Relationships between grain protein content and grain yield components through quantitative trait locus analyses in a recombinant inbred line population derived from two elite durum wheat cultivars

Grain protein content (GPC) in durum wheat (Triticum turgidum var. durum) is negatively correlated with grain yield. To evaluate possible genetic interrelationships between GPC and grain yield per spike, thousand-kernel weight and kernel number per spike, quantitative trait loci (QTL) for GPC were mapped using GPC-adjusted data in a covariance analysis on yield components. Phenotypic data were evaluated in a segregating population of 120 recombinant inbred lines derived from crossing the elite cultivars Svevo and Ciccio. The material was tested at five environments in southern Italy. QTL were determined by composite interval mapping based on the Svevo?×?Ciccio linkage map described in Gadaleta et al. (2009) and integrated with DArT markers. The close relationship between GPC and yield components was reflected in the negative correlation between the traits and in the reduction of variance when GPC values were adjusted to yield components. Ten independent genomic regions involved in the expression of GPC were detected, six of which were associated with QTL for one or more grain yield components. QTL alleles with increased GPC effects were associated with QTL alleles with decreased effects on one or more yield component traits, or vice versa (i.e. the allelic effects were in opposite direction). Four QTL for GPC showed always significant effects, and these QTL should represent genes that influence GPC independently from variation in the yield components. Such genes are of special interest in wheat breeding since they would allow an increase in GPC without a concomitant decrease in grain yield.     

Doppel is an N-glycosylated, glycosylphosphatidylinositol-anchored protein. Expression in testis and ectopic production in the brains of Prnp(0/0) mice predisposed to Purkinje cell loss

The Prnd gene encodes a homolog of the cellular prion protein (PrP(C)) called doppel (Dpl). Up-regulation of Prnd mRNA in two distinct lines of PrP gene ablated (Prnp(0/0)) mice, designated Rcm0 and Ngsk, is associated with death of Purkinje cells. Using recombinant Dpl expressed in Escherichia coli and mouse neuroblastoma cells we demonstrate that wild type (wt) Dpl, like PrP(C), adopts a predominantly alpha-helical conformation, forms intramolecular disulfide bonds, has two N-linked oligosaccharides, and is presented on the cell surface via a glycosylphosphatidylinositol anchor. Dpl protein was detected in testis of wt mice. Using Triton X-114 phase partitioning to enrich for glycosylphosphatidylinositol-anchored proteins, Dpl was detected in brain samples from Rcm0 Prnp(0/0) mice but was absent in equivalent samples from wt mice and ZrchI Prnp(0/0) mice, indicating that ectopic expression of this protein may cause cerebellar pathology in Rcm0 mice. Biochemical and structural similarities between PrP(C) and Dpl documented here parallel the observation that ataxic Ngsk Prnp(0/0) mice can be rescued by overexpression of wild-type PrP transgenes, and suggest that cell surface PrP(C) can antagonize the toxic effect of Dpl expressed in the central nervous system.     

The Activator of Apoptosis Smac-DIABLO Acts as a Tetramer in Solution

Smac-DIABLO in its mature form (20.8 kDa) binds to baculoviral IAP repeat (BIR) domains of inhibitor of apoptosis proteins (IAPs) releasing their inhibitory effects on caspases, thus promoting cell death. Despite its apparent molecular mass (∼100 kDa), Smac-DIABLO was held to be a dimer in solution, simultaneously targeting two distinct BIR domains. We report an extensive biophysical characterization of the protein alone and in complex with the X-linked IAP (XIAP)-BIR2-BIR3 domains. Our data show that Smac-DIABLO adopts a tetrameric assembly in solution and that the tetramer is able to bind two BIR2-BIR3 pairs of domains. Our small-angle x-ray scattering-based tetrameric model of Smac-DIABLO/BIR2-BIR3 highlights some conformational freedom of the complex that may be related to optimization of IAPs binding.     

Chromosome numbers and meiotic analysis in the pre-breeding of <Emphasis Type="BoldItalic">Brachiaria decumbens</Emphasis> (Poaceae)

A total of 44 accessions of Brachiaria decumbens were analysed for chromosome count and meiotic behaviour in order to identify potential progenitors for crosses. Among them, 15 accessions presented 2n = 18; 27 accessions, 2n = 36; and 2 accessions, 2n = 45 chromosomes. Among the diploid accessions, the rate of meiotic abnormalities was low, ranging from 0.82% to 7.93%. In the 27 tetraploid accessions, the rate of meiotic abnormalities ranged from 18.41% to 65.83%. The most common meiotic abnormalities were related to irregular chromosome segregation, but chromosome stickiness and abnormal cytokinesis were observed in low frequency. All abnormalities can compromise pollen viability by generating unbalanced gametes. Based on the chromosome number and meiotic stability, the present study indicates the apomictic tetraploid accessions that can act as male genitor to produce interspecific hybrids with B. ruziziensis or intraspecific hybrids with recently artificially tetraploidized accessions.