Nuclear-cytoplasmic male-sterility in diploid dandelions

Male-sterility was found in diploid dandelions from two widely separated populations from France, and its inheritance was analysed by crossing a diploid male-sterile dandelion to diploid sexuals and triploid apomicts. Nuclear genetic variation, found in full-sib families, segregated for male-fertility, partial male-sterility, and full male-sterility, and also segregated for small-sized versus normally sized pollen. The crossing results are best explained by a cytoplasmic male-sterility factor in combination with two dominant restorer genes. Involvement of the cytoplasmic male-sterility factor was further investigated by chloroplast haplotyping. Male-sterility was exclusively associated with a rare chloroplast haplotype (designated 16b). This haplotype was found in seven male-sterile plants and one (apparently restored) male-fertile individual but does not occur in 110 co-existing male-fertile plants and not in several hundreds of individuals previously haplotyped. Apomicts with cytoplasmic male sterility were generated in some test crosses. This raises the question as to whether the male sterility found in natural dandelion apomicts, is of cytoplasmic or of nuclear genetic nature. As many breeding systems in Taraxacum are involved in shaping population structure, it will be difficult to predict the evolutionary consequences of nuclear-cytoplasmic male-sterility for this species complex.     

How to be early flowering: an evolutionary perspective

In wild and cultivated annual plant species, flowering time is an important life-history trait that coordinates the life cycle with local environmental conditions. Extensive studies on the genetic basis of flowering time in the model species Arabidopsis thaliana have revealed a complex genetic network that can detect environmental and internal signals. Based on this knowledge and on known pleiotropic effects associated with flowering time genes, we suggest that a natural shift towards an early-flowering life cycle might involve only particular functional regions in a limited number of genes. Our predictions are supported by genetic theories of adaptation and by recent data about genes associated with natural variation. We analyse the extent to which these predictions can also apply to crop species.     

Tolerance to oxidative stress is associated with both oxidative stress response and inherent growth in a fungal wheat pathogen

Reactive oxygen species are toxic byproducts of aerobic respiration that are also important in mediating a diversity of cellular functions. Reactive oxygen species form an important component of plant defenses to inhibit microbial pathogens during pathogen–plant interactions. Tolerance to oxidative stress is likely to make a significant contribution to the viability and pathogenicity of plant pathogens, but the complex network of oxidative stress responses hinders identification of the genes contributing to this trait. Here, we employed a forward genetic approach to investigate the genetic architecture of oxidative stress tolerance in the fungal wheat pathogen Zymoseptoria tritici. We used quantitative trait locus (QTL) mapping of growth and melanization under axenic conditions in two cross-populations to identify genomic regions associated with tolerance to oxidative stress. We found that QTLs associated with growth under oxidative stress as well as inherent growth can affect oxidative stress tolerance, and we identified two uncharacterized genes in a major QTL associated with this trait. Our data suggest that melanization does not affect tolerance to oxidative stress, which differs from what was found for animal pathogens. This study provides a whole-genome perspective on the genetic basis of oxidative stress tolerance in a plant pathogen.     

Plant sex determination and sex chromosomes

Sex determination systems in plants have evolved many times from hermaphroditic ancestors (including monoecious plants with separate male and female flowers on the same individual), and sex chromosome systems have arisen several times in flowering plant evolution. Consistent with theoretical models for the evolutionary transition from hermaphroditism to monoecy, multiple sex determining genes are involved, including male-sterility and female-sterility factors. The requirement that recombination should be rare between these different loci is probably the chief reason for the genetic degeneration of Y chromosomes. Theories for Y chromosome degeneration are reviewed in the light of recent results from genes on plant sex chromosomes.     

The inter-specific hybrid Silene latifolia x S. viscosa reveals early events of sex chromosome evolution

The dioecious plant species Silene latifolia has a sex determination mechanism based on an active Y chromosome. Here, we used inter-specific hybrids in the genus Silene to study the effects of gene complexes on the Y chromosome. If the function of Y-linked genes has been maintained in the same state as in the hermaphrodite progenitor species, it should be possible to substitute such genes by genes coming from a related hermaphrodite species. In the inter-specific hybrid, S. latifolia x S. viscosa, anthers indeed develop far beyond the early bilobal stage characteristic of XX S. latifolia female plants. The S. viscosa genome can thus replace the key sex determination gene whose absence abolishes early stamen development in females (loss of the stamen-promoting function, SPF), so that hybrid plants are morphologically hermaphrodite. However, the hybrids have two anther development defects, loss of adhesion of the tapetum to the endothecium, and precocious endothecium maturation. Both these defects were also found in independent Y-chromosome deletion mutants of S. latifolia. The data support the hypothesis that the evolution of complete gender dimorphism from hermaphroditism involved a major largely recessive male-sterility factor that created females, and the appearance of new, dominant genes on the Y chromosome, including both the well-documented gynoecium-suppressing factor, and two other Y specific genes promoting anther development.     

Beyond Arabidopsis. Translational biology meets evolutionary developmental biology

Developmental processes shape plant morphologies, which constitute important adaptive traits selected for during evolution. Identifying the genes that act in developmental pathways and determining how they are modified during evolution is the focus of the field of evolutionary developmental biology, or evo-devo. Knowledge of genetic pathways in the plant model Arabidopsis serves as the starting point for investigating how the toolkit of developmental pathways has been used and reused to form different plant body plans. One productive approach is to identify genes in other species that are orthologous to genes known to control developmental pathways in Arabidopsis and then determine what changes have occurred in the protein coding sequence or in the gene's expression to produce an altered morphology. A second approach relies on natural variation among wild populations or crop plants. Natural variation can be exploited to identify quantitative trait loci that underlie important developmental traits and, thus, define those genes that are responsible for adaptive changes. The possibility of applying comparative genomics approaches to Arabidopsis and related species promises profound new insights into the interplay of evolution and development.     

Expression analysis of stress responsive pathway genes linked to drought hardiness in an adapted crop, finger millet (Eleusine coracana)

Drought is one of the major stresses limiting plant growth and productivity. Drought tolerance is regulated by multiple plant traits and examining the tolerance mechanisms from adapted species would assist in identification of novel pathways and superior genes. Since cellular tolerance is one of the major traits in drought acclimation we made in this study, an attempt to prospect candidate genes associated with the trait in drought hardy crop plant, finger millet (Eleusine coracana (L.) Gaertn). A novel gravimetric approach was employed to simulate field level drought stress for examining stress responsiveness of a few selected genes implicated in different stress response pathways. Gene expression was studied initially by e-northern analysis, and subsequently in leaf tissues experiencing different levels of drought stress by semi-quantitative and quantitative RT-PCR. A few stress responsive genes identified include metallothionein, farnesylated protein ATFP6, protein phosphatase 2A, RISBZ4 and farnesyl pyrophosphate synthase which probably have crucial roles in imparting hardiness to finger millet. Taken together the results suggest that multiple cellular tolerance pathways operate in a coordinated manner in drought tolerant crops.     

Resistance of tomato line Hawaii7996 to Ralstonia solanacearum Pss4 in Taiwan is controlled mainly by a major strain-specific locus

Bacterial wilt caused by the soilborne bacterium Ralstonia solanacearum attacks hundreds of plant species, including many agriculturally important crops. Natural resistance to this disease has been found in some species and is usually inherited as a polygenic trait. In tomato, a model crop plant, genetic analysis previously revealed the involvement of several QTL (quantitative trait loci) controlling resistance and, in all of these studies with different strains of the pathogen, loci on chromosome 6 played the predominant role in controlling this trait. Using quantitative data collected from a greenhouse test F3 population, we identified a new locus on chromosome 12 that appears to be active specifically against a race 1 biovar 3 Pss4 bacterial strain endemic to Taiwan. Chromosome 6 still contributes significantly to the control of the resistance, and weaker associations of the trait to other regions of the genome are observed. These results are discussed in the context of current molecular knowledge about the strain specificity of disease resistance genes.     

Genetic dissection of seed shattering,agronomic, and color traits in American wildrice ( Zizania palustris var. interior L.) with a comparative map

A comparative map of American wildrice ( Zizania palustris var. interior L.) was used to identify loci controlling seed shattering, plant height, maturity, tiller number, plant habit, panicle length seed length, and color traits. Two to six significant quantitative-trait-loci (QTLs, P < 0.05) were detected for each trait evaluated, representing the first trait-mapping in wildrice. The chosen population was designed to emphasize the mapping of loci controlling the shattering trait, which is the most important trait in the management of this newly domesticated species. Three loci were detected that controlled the discretely categorized variation between shattering and non-shattering plants. Seed-shattering loci were detected and validated among the F(2) and F(3) generations. A multiple regression model with these three loci described 49.6% of the additive genetic variation. A genetic model with the same three loci including dominance and locus interactions predicted the shattering versus non-shattering phenotype at a success rate of 87%. The comparative map was based on mapped RFLP markers used in white rice ( Oryza sativa L.) and other grass species. Anchor loci provided a reference point for the identification of potential orthologous genes on the basis of white rice mutant loci and consensus grass species QTLs. Candidate orthologous loci were identified among all traits evaluated. The study underscores the benefits of extending trait analysis through comparative mapping, as well as challenges of QTL analysis in a newly domesticated species.     

植物的表型可塑性、异速生长及其入侵能力

表型可塑性是指同一个基因型对不同环境响应产生不同表型的特性,特定性状的可塑性本身可以遗传,也可以接受选择而发生进化。植物个体的异速生长是指生物体某一特征的相对生长速率不等于第二种特征的相对生长速率的特性,该特性是由物种的遗传性决定的一种固定特征,植物往往朝着最佳的异速生长曲线进化。植物特定基因型在不同环境下,诸如生物量分配和种群几何学上的一些表型差异,既可由异速生长造成,也可由表型可塑性造成。植物本身的异速生长是一种"外观可塑性",而异速生长曲线的改变才是真正的可塑性。植物的表型可塑性、异速生长对于入侵植物的适应具有重要意义。干扰等异质性生境下表型可塑性成为物种生存扩散的有利性状,表型可塑性强的物种更有可能成为广布种。植物本身的异速生长特性或其异速生长曲线的改变都能影响其入侵能力。     

Trait plasticity,not values,best corresponds with woodland plant success in novel and manipulated habitats

Aims The clustering of plants with similar leaf traits along environmental gradients may arise from adaptation as well as acclimation to heterogeneous habitat conditions. Determining the forces that shape plant leaf traits requires both linking variation in trait morphology with abiotic gradients and linking that trait variation with plant performance under varying abiotic conditions. Across the spectrum of plant types, shade-tolerant evergreen herbs are relatively low in trait plasticity, compared to deciduous and sun-adapted species. These plants employ stress-tolerant strategies for survival, which coincide with relatively static trait morphologies, slow growth and hence a lower ability to adjust to changing environmental conditions.Methods We investigate how the survival of two ecologically similar understory evergreen species, Asarum arifolium and Hepatica nobilis, corresponds with variation in six commonly measured functional traits (leaf area, specific leaf area, plant height, leaf number, leaf length and shoot mass) along natural and experimental abiotic gradients. We examine temporal (the period 2007–9) and spatial (100 km) variations in these traits after (i) translocating 576 plants across a span from the southern Appalachian Mountains in NC, USA, to the Piedmont, GA, USA, which includes north- and south-facing slope habitats and (ii) the experimental manipulation of diffuse light and soil moisture.Important findings We find that when translocated into a novel habitats, with novel environmental conditions that often are more extreme than the source habitat, both species appear capable of considerable morphological acclimation and generally converge to similar trait values. Hepatica nobilis does not exhibit mean trait values particularly different from those of A. arifolium, but it demonstrates much greater phenotypic plasticity. These results indicate that relatively conservative plant species nonetheless acclimate and survive across heterogeneous environmental conditions.     

利用RAPD技术进行植物性状标记及辅助选择

近等基因系、混合分离群体法是ＲＡＰＤ 标记的主要策略。目前,ＲＡＰＤ标记广泛用于抗线虫、抗病、雄性不育等辅助选择的研究中,取得了可喜的成绩。由于遗传距离的不同,使ＲＡＰＤ 标记具有基因型的差异。寻找无重组的ＲＡＰＤ 标记或将ＲＡＰＤ标记转化为ＲＦＬＰ标记,可以解决这一问题。随着连锁程度的降低选择效率也随着降低。相斥相的ＲＡＰＤ标注可提高选择效率将ＲＡＰＤ标记转化为ＳＣＡＲｓ、ＡＰＳＰｓ 标记,可以解决ＲＡＰＤ 标记稳定性差的问题。来源于ＲＡＰＤ 标记的ＳＣＡＲｓ 标记将在辅助选择中发挥巨大的作用。     

Trait means,trait plasticity and trait differences to other species jointly explain species performances in grasslands of varying diversity

Functional traits may help to explain the great variety of species performances in plant communities, but it is not clear whether the magnitude of trait values of a focal species or trait differences to co‐occurring species are key for trait‐based predictions. In addition, trait expression within species is often plastic, but this variation has been widely neglected in trait‐based analyses. We studied functional traits and plant biomass of 59 species in 66 experimental grassland mixtures of varying species richness (Jena Experiment). We related mean species performances (species biomass and relative yield RY) and their plasticities along the diversity gradient to trait‐based pedictors involving mean species traits (T_mean), trait plasticities along the diversity gradient (T_slope), extents of trait variation across communities (T_CV; coefficient of variation) and hierarchical differences (T_diff) and trait distances (absolute values of trait differences T_dist) between focal and co‐occurring species. T_mean (30–55%) and T_diff (30–33%) explained most variation in mean species performances and their plasticities, but T_slope (20–25%) was also important in explaining mean species performances. The mean species traits and the trait differences between focal species and neighbors with the greatest explanatory power were related to plant size and stature (shoot length, mass:height ratios) and leaf photosynthetic capacity (specific leaf area, stable carbon isotopes and leaf nitrogen concentration). The contribution of trait plasticities in explaining species performances varied in direction (positive or negative) and involved traits related to photosynthetic capacity, nitrogen acquisition (nitrogen concentrations and stable isotopes) as well as structural stability (shoot carbon concentrations). Our results suggest that incorporating plasticity in trait expression as well as trait differences to co‐occurring species is critical for extending trait‐based analyses to understand the assembly of plant communities and the contribution of individual species in structuring plant communities.     

Isolation of primers for candidate genes for mechano-sensing in five Neotropical tree species

Mechanical signals have an impact on plant development. Tropical rainforest trees display large variability for life–history traits related to biomechanics and therefore are a unique study system to better understand biomechanical trait variability from an evolutionary perspective. From sequences and gene expression data available in model species, we developed specific primers for six candidate genes for mechano-sensing in five tropical species. Most of the gene sequences were polymorphic in most species.     

The candidate gene approach in plant genetics: a review

The candidate gene (CG) approach has been applied in plant genetics in the past decade for the characterisation and cloning of Mendelian and quantitative trait loci (QTLs). It constitutes a complementary strategy to map-based cloning and insertional mutagenesis. The goal of this paper is to present an overview of CG analyses in plant genetics. CG analysis is based on the hypothesis that known-function genes (the candidate genes) could correspond to loci controlling traits of interest. CGs refer either to cloned genes presumed to affect a given trait (`functional CGs') or to genes suggested by their close proximity on linkage maps to loci controlling the trait (`positional CGs'). In plant genetics, the most common way to identify a CG is to look for map co-segregation between CGs and loci affecting the trait. Statistical association analyses between molecular polymorphisms of the CG and variation in the trait of interest have also been carried out in a few studies. The final validation of a CG will be provided through physiological analyses, genetic transformation and/or sexual complementation. Theoretical and practical applications of validated CGs in plant genetics and breeding are discussed.     

GOOD GENES AND DIRECT SELECTION IN THE EVOLUTION OF MATING PREFERENCES

A model is used to study quantitatively the impact of a good genes process and direct natural selection on the evolution of a mating preference. The expression of a male display trait is proportional to genetic quality, which is determined by the number of deleterious mutations a male carries throughout his genome. Genetic variances and covariances, including the covariance between the preference and male trait that drives the good genes process, are allowed to evolve under an infinitesimal model. Results suggest that the good genes process generates only weak indirect selection on preferences, with an effective selection intensity of a few percent or less. If preferences are subject to direct natural selection of the intensity observed for other characters, the good genes process alone is not expected to exaggerate the male trait by more than a few phenotypic standard deviations, contrary to what is observed in highly sexually selected species. Good genes can, however, cause substantial exaggeration if preference genes are nearly selectively neutral. Alternatively, direct selection on preference genes, acting on mating behavior itself or on the genes' pleiotropic effects, can cause mating preferences and male display traits to be exaggerated by any degree. Direct selection of preference genes may therefore play an important role in species that show extreme sexual selection.