phenotyping of seed and seedling traits under both normal and nutrient stress conditions and root system architecture (RSA) traits under optimal conditions. We have identified 62 major QTLs on 21 different positions for seed, seedling and RSA traits in this population. We identified QTLs that were common across both conditions, as well as specific to stress conditions. Most of the QTLs identified for seedling traits co-located with seed size and seed weight QTLs and the positive alleles were mostly contributed by the S. lycopersicum parent. Co-location of QTLs for different traits might suggest that the same locus has pleiotropic effects on multiple traits due to a common mechanistic basis. We show that seed weight has a strong effect on seedling vigor and these results are of great importance for the isolation of the corresponding genes and elucidation of the underlying mechanisms. [ABSTRACT FROM AUTHOR]

Biological invasions can cause major ecological and economic impacts. During the early stages of invasions, eradication is desirable but tactics are lacking that are both effective and have minimal non-target effects. Mating disruption, which may meet these criteria, was initially chosen to respond to the incursion of light brown apple moth, Epiphyas postvittana (LBAM; Lepidoptera: Tortricidae), in California. The large size and limited accessibility of the infested area favored aerial application. Moth sex pheromone formulations for potential use in California or elsewhere were tested in a pine forest in New Zealand where LBAM is abundant. Formulations were applied by helicopter at a target rate of 40 g pheromone per ha. Trap catch before and after application was used to assess the efficacy and longevity of formulations, in comparison with plots treated with ground-applied pheromone dispensers and untreated control plots. Traps placed at different heights showed LBAM was abundant in the upper canopy of tall trees, which complicates control attempts. A wax formulation and polyethylene dispensers were most effective and provided trap shut-down near ground level for 10 weeks. Only the wax formulation was effective in the upper canopy. As the pheromone blend contained a behavioral antagonist for LBAM, 'false trail following' could be ruled out as a mechanism explaining trap shutdown. Therefore, 'sensory impairment' and 'masking of females' are the main modes of operation. Mating disruption enhances Allee effects which contribute to negative growth of small populations and, therefore, it is highly suitable for area-wide control and eradication of biological invaders. [ABSTRACT FROM AUTHOR]

Male sterile and seedless characters are highly desired for citrus cultivar improvement. In our breeding program, a male sterile cybrid pummelo, which could be considered as a variant of male fertile pummelo, was produced by protoplast fusion. Herein, ecotopic stamen primordia initiation and development were detected in this male sterile cybrid pummelo. Histological studies revealed that the cybrid showed reduced petal development in size and width, and retarded stamen primordia development. Additionally, disorganized cell proliferation was also detected in stamen-like structures (fused to petals and/or carpel). To gain new insight into the underlying mechanism, we compared, by RNA-Seq analysis, the nuclear gene expression profiles of floral buds of the cybrid with that of fertile pummelo. Gene expression profiles which identified a large number of differentially expressed genes (DEGs) between the two lines were captured at both petal primordia and stamen primordia distinguishable stages. For example, nuclear genes involved in nucleic acid binding and response to hormone synthesis and metabolism, genes required for floral bud identification and expressed in particular floral whorls. Furthermore, in accordance with flower morphology of the cybrid, expression of PISTILLATA (PI) was reduced in stamen-like structures, even though it was restricted to correct floral whorls. Down-regulated expression of APETALA3 (AP3) coincided with that of PI. These finding indicated that, due to their whorl specific effects in flower development, citrus class-B MADS- box genes likely constituted 'perfect targets' for CMS retrograde signaling, and that dysfunctional mitochondria seemed to cause male sterile phenotype in the cybrid pummelo. [ABSTRACT FROM AUTHOR]

The fundamental niche defined by five ions, NO3 -, PO4 3-, K+ , was mapped for Chlorella vulgaris (Trebouxiophyceae) and Peridinium cinctum (Dinophyceae) growth rates and maximum cell densities in batch cultures. A five dimensional ion-mixture experimental design was projected across a total ion concentration gradient of 1 to 30mM to delineate the ion-based, "potential" niche space, defined as the entire n-dimensional hypervolume demarcated by the feasible ranges of the independent factors under consideration. The growth rate-based, fundamental niche volumes overlapped for ca. 94% of the ion mixtures, although the regions of maximal growth rates and cell densities were different for each alga. Both C. vulgaris and P. cinctum exhibited similar positive responses to cations and negative responses to anions. It was determined that total ion concentration for these five ions, from 1 to 30 mM, did not directly affect either growth rate or maximal cell density for either alga, although it did play an interactive role with several ions. This study is the first that we are aware of to attempt the mapping of a multivariate, ion-based, fundamental niche volume. The implications of the experimental design utilized and the potential utility of this type of approach are discussed. [ABSTRACT FROM AUTHOR]+, and Cl- , was mapped for Chlorella vulgaris (Trebouxiophyceae) and Peridinium cinctum (Dinophyceae) growth rates and maximum cell densities in batch cultures. A five dimensional ion-mixture experimental design was projected across a total ion concentration gradient of 1 to 30mM to delineate the ion-based, "potential" niche space, defined as the entire n-dimensional hypervolume demarcated by the feasible ranges of the independent factors under consideration. The growth rate-based, fundamental niche volumes overlapped for ca. 94% of the ion mixtures, although the regions of maximal growth rates and cell densities were different for each alga. Both C. vulgaris and P. cinctum exhibited similar positive responses to cations and negative responses to anions. It was determined that total ion concentration for these five ions, from 1 to 30 mM, did not directly affect either growth rate or maximal cell density for either alga, although it did play an interactive role with several ions. This study is the first that we are aware of to attempt the mapping of a multivariate, ion-based, fundamental niche volume. The implications of the experimental design utilized and the potential utility of this type of approach are discussed. [ABSTRACT FROM AUTHOR]

Seven putative protease inhibitor (PPI) cDNAs, representing four protein families, were isolated from a grapefruit (Citrus paradisi Macf. Cv. Marsh) immature fruit flavedo cDNA library. Cloned open reading frames encoded proteins with similarity to, and protein signatures for: legume Kuntiz inhibitors (lkiL-1, lkiL-2, lkiL-3), potato trypsin inhibitor I (ptiIL-1), serpins (serpL-1), cystatins (cystL-1), and gamma thionins (gthL-1). Response of transcript abundance to fruit development and leaf wounding was determined for all but lkiL-1 using real-time RT-PCR. Immature leaves had the highest transcript levels for all PPIs. The gthL-1 transcript in immature leaves was the most abundant transcript but was absent from healthy mature leaves. In fruit flavedo, transcripts for all PPIs were most abundant in youngest fruit (<15 mm dia. fruit), and declined during development, but displayed different patterns of developmental change. Mechanical or Diaprepes root weevil (DRW) feeding damage to leaves caused a <10-fold reduction or had no effect on transcript level with the exception of gthL-1 which, as a result of damage, increased >50-fold in mature leaves and decreased >1400-fold in immature leaves. This developmental control of transcript response to wounding in a woody perennial is opposite of what has been observed for defensive proteinase inhibitors (PIs) in other plants (typically herbaceous and/or annual plants), where younger leaves typically invoke a higher defensive proteinase inhibitor transcript accumulation than older tissues. Except for gthL-1, the PPI transcripts were minimally responsive or unresponsive to wounding. Changes in PPI transcript levels suggest diverse roles for the products of these genes in citrus, with only gthL-1 responding in a defense-like manner. [Copyright &y& Elsevier]