Search

Abstract Constitutive overexpression of phosphate (Pi) transporter family 1 often results in the accumulation of toxic levels of Pi, which causes growth retardation in plants. In contrast, we had previously reported that root epidermis-specific overexpression of the phosphate transporter TaPT2 in Arabidopsis leads to improved growth and Pi use efficiency. In the present study, we used promoters AtHKT1;1 and SKOR, which are predominantly expressed in the vascular bundle tissues, to overexpress TaPT2. Transgenic lines exhibited increased shoot growth compared to wild type plants under normal- and low-Pi conditions, along with elevated root Pi and total P content, and higher xylem sap Pi concentration, specifically under low-Pi conditions. This was attributed to moderate Pi accumulation in the xylem parenchyma cells, enhancing the Pi uploading capacity to the xylem. SKOR-TaPT2, however, did not complement pho1 mutant, which was defective in uploading Pi to the xylem. The transcriptional levels of VPT1 and VPT3, which are responsible for transporting excess Pi into a vacuole, were upregulated in SKOR promoter lines under normal-Pi conditions. Our results suggested that root vascular bundle-specific expression of TaPT2 is another promising strategy for increasing biomass production, Pi uptake, and Pi use efficiency while preventing growth retardation in transgenic plants.

Abstract Background Increasing rice demand is one of the consequences of the steadily improving socio-economic status of the African countries. New Rice for Africa (NERICA), which are interspecific hybrids between Asian and African rice varieties, are one of successful breeding products utilizing biodiversity across the two different rice crop species. Upland NERICA varieties (NU) exhibit agronomic traits of value for the harsh eco-geography, including shorter duration, higher yield and stress tolerance, compared to local African varieties. However, the molecular basis of the traits in NU varieties is largely unknown. Results Whole genome re-sequencing was performed of four NU lines (3, 4, 5, and 7) and for the parental Oryza sativa WAB56–104 and Oryza glaberrima CG14. The k-mer analysis predicted large genomes for the four NU lines, most likely inherited from WAB56–104. Approximately 3.1, 0.10, and 0.40 million single nucleotide polymorphisms, multi nucleotide polymorphisms, and short insertions/deletions were mined between the parental lines, respectively. Integrated analysis with another four NU lines (1, 2, 8, and 9) showed that the ratios of the donor CG14 allelic sites in the NU lines ranged from 1.3 to 9.8%. High resolution graphical genotype indicated genome-level similarities and common genetic events during the breeding process: five xyloglucan fucosyltransferase from O. glaberrima were introgressed in common. Segregation of genic segments revealed potential causal genes for some agronomic traits including grain shattering, awnness, susceptibility to bacterial leaf bright, and salt tolerance. Analysis of unmapped sequences against the reference cultivar Nipponbare indicated existence of unique genes for pathogen and abiotic stress resistance in the NU varieties. Conclusions The results provide understanding of NU genomes for rice improvement for Africa reinforcing local capacity for food security and insights into molecular events in breeding of interspecific hybrid crops.

Class II high-affinity potassium transporters (HKT2s) mediate Na+–K+ cotransport and Na+/K+ homeostasis under K+-starved or saline conditions. Their functions have been studied in yeast and X. laevis oocytes; however, little is known about their respective properties in plant cells. In this study, we characterized the Na+ and K+ transport properties of SvHKT2;1, SvHKT2;2 and HvHKT2;1 in Arabidopsis under different ionic conditions. The differences were detected in shoot K+ accumulation and root K+ uptake under salt stress conditions, K+ accumulation in roots and phloem sap under K+-starved conditions, and shoot and root Na+ accumulation under K+-starved conditions among the HKT2s transgenic lines and WT plants. These results indicate the diverse ionic transport properties of these HKT2s in plant cells, which could not be detected using yeast or X. laevis oocytes. Furthermore, Arabidopsis expressing HKT2s showed reduced salt tolerance, while over-expression of HvHKT2;1 in barley, which has the ability to sequestrate Na+, showed enhanced salt tolerance by accumulating Na+ in the shoots. These results suggest that the coordinated enhancement of Na+ accumulation and sequestration mechanisms in shoots could be a promising strategy to confer salt tolerance to glycophytes.

The Arabidopsis high-affinity K+ transporter (AtHKT1;1) plays roles in salt tolerance by unloading Na+ from the root xylem to the xylem parenchyma cells and/or uploading Na+ from the shoot/leaf xylem to the xylem parenchyma cells. To use this promoter for the molecular breeding of salt-tolerant plants, I evaluated the expression profile of the AtHKT1;1 promoter in detail. Approximately 1.1 kbp of sequence upstream from the start codon of AtHKT1;1 was polymerase chain reaction (PCR)-amplified, fused to the β-glucuronidase (GUS) gene, and introduced into Arabidopsis. The resultant transformants were evaluated under nonstressed and salt-stress conditions at the seedling and reproductive stages. Histochemical analysis showed that GUS activity was detected in vascular bundle tissue in roots, hypocotyls, petioles, leaves, and petals, and in root tips. GUS enzyme activity in shoots tended to be higher than that in roots at both stages. After treatment with 50 mM NaCl for 24 h, GUS transcription levels and GUS enzyme activity were enhanced in transgenic lines. These results indicate that the AtHKT1;1 promoter isolated in this study could be useful in expressing transgenes specifically in vascular tissue and root tips, and in a mild salt-stress-responsive manner. The data provide novel insights into the functions of AtHKT1;1.

We produced transgenic Arabidopsis plants that express chimeric genes for transcription factors converted to dominant repressors, using Chimeric REpressor gene-Silencing Technology (CRES-T), and evaluated the salt tolerance of each line. The seeds of the CRES-T lines for ADA2b, Msantd, DDF1, DREB26, AtGeBP, and ATHB23 exhibited higher germination rates than Wild type (WT) and developed rosette plants under up to 200 mM NaCl or 400 mM mannitol. WT plants did not grow under these conditions. In these CRES-T lines, the expression patterns of stress-related genes such as RD29A, RD22, DREB1A, and P5CS differed from those in WT plants, suggesting the involvement of the six transcription factors identified here in the stress response pathways regulated by the products of these stress-related genes. Our results demonstrate additional proof that CRES-T is a superior tool for revealing the function of transcription factors.

A chimeric gene containing the gene encoding beta-glucuronidase regulated by the pyruvate,orthophosphate dikinase (PPDK) promoter from a maize C4 plant is introduced into a C3 cereal, rice. The gene is only expressed in photosynthetic organs, leaf blades and sheaths. A protein which binds a cis-acting element of the C4-type gene that interacts with DNA-binding rice proteins and resembles a maize nuclear protein that binds PPDK in maize, is present in rice.

Salinity stress, which induces both ionic and osmotic damage, impairs plant growth and causes severe reductions in crop yield. Plants are equipped with defense responses against salinity stress such as regulation of ion transport including Na+ and K+, accumulation of compatible solutes and stress-related gene expression. The initial Ca2+ influx mediated by plasma membrane ion channels has been suggested to be crucial for the adaptive signaling. NADPH oxidase (Nox)-mediated production of reactive oxygen species (ROS) has also been suggested to play crucial roles in regulating adaptation to salinity stress in several plant species including halophytes. Respiratory burst oxidase homolog (Rboh) proteins show the ROS-producing Nox activity, which are synergistically activated by the binding of Ca2+ to EF-hand motifs as well as Ca2+-dependent phosphorylation. We herein review molecular identity, structural features and roles of the Ca2+-permeable channels involved in early salinity and osmotic signaling, and comparatively discuss the interrelationships among spatiotemporal dynamic changes in cytosolic concentrations of free Ca2+, Rboh-mediated ROS production, and downstream signaling events during salinity adaptation in planta. [ABSTRACT FROM AUTHOR]

Abstract  To establish a procedure for Agrobacterium tumefaciens-mediated transformation of golden pothos (Epipremnum aureum) plants, the effects of selection antibiotics and the preculture period of stem explants before A. tumefaciens infection were examined. Explants were co-cultivated with A. tumefaciens EHA105, harboring the plasmid pGWB2/cGUS, on a somatic embryo-inducing medium supplemented with acetosyringone. Resulting transgenic somatic embryos were screened on an antibiotic selection medium, and the transgenic pothos plants were regenerated on a germination medium. Hygromycin was the optimum selection antibiotic tested. The preculture period significantly affected the transformation efficiency, with explants precultured for one-day showing the best efficiency (5–30%). Both transformed hygromycin-resistant embryos and regenerated plants showed β-glucuronidase activity. Southern blot analysis confirmed transgene integration into the pothos genome. This reproducible transformation system for golden pothos may enable the molecular breeding of this very common indoor plant. [ABSTRACT FROM AUTHOR]

Abstract  We investigated the transcriptional response of Burma mangrove (Bruguiera gymnorhiza) to high salinity (salt stress; 500 mM NaCl) and hyperosmotic stress (osmotic stress; 1 M sorbitol) by microarray analysis. ANOVA (P + and Cl−, even under non-stressed conditions; to uptake additional Na+ and Cl− for use as osmolytes; and to maintain K+ homeostasis under salt stress. [ABSTRACT FROM AUTHOR]

The correct choice of process parameters is important in predicting the cut surface and obtaining a fully-fine sheared surface in the fine blanking process. The researchers used the value of the critical fracture criterion obtained by long duration experiments to predict the conditions of cut surfaces in the fine blanking process. In this study, the clearance-dependent critical ductile fracture criteria obtained by the Cockcroft-Latham and Oyane criteria were used to reduce the time and cost of experiments to obtain the value of the critical fracture criterion. The Finite Element Method (FEM) was applied to fine blanking processes to study the influences of process parameters such as the initial compression, the punch and die corner radii and the shape and size of the V-ring indenter on the length of the sheared surface. The effects of stress triaxiality and punch diameters on the cut surface produced by the fine blanking process are also discussed. The verified process parameters and tool geometry for obtaining a fully-fine sheared SPCC surface are described. The results showed that the accurate and stable prediction of ductile fracture initiation can be achieved using the Oyane criterion.

Punching processes are widely used for producing automobile parts, mechanical components, and other parts. To produce highly accurate parts, it is important to estimate the ratio of the sheared surface to the cut surface. Many researchers have applied the finite-element method (FEM) to analyze the ratio of the sheared surface to the fracture surface on cut surfaces by using ductile fracture criteria. However, it is difficult to determine the fracture criteria on the cut surface by tensile tests or bending tests because the punching process involves many complicated steps. In this study, FEM was applied to the punching process to determine the values of critical fracture criteria (C) by using the ductile fracture criteria proposed by Cockcroft and Latham, Oyane, and Ayada. The ductile fracture criteria were compared with the boundary between the shear surface and the fracture surfaces using experiments performed with a simple punching system. The values of the ductile fracture criteria for the fracture initiation of the formed cut surface were predicted under various clearances between the punch and the die with various punch diameters. The influence of stress triaxiality and the effect of punch diameter on the sheared surface length are also discussed.

To identify key proteins in the regulation of salt tolerance in the mangrove plant Bruguiera gymnorhiza, proteome analysis of samples grown under conditions of salt stress was performed. Comparative two-dimensional electrophoresis revealed that two, three and one protein were differentially expressed in the main root, lateral root and leaf, respectively, in response to salt stress. Among these, three proteins were identified by internal peptide sequence analysis: fructose-1,6-bisphosphate (FBP) aldolase and a novel protein in the main root, and osmotin in the lateral root. These results suggest that FBP aldolase and osmotin play roles in salt tolerance mechanisms common to both glycophytes and mangrove plants. Osmotin was abundant at early time points following salt treatment and seems to play a role in initial osmotic adaptation in lateral roots of B. gymnorhiza under salt stress, but does not contribute towards adaptation to prolonged or continuous exposure to salt stress. The amounts of these proteins were not correlated with those of the respective mRNAs, as determined by microarray analysis. A novel salt-responsive protein, not previously detected by expressed sequence tag analysis or transcriptome analysis, was also identified in this proteomic approach, and may provide insight into the salt tolerance mechanism of the mangrove plant. This is the first report of proteome analysis with detailed analysis of main and lateral roots of mangrove plants under salt stress conditions. [ABSTRACT FROM AUTHOR]