Evidence of heterogeneous selection on quantitative traits of Prosopis flexuosa (Leguminosae) from multivariate Q ST –F ST test

Prosopis flexuosa is an arboreal Leguminosae that grows in arid and semiarid temperate zones of Argentina, in the Monte eco-region. It is a promising native forest species for recovering arid and semiarid regions because it plays an important role in erosion control as well as in soil fertility. Furthermore, it provides diverse economical resources. The main challenge to the forestry sector is finding a balance between production and forest protection. For this purpose, it is necessary to gather information about genetic parameters. In this study, we measured the distribution of the variation of 14 quantitative traits in an experimental half-sib stand, where families are representative of hierarchically structured populations. We applied a multivariate extension of the classical Q _ST –F _ST neutrality test to determine the relative importance of drift versus selection in the distribution of genetic variability. We found strong evidence that different selective regimes act on different traits and that selection favors different optima in each sampling site. The selection to different optima is much stronger among than within provenances. This result helps explain the possible causes for the regional variation observed in P. flexuosa and to define the management units and the evolutionarily significant units for this species.     

First comparative phenetic studies of Argentinean species of Acacia (Fabaceae), using morphometric, isozymal, and RAPD approaches

Morphological and genetic diversity among Acacia aroma, A. macracantha, A. caven, and A. furcatispina were studied with morphometric, isozymal, and RAPD approaches. The analysis of seven isozyme systems revealed 21 loci, and RAPD analysis showed 34 loci. Most of these loci allowed us to differentiate the species, with the exception of A. aroma and A. macracantha, the two most similar species. The levels of genetic variability estimated by isozymes were higher than those obtained from RAPD analyses. Morphometric characters showed highly significant differences among the species, although A. aroma and A. macracantha are differentiated only by thorn length. The phenogram obtained from isozyme data is consistent with morphological data. The RAPD phenogram based on allelic frequencies showed agreement with morphological and isozymal approaches only at the intraspecific levels, while the RAPD phenogram based on Nei and Li's similarity measures agreed with the phenograms constructed from isozyme and morphological data. High similarities and high indirect gene flow were found between A. aroma and A. macracantha, results that call the relationship between them into question.     

Mating system and population structure of Acacia aroma and A. macracantha (Fabaceae)

Acacia aroma and A. macracantha are closely related species that inhabit northern and central Argentina. The reproductive barriers between them seem to be weak. They exhibit low genetic differentiation, high levels of interspecific gene flow, and extensive areas of sympatry. Isoenzymatic approaches were used to evaluate the population structure and mating system parameters in natural Argentine populations of A. aroma and A. macracantha and to provide new tools for the analysis of relationships between these two species. All studied populations had high levels of genetic variability and no significant departures from Hardy-Weinberg expectations, but the two species did not differ from each other. Most variability occured within populations. Mating system analysis showed high levels of outcrossing, no biparental inbreeding, and a high probability that individuals within progeny arrays are full rather than half sibs. In all A. aroma and A. macracantha populations, polymorphic loci had the same allelic variants, and no geographic or genetic isolation between species was found. The results favor the hypothesis that these two entities represent a single polymorphic species rather than two distinct species.     

Durability of five native Argentine wood species of the genera <Emphasis Type="Italic">Prosopis</Emphasis> and <Emphasis Type="Italic">Acacia</Emphasis> decayed by rot fungi and its relationship with extractive content

The natural durability of four Argentinean species of Prosopis and one of Acacia was evaluated in laboratory tests, according to European standards, using three brown rot and one white rot fungi. These tests were complemented by assessing the wood chemical composition. All the species were from moderately slightly durable to very durable (classes 4–1), and in all cases the heartwood was the most resistant to fungal attack. Chemical extractives content (organic, aqueous, tannic and phenolic) was higher in the heartwood. However, species durability was not related to extractive contents nor with wood density. Instead, it is possible that extractives could contribute to natural durability in different ways, including the effects related to the antioxidant properties of some of them.     

Genetically modified HLA class I molecules able to inhibit human NK cells without provoking alloreactive CD8+ CTLs

Human NK cells are likely to be important effectors of xenograft rejection. Expression of HLA class I molecules by transfected porcine cells can protect them from human NK cell-mediated lysis; however, this strategy has the potential to augment the anti-graft response by recipient CD8(+) T cells recognizing foreign pig peptides presented by HLA. In this study we show that the introduction of a mutation (D227K) in the alpha(3) domain of HLA-Cw3 abrogates its recognition by CD8-dependent T cells but leaves intact its ability to function as an inhibitory ligand for NK cells. Such genetically modified molecules may have potential therapeutic applications in the prevention of delayed xenograft rejection and in the facilitation of allogeneic and xenogeneic bone marrow engraftment.     

Morphologic and immunophenotypic characterization of a cell line derived from liver tissue with epstein-barr virus associated post-transplant lymphoproliferative disease

Summary A B-cell line was established from the liver of an 11-yr-old boy with Epstein-Barr virus (EBV)-associated post-transplant lymphoproliferative disease (PTLD). The cells were morphologically heterogenous, CD10 (CALLA) negative, and expressed several B-cell antigens, including CD23, in a manner reminiscent of lymphoblastoid cell lines (LCLs) reported in the literature. However, the cells also showed expression of the CD77 antigen, carried a 14q32+ chromosomal anomaly, and showed IgM-kappa immunoglobulin isotype restriction immediately after their outgrowth in culture. These latter properties are typically associated with Burkitt’s lymphoma cell lines rather than LCLs. Aberrant expression of the L60 antigen on these B-cells was found as additional evidence of altered growth regulation in these cells. EBV infection was demonstrated by the abundant expression of EBNA-2 and LMP viral antigens in culture. The cell line described should be useful in planning in vitro experiments designed to understand the factors that modulate the growth of PTLD in vivo.     

Mating system parameters in species of genus Prosopis (Leguminosae)

The section Algarobia of genus Prosopis involves important natural resources in arid and semiarid regions of the world. Their rationale use requires a better knowledge of their biology, genetics and mating system. There are contradictory information about their mating system. Some authors claim they are protogynous and obligate outcrosser. However, some evidence have been shown indicating that they might not be protogynous and that they might be somewhat self-fertile. The current paper analyses genetic structure and mating system parameters in populations of seven species of this section from South and North America based on isozyme data. In all species a significant homozygote excess was found in the offspring population but not in mother plant genotypes. Multilocus and mean single locus outcrossing rates (tm, ts) indicated that about 15% selfing can occur in the studied populations. The heterogeneity between pollen and ovule allele frequencies was low suggesting population structuration, in agreement with the estimates of correlation of tm within progeny (rt) and correlation of outcrossed paternity (rp). The difference of FIS estimates between offspring and mother plants suggest some selection favouring heterozygotes between seedling and adult stages.