Forest-tree genetics research:Quercus L.

Oaks are the sources, not only of the most valuable timber among broad- leaved trees of the northern hemisphere, but also of cork, tannin, a dye, and food for man and beast. Their prolonged pre-flowering periods and other factors have discouraged genetic investigation of them, but what little is known in that direction is here summarized.     

Developmental quantitative genetics of growth in Populus

 Nursery growth and dry weight were analyzed for F₂ genotypes derived from Populus trichocarpa×P. deltoides that have been field tested with clonal replicates in three different environments. The correlations between nursery and plantation performance differed among the environments, with higher values at Boardman and Clatskanie (both planted with rooted cuttings) than Puyallup (planted with unrooted cuttings). At Puyallup, nursery height was more strongly associated with plantation growth than were nursery diameter and dry weight. Yet, this finding was not supported by QTL mapping. A single overdominant QTL on linkage group G affected the stem height of both seedlings and resprouts in the nursery but showed nonsignificant LOD scores for plantation height from ages 1 to 5 at Puyallup. A total of four QTLs were identified for nursery diameter, one of which on linkage group O also controlled plantation basal area at all ages. Two important nursery QTLs on linkage groups B and G were used to estimate the relative efficiency of marker-assisted selection for plantation productivity. Despite the fact that they were not detected in the plantation stage, these two QTLs could significantly increase the proportion of the phenotypic variance explained by plantation QTLs. Received: 5 February 1998 / Accepted: 1 April 1998     

Molecular population genetics of elicitor-induced resistance genes in European aspen (Populus tremula L., Salicaceae)

Owing to their long life span and ecological dominance in many communities, forest trees are subject to attack from a diverse array of herbivores throughout their range, and have therefore developed a large number of both constitutive and inducible defenses. We used molecular population genetics methods to examine the evolution of eight genes in European aspen, Populus tremula, that are all associated with defensive responses against pests and/or pathogens, and have earlier been shown to become strongly up-regulated in poplars as a response to wounding and insect herbivory. Our results show that the majority of these defense genes show patterns of intraspecific polymorphism and site-frequency spectra that are consistent with a neutral model of evolution. However, two of the genes, both belonging to a small gene family of polyphenol oxidases, show multiple deviations from the neutral model. The gene PPO1 has a 600 bp region with a highly elevated K(A)/K(S) ratio and reduced synonymous diversity. PPO1 also shows a skew toward intermediate frequency variants in the SFS, and a pronounced fixation of non-synonymous mutations, all pointing to the fact that PPO1 has been subjected to recurrent selective sweeps. The gene PPO2 shows a marked excess of high frequency, derived variants and shows many of the same trends as PPO1 does, even though the pattern is less pronounced, suggesting that PPO2 might have been the target of a recent selective sweep. Our results supports data from both Populus and other species which have found that the the majority of defense-associated genes show few signs of selection but that a number of genes involved in mediating defense against herbivores show signs of adaptive evolution.     

Genetic linkage mapping in aspen (Populus tremula L. and Populus tremuloides Michx.)

A large number of simple sequence repeat (SSR) marker-containing genetic maps are available for several Populus species. For aspen however, no SSR-containing map has been published so far. In this study, genetic linkage mapping was carried out with an interspecific mapping pedigree of 61 full-sib hybrids of European × quaking aspen (Populus tremula L. × Populus tremuloides Michx.), using the two-way pseudo-testcross strategy. Amplified fragment-length polymorphism (AFLP) and SSR markers were used for mapping, resulting in the first SSR-containing genetic linkage maps for aspen. The maps allow comparisons with a Populus consensus map and other published genetic maps of the genus Populus. The maps showed good collinearity to each other and to the Populus consensus map and provide a direct link to the Populus trichocarpa genomic sequence. Sex as a morphological trait was assessed in the mapping population and mapped on a non-terminal position of linkage group XIX on the male P. tremuloides map.     

Molecular population genetics of herbivore-induced protease inhibitor genes in European aspen (Populus tremula L., Salicaceae)

Plants defend themselves against the attack of natural enemies by using an array of both constitutively expressed and induced defenses. Long-lived woody perennials are overrepresented among plant species that show strong induced defense responses, whereas annual plants and crop species are underrepresented. However, most studies of plant defense genes have been performed on annual or short-lived perennial weeds or crop species. Here I use molecular population genetic methods to survey six wound-inducible protease inhibitors (PIs) in a long-lived woody, perennial plant species, the European aspen (Populus tremula), to evaluate the likelihood of either recurrent selective sweeps or balancing selection maintaining amino acid polymorphisms in these genes. The results show that none of the six PI genes have reduced diversities at synonymous sites, as would be expected in the presence of recurrent selective sweeps. However, several genes show some evidence of nonneutral evolution such as enhanced linkage disequilibrium and a large number of high-frequency-derived mutations. A group of at least four Kunitz trypsin inhibitor genes appear to have experienced elevated levels of nonsynonymous substitutions, indicating allelic turnover on an evolutionary timescale. One gene, TI1, has enhanced levels of intraspecific polymorphism at nonsynonymous sites and also has an unusual haplotype structure characterized by two divergent haplotypes occurring at roughly equal frequencies in the sample. One haplotype has very low levels of intraallelic nucleotide diversity, whereas the other haplotype has levels of diversity comparable to other genes in P. tremula. Patterns of sequence diversity at TI1 do not fit a simple model of either balancing selection or recurrent selective sweeps. This suggests that selection at TI1 is more complex, possibly involving allelic cycling.     

Molecular genetics of growth and development in Populus. I. Triploidy in hybrid poplars

Summary While constructing a genetic linkage map of a hybrid poplar genome (Populus trichocarpa x P. deltoides), we identified several restriction fragment length polymorphismus (RFLPs) for which the parental trees are heterozygous. Although 8 of the 11 F₁ hybrid offspring inherited, as expected, single RFLP alleles from each parent, 3 F₁ trees in the mapping pedigree inherited both maternal alleles along with a single paternal allele at some loci. Aneuploidy or polyploidy in these 3 F₁ trees due to partial or complete nondisj unction during female gametogenesis is the simplest explanation for this finding. Of the 3 f₁ offspring with supernumerary RFLP alleles 2 have triploid nuclear DNA contents as measured by fluorescence flow cytometry; the 3rd F₁ with supernumerary alleles has a sub-triploid nuclear DNA content and is probably aneuploid. Among the tri/aneuploid hybrids, leaf quantitative traits either are skewed toward those values characteristic of the P. trichocarpa female parent (adaxial stomate density, petiole length: blade length ratio; abaxial color) or show transgressive variation (epidermal cell size). Abaxial leaf color was used to screen a large population of P. trichocarpa x P. deltoides hybrids for further evidence of tri/aneuploidy. In each case where a white abaxial leaf surface was observed and the nuclear DNA content measured, the hybrid proved to be tri/aneuploid. All sexually mature female triploids examined were sterile, although the inflorescences completed their development in the absence of embryo formation. The (probably) aneuploid F₁ hybrid is a fertile female. Of 15 female P. trichocarpa parents used in crosses to P. deltoides, 10 produced one or more tri/aneuploid hybrid offspring. In an intraspecific cross using a P. trichocarpa female that had produced triploid hybrids with five different P. deltoides males, no tri/aneuploid offpsring were found.     

Arsenic tolerance and phytoremediation potential of Conocarpus erectus L. and Populus deltoides L.

The present study was conducted to explore arsenic (As) tolerance and phytostabilization potential of the two tree species, buttonwood (Conocarpus erectus) and eastern cottonwood (Populus deltoides). Both plant species were grown in pots and were exposed to various soil As levels (control, 5, 10, 15, and 20 mg kg^?1). The plants were harvested after 9 months for the evaluation of growth parameters as well as root and shoot As concentrations. With increasing soil As levels, plant height stress tolerance index (PHSTI) was significantly decreased in both tree species, whereas root length stress tolerance index (RLSTI) and dry matter stress tolerance index (DMSTI) were not affected. Root and shoot As concentrations significantly increased in both tree species with increasing soil As levels. Translocation factor and bioconcentration factor were less than 1.0 for both plant species. This study revealed that both tree species are non-hyperaccumulators of As, but they could be used for phytostabilization of As-contaminated soils.     

Molecular genetics of growth and development in Populus. II. Segregation distortion due to genetic load

Distortion of expected Mendelian segregation ratios, commonly observed in many plant taxa, has been detected in an experimental three-generation inbred pedigree of Populus founded by interspecific hybridization between P. trichocarpa and P. deltoides. An RFLP linkage map was constructed around a single locus showing severe skewing of segregation ratio against F₂ trees carrying the P. trichocarpa allele in homozygous form. Several hypotheses for the mechanism of segregation distortion at this locus were tested, including directional chromosome loss, segregation of a pollen lethal allele, conflicts between genetic factors that isolate the parental species, and inbreeding depression as a result of genetic load. Breeding experiments to produce inbred and outcrossed progenies were combined with PCR-based detection of RFLPs to follow the fate of the deficient allele throughout embryo and seedling development. A recessive lethal allele, lth, inherited from the P. trichocarpa parent, was found to be tightly linked to the RFLP marker locus POP1054 and to cause embryo and seedling mortality. Heterozygotes (lth/+) appear to be phenotypically normal as embryos, seedlings, and young trees.Abbreviations RFLP restriction fragment length polymorphism - PCR polymerase chain reaction - STS sequence-tagged site - SDS sodium dodecyl sulfate     

Xenopus research: metamorphosed by genetics and genomics

Research using Xenopus takes advantage of large, abundant eggs and readily manipulated embryos in addition to conserved cellular, developmental and genomic organization with mammals. Research on Xenopus has defined key principles of gene regulation and signal transduction, embryonic induction, morphogenesis and patterning as well as cell cycle regulation. Genomic and genetic advances in this system, including the development of Xenopus tropicalis as a genetically tractable complement to the widely used Xenopus laevis, capitalize on the classical strengths and wealth of achievements. These attributes provide the tools to tackle the complex biological problems of the new century, including cellular reprogramming, organogenesis, regeneration, gene regulatory networks and protein interactions controlling growth and development, all of which provide insights into a multitude of human diseases and their potential treatments.     

Osservazioni sul comportamento sessuale del Populus tremula L. in Italia

Abstract

OBSERVATIONS ON SEXUAL BEHAVIOUR OF POPULUS TREMULA L. IN ITALY. — A research has been carried on sex distribution of Populus tremula in Italy. On 101 observed populations the sexual ratio resulted of 2:1 in favour of male sex. The analysis of results referred to the two geographycal sectors of the peninsula, North and MiddleSouth, is however showing some discordant data in the sexual composition of several populations. In North-Italy the ratio results of 2,5:1 in favour of male sex, in MiddleSouth 1:1.

These discordant results would show that male sex can be adapted whether in continental or in mountain climate.

The Author deems that the geographycal position of populations and corresponding climatic characteristics can be responsible for the sexual selection, so that the several deviations wich are found in natural populations of P. tremula can get an explanation in an possible correlation between habitat and sex.

The Author dwells particulary upon population discovered at Campiglione, near Pozzuoli (Naples). Stamens, varying in number from 2 to 4, were observed on almost all the pistillate flowers of every single catkin of these individuals and especially from the base to a little over halfway up the catkin.

The high proportion of bisexual catkins found on every individual examined leads to the conclusion that P. tremula is « polygamo-dioecious » in character, that is, it produces bisexual and unisexual character in the case of P. tremuloides, where, however, in the majority of the bisexual individuals, the percentage of hermaphrodite flowers on one catkin was very small (1–2%).

These cases of bisexuality lead one to thing that dioecism is an acquired character in the genus Populus. This condition (wich, at least in the case of P. tremula, is perhaps to be connected with the poor fertility of the species) could in time have lead to the present geographycal distribution in colonies of isolated and sexually anbalanced individuals.

These cold have survived to our times due to their aptitude vegetative propagation by means of suckers, giving rise to scattered clumps of unisexual individuals of the same clone. The finding of these bisexual individuals is of considerable importance for applied genetics, and could initiate new researches in Italy to obtain genotypic and polyploid descendants.     

杨属（PopulusL.）种质资源遗传学评价研究进展

杨属（PopulusL.）种质资源极其丰富,为了有效保存、合理利用杨属种质资源,国内外开展了大量的种质资源遗传学评价研究。该文在介绍杨树系统分类的基础上,概述了白杨派、青杨派和黑杨派等在生物学特性、抗性（耐盐、抗旱、抗冻及抗病虫）、适应性及DNA遗传多态性等方面的遗传学评价研究进展,重点讨论了杨树种质资源评价研究中存在的问题和不足,并对其研究前景进行了展望。     

钻天杨的组织培养与植株再生

1植物名称钻天杨(Populus nigra L.var.italica)。2材料类别无菌苗叶片。3培养条件(1)芽分化培养基:MS TDZ 0.1 mg·L~(-1)(单位下同) NAA 0.01;(2)生根培养基:1/2MS IBA 0.5;上述培养基中均加入0.7%琼脂和2%蔗糖,pH 5.8。培养基在121℃条件下灭菌20 min。培养温度为(25±2)℃,每天光照和暗     

Genetic fatalism and social policy: the implications of behavior genetics research.

Recent advances in molecular genetics methods have provided new means of determining the genetic bases of human behavioral traits. The impetus for the use of these approaches for specific behaviors depends, in large part, on previous familial studies on inheritance of such traits. In the past, a finding of a genetic basis for a trait was often accompanied with the idea that that trait is unchangeable. We discuss the definition of "genetic trait" and heritability and examine the relationship between these concepts and the malleability of traits for both molecular and nonmolecular approaches to behavioral genetics. We argue that the malleability of traits is as much a social and political question as it is a biological one and that whether or not a trait is genetic has little relevance to questions concerning determinism, free will, and individual responsibility for actions. We conclude by noting that "scientific objectivity" should not be used to conceal the social perspectives that underlie proposals regarding social change.     

Large scale geographic clines of parasite damage to Populus tremula L.

According to the geographic mosaic theory of coevolution (GMTC), clines of traits reflecting local co‐adaptation (including resistance genes) should be common between a host and its parasite and should persist across time. To test the GMTC‐assumption of persistent clinal patterns we compared the natural prevalence of two parasites on aspen Populus tremula trees: mining moths of the genus Phyllocnistis and leaf rust Melampsora spp. Damage data were collated from the Swedish National Forest Damage Inventory (2004–2006). In addition, occurrence of the parasites was scored in field conditions in two common gardens in the north and south of Sweden over five growing seasons (2004–2008), then related to biomass (stem height and diameter) and to concentrations of eleven leaf phenolics. Phyllocnistis mainly occurred in the northern garden, a distribution range which was confirmed by the countrywide inventory, although Phyllocnistis was more abundant on southern clones, providing evidence for possible local maladaptation. Melampsora occurred all over the country and in both gardens, but built up more quickly on northern clones, which suggests a centre of local clone maladaptation in the north. Stem growth also followed a clinal pattern as did the concentration of three phenolic compounds: benzoic acid, catechin and cinnamic acid. However, only benzoic acid was related to parasite presence: negatively to Phyllocnistis and positively to Melampsora and it could thus be a potential trait under selection. In conclusion, clines of Phyllocnistis were stronger and more persistent compared to Melampsora, which showed contrasting clines of varying strength. Our data thus support the assumption of the GMTC model that clines exist in the border between hot and cold spots and that they may be less persistent for parasites with an elevated gene flow, and/or for parasites which cover relatively larger hot spots surrounded by fewer cold spots.