Marc Villar

Productivity, water-use efficiency and tolerance to moderate water deficit correlate in 33 poplar genotypes from a Populus deltoides × Populus trichocarpa F1 progeny

Genotypic variability for productivity, water-use efficiency and leaf traits in 33 genotypes selected from an F1 progeny of Populus deltoides Bartr. ex Marsh x Populus trichocarpa L. was explored under optimal and moderate water-deficit conditions. Saplings of the 33 genotypes were grown in a two-plot open field at INRA Orléans (France) and coppiced every year. A moderate water deficit was induced during two successive years on one plot by withholding irrigation, while the second one remained irrigated (control). Stem biomass and leaf structure (e.g., specific leaf area and leaf area) were measured in 2004 and 2005 and functional leaf traits (e.g., carbon isotope discrimination, Delta) were measured only in 2004. Tolerance to water deficit was estimated at genotype level as the ability to limit losses in biomass production in water deficit versus control trees. Stem biomass, leaf structure and Delta displayed a significant genotypic variability whatever the irrigation regime. For all traits, genotype ranks remained stable across years for similar irrigation conditions. Carbon isotope discrimination scaled negatively with productivity and leaf nitrogen content in controls. The most productive genotypes were the least tolerant to moderate water deficit. No relationship was evidenced between Delta and the level of tolerance to water deficit. The relationships between traits evidenced in this collection of P. deltoides x P. trichocarpa F1 genotypes contrast with the ones that were previously detected in a collection of P. deltoides x Populus nigra L. cultivars tested in the same field trial.

A Single Gene Cluster Controls Incompatibility and Partial Resistance to Various Melampsora larici-populina Races in Hybrid Poplars.

ABSTRACT Complete cosegregation for race-specific incompatibility with three Melampsora larici-populina rust races was observed in five F(1) hybrid progenies of Populus, with different patterns among the various progenies. A single gene cluster could explain these segregations: one locus with multiple alleles or two tightly linked loci controlling complete resistance to E1 and E3, and two tightly linked loci for E2. The random amplified polymorphic DNA marker OPM03/04_480 was linked to that cluster in all families (<1 cM). This marker accounted for more than 70% of the genetic variation for field resistance in each family (heritability approximately 0.40). The same marker accounted for up to 64% of the clonal variation for growth in the nursery under natural inoculum pressure; the weak tolerance to rust of F(1) interspecific hybrids was attributed to a genetic background effect. Partial resistance was split into epidemiological components (heritability ranged from 0.35 to 0.87). Genotypic correlations among resistance traits for the different races were high (0.73 to 0.90). However, correlations among different resistance components for a single race were not all significant. A major quantitative trait locus for all components of partial resistance to E2 was associated to the cluster controlling incompatibility to E1 and E3 and marked by OPM03/04_480 (R(2)from 48 to 68%).

Genetic analysis of phenotypic variation for ectomycorrhiza formation in an interspecific F1 poplar full-sib family

AbstractA plant’s capability to develop ectomycorrhizal symbiosis is under the control of both genetic and environmental factors. In order to determine the roles played by these different factors, we have performed a quantitative genetic analysis of the ability of poplar trees to form ectomycorrhizas. Quantitative genetics were applied to an interspecific family of poplar for which the two parental genetic maps had already been described, and for which data analyses concerning fungal aggressors were obtained. Quantitative trait loci (QTL) related to ectomycorrhiza formation were identified and located in the genetic maps of the two parents. One QTL was located at a linkage group of the genetic map of Populus trichocarpa showing a high concentration of several QTL involved in the pathogenic interaction with the fungus Melampsora larici-populina, the causal agent of leaf rust.

Variation in the ability to form ectomycorrhizas in the F1 progeny of an interspecific poplar (Populus spp.) cross

Abstract The aim of this study was to determine the existence of a genetic basis for the ability to form ectomycorrhiza on a model angiosperm tree (Populus, poplar). Parental clones and 18 progeny from a controlled interspecific cross between Populus deltoides and Po- pulus trichocarpa were grown in a glasshouse and inoculated with mycelium of the ectomycorrhizal fungus Laccaria bicolor. Three months after inoculation, the percentage of mycorrhizal root tips was determined for each inoculated plant. The data indicate variability in the ability to form ectomycorrhizas among the F1 progeny, including individual progeny which are different to either parent. This suggests a genetic basis for mycorrhiza formation.

Integrating genome annotation and QTL position to identify candidate genes for productivity, architecture and water-use efficiency in Populus spp

BackgroundHybrid poplars species are candidates for biomass production but breeding efforts are needed to combine productivity and water use efficiency in improved cultivars. The understanding of the genetic architecture of growth in poplar by a Quantitative Trait Loci (QTL) approach can help us to elucidate the molecular basis of such integrative traits but identifying candidate genes underlying these QTLs remains difficult. Nevertheless, the increase of genomic information together with the accessibility to a reference genome sequence (Populus trichocarpa Nisqually-1) allow to bridge QTL information on genetic maps and physical location of candidate genes on the genome. The objective of the study is to identify QTLs controlling productivity, architecture and leaf traits in a P. deltoides x P. trichocarpa F1 progeny and to identify candidate genes underlying QTLs based on the anchoring of genetic maps on the genome and the gene ontology information linked to genome annotation. The strategy to explore genome annotation was to use Gene Ontology enrichment tools to test if some functional categories are statistically over-represented in QTL regions.ResultsFour leaf traits and 7 growth traits were measured on 330 F1 P. deltoides x P. trichocarpa progeny. A total of 77 QTLs controlling 11 traits were identified explaining from 1.8 to 17.2% of the variation of traits. For 58 QTLs, confidence intervals could be projected on the genome. An extended functional annotation was built based on data retrieved from the plant genome database Phytozome and from an inference of function using homology between Populus and the model plant Arabidopsis. Genes located within QTL confidence intervals were retrieved and enrichments in gene ontology (GO) terms were determined using different methods. Significant enrichments were found for all traits. Particularly relevant biological processes GO terms were identified for QTLs controlling number of sylleptic branches: intervals were enriched in GO terms of biological process like ‘ripening’ and ‘adventitious roots development’.ConclusionBeyond the simple identification of QTLs, this study is the first to use a global approach of GO terms enrichment analysis to fully explore gene function under QTLs confidence intervals in plants. This global approach may lead to identification of new candidate genes for traits of interest.

Variations in bulk leaf carbon isotope discrimination, growth and related leaf traits among three Populus nigra L. populations

The ongoing global change could be an additional threat to the establishment and the long-term survival of Populus nigra L., an emblematic European riparian species. With the general aim of gaining insights into the adaptive potential of this species, we (i) quantified variations within and among three French P. nigra populations for key physiological attributes, i.e., water-use efficiency (assessed from bulk leaf carbon isotope discrimination, Δ(13)C), growth performance and related leaf traits, (ii) examined genotype and population by environment interactions, and (iii) explored the relationship between Δ(13)C and growth. Thirty genotypes were sampled in each of three naturally established populations and grown in two different sites, Orléans (ORL) and Guémené-Penfao (GMN). In ORL, two similar plots were established and different watering regimes were applied in order to test for the drought response. Significant variations were observed for all traits within and among populations irrespective of site and watering. Trait variation was larger within than among populations. The effect of drought was neither genotype- nor population-dependent, contrary to the effect of site. The population ranking was maintained in all sites and watering regimes for the two most complex traits: Δ(13)C and growth. Moreover, these two traits were unrelated, which indicates that (i) water-use efficiency and growth are largely uncoupled in this species, and (ii) the environmental factors driving genetic structuration for Δ(13)C and growth act independently. The large variations found within populations combined with the consistent differences among populations suggest a large adaptive potential for P. nigra.

Genetic variation in productivity, leaf traits and carbon isotope discrimination in hybrid poplars cultivated on contrasting sites

Abstract• We examined the relationships between productivity, leaf traits and carbon isotope discrimination in bulk leaf matter (Δ1) and in phloem sap (Δs) from more than 5-year-old trees belonging to Populus deltoides × P. nigra and Populus trichocarpa × P. deltoides; trees were grown in alluvial and non alluvial sites in a commercial poplar plantation.• On both sites, a large genetic variability was evidenced for all variables. The genotypic ranking remained stable between years for all variables, while it differed between sites. Δ1 scaled positively with Δs and neither Δ1 nor Δs were correlated with productivity. A significant genotype by site interaction was evident for all variables. The non alluvial site resulted in lower productivity, and in thicker/denser leaves with lower nitrogen and carbon contents. Noteworthy, the genotypic ranking for Δ1 measured at the alluvial site was similar to that previously established in a glasshouse.• As observed in previous studies from younger trees, there is a potential to select genotypes, combining high productivity and high water-use efficiency, for growth in moderately drought-prone areas.Résumé• La productivité, des caractères foliaires et la discrimination isotopique vis-à-vis du carbone de la matière organique des feuilles (Δ1) et de la sève élaborée (Δs) ont été étudiés chez Populus deltoides × P. nigra et Populus trichocarpa × P. deltoides à partir d’arbres âgés de plus de cinq ans, cultivés en peupleraie sur des sites alluviaux et non alluviaux.• Des différences génotypiques ont été observées pour toutes les variables. Le classement des génotypes était conservé entre deux années, alors qu’il variait entre sites une année donnée. Δ1 était corrélé positivement avec Δs et aucun lien n’a été détecté entre Δ1 ou Δs et productivité. Une interaction significative entre génotype et site a été observée pour toutes les variables. Les arbres du site non alluvial se caractérisaient par une plus faible productivité et des feuilles plus épaisses/denses avec des teneurs en azote et en carbone plus faibles. De façon intéressante, le classement des génotypes pour Δ1 était maintenu entre les expériences réalisées sur site alluvial et celles précédemment menées en serre.• Toutes expériences confondues, il semble possible de sélectionner des génotypes productifs et efficients afin d’étendre les plantations à des terrains enclins à des sécheresses modérées.

Expression analysis of LIM gene family in poplar, toward an updated phylogenetic classification.

BackgroundPlant LIM domain proteins may act as transcriptional activators of lignin biosynthesis and/or as actin binding and bundling proteins. Plant LIM genes have evolved in phylogenetic subgroups differing in their expression profiles: in the whole plant or specifically in pollen. However, several poplar PtLIM genes belong to uncharacterized monophyletic subgroups and the expression patterns of the LIM gene family in a woody plant have not been studied.FindingsIn this work, the expression pattern of the twelve duplicated poplar PtLIM genes has been investigated by semi quantitative RT-PCR in different vegetative and reproductive tissues. As in other plant species, poplar PtLIM genes were widely expressed in the tree or in particular tissues. Especially, PtXLIM1a, PtXLIM1b and PtWLIM1b genes were preferentially expressed in the secondary xylem, suggesting a specific function in wood formation. Moreover, the expression of these genes and of the PtPLIM2a gene was increased in tension wood. Western-blot analysis confirmed the preferential expression of PtXLIM1a protein during xylem differentiation and tension wood formation. Genes classified within the pollen specific PLIM2 and PLIM2-like subgroups were all strongly expressed in pollen but also in cottony hairs. Interestingly, pairs of duplicated PtLIM genes exhibited different expression patterns indicating subfunctionalisations in specific tissues.ConclusionsThe strong expression of several LIM genes in cottony hairs and germinating pollen, as well as in xylem fibers suggests an involvement of plant LIM domain proteins in the control of cell expansion. Comparisons of expression profiles of poplar LIM genes with the published functions of closely related plant LIM genes suggest conserved functions in the areas of lignin biosynthesis, pollen tube growth and mechanical stress response. Based on these results, we propose a novel nomenclature of poplar LIM domain proteins.

Is the ranking of poplar genotypes for leaf carbon isotope discrimination stable across sites and years in two different full-sib families?

Introduction Because of its vigorous growth, poplar can play an important role for sustainable production of woody biomass to cover renewable energy needs. Hence, the selection of suitable genotypes has to be based on relevant traits, among which intrinsic water use efficiency (Wi, estimated through leaf carbon isotope discrimination, Δ) may be a key trait. Besides a large genetic variation in Δ among the frequently planted poplar hybrids, the use of Δ in deployment or breeding programmes requires insights in the robustness of the genotype ranking for Δ across environments and years.Methods Two F1 full-sib families of poplar (Populus deltoides × Populus nigra and Populus deltoides × Populus trichocarpa) were grown at two sites in Europe, i.e. northern Italy and central France. For each family, leaf samples from 31 F1 genotypes collected during different field studies were used (1) to assess the effect of genotype, site and year on Δ in leaves, as well as their mutual interactions, and (2) to elucidate the relationships between Δ, leaf morphology and tree dimensions.Results Under the well-watered conditions of our study, a low to moderate genetic variability was observed in the two poplar families. Within-family broad-sense heritability values ranged from 0 to 0.49. The ranking of genotypes for Δ was more stable between years than between sites.Conclusions The study confirmed the occurrence of some degree of genetic variability of Δ in the studied poplar families and the possibility to identify genotypes with low, stable Δ values across years. However, the significant genotype-by-site interactions in our study suggest that selection for larger water use efficiency or lower Δ in these families has to consider specific responses in different environments.

With a little help from my friends: hybrid fertility of exotic Populus x canadensis enhanced by related native Populus nigra

Hybridization and genetic swamping by planted exotic Populus taxa are putative threats for native Populus resources. We investigated the potential for hybridization between the exotic hybrid Populus x canadensis Moench and its wild relative, the European black poplar (Populus nigra L.), by a series of pollination experiments in the greenhouse. We also tested the effect of mixtures of pollen from the taxon’s own pollen and pollen of the foreign taxon on mating success in reciprocal crosses. We observed reduced pollen and seed viability of the hybrid clones of P. x canadensis compared to the clones of the parental species P. nigra. Surprisingly, when in combination with pollen of its wild relative P. nigra, pollen of exotic P. x canadensis sired significantly better on its own flowers. In poplar breeding, the pollen mentor technique which uses pollen mixes of artificially inactivated conspecific pollen and untreated incompatible foreign pollen, has been successfully used to overcome incompatibility barriers. The results of this study suggest that in the wild, where mixed pollen loads are common, similar effects as the pollen mentor effects may enhance the invasiveness of exotic P. x canadensis. This study helps to explain former field observations and contributes to the understanding of potential environmental impacts of commercial exotic and transgene poplar plantations.