Plántulas de Populus alba pretratadas con endófitos muestran una mayor tolerancia a Venturia tremulae

Algunos hongos endófitos parecen modular la respuesta de las plantas ante ataques de ciertos patógenos o insectos. En este trabajo se estudió la implicación de hongos endófitos de Populus alba en la tolerancia al patógeno necrotrofo Venturia tremulae, causante de la muerte de ramillos en especies de la sección Populus, siendo P. alba más tolerante que otras especies de la sección. Se evaluó in vitro el efecto de doce cepas de endófitos enfrentándolas al patógeno con el fin de seleccionar aquellas con mayor potencial de biocontrol. Se seleccionaron diez endófitos que fueron inoculados mediante solución esporal de una mezcla de todos ellos, de forma preventiva sobre plántulas de una savia de P. alba. Transcurridos 15 días, se inoculó al patógeno. Aunque en general los síntomas mostrados por las plantas fueron bajos, la mezcla de endófitos redujo la incidencia y severidad de los síntomas causados por el patógeno. Los resultados sugieren que los endófitos de P. alba limitarían los síntomas causados por el patógeno en este hospedante

Causes and consequences of large clonal assemblies in a poplar hybrid zone.

Asexual reproduction is a common and fundamental mode of reproduction in plants. Although persistence in adverse conditions underlies most known cases of clonal dominance, proximal genetic drivers remain unclear, in particular for populations dominated by a few large clones. In this paper, we studied a clonal population of the riparian tree Populus alba in the Douro river basin (northwestern Iberian Peninsula) where it hybridizes with P. tremula, a species that grows in highly contrasted ecological conditions. We used 73 nuclear microsatellites to test whether genomic background (species ancestry) is a relevant cause of clonal success, and to assess the evolutionary consequences of clonal dominance by a few genets. Additional Genotyping-by-Sequencing (GBS) data were produced to estimate the age of the largest clones. We found that a few ancient (over a few thousand years old) and widespread genets dominate the population, both in terms of clone size and number of sexual offspring produced. Interestingly, large clones possessed two genomic regions introgressed from P. tremula, which may have favored their spread under stressful environmental conditions. At the population level, the spread of large genets was accompanied by an overall ancient (>0.1 Myr) but soft decline of effective population size. Despite this decrease, and the high clonality and dominance of sexual reproduction by large clones, the Douro hybrid zone still displays considerable genetic diversity and low inbreeding. This suggests that, even in extreme cases as in the Douro, asexual and sexual dominance of a few large, geographically-extended individuals does not threaten population survival. This article is protected by copyright. All rights reserved

Plántulas de Populus alba pretratadas con endófitos muestran una mayor tolerancia a Venturia tremulae

Algunos hongos endófitos parecen modular la respuesta de las plantas ante ataques de ciertos patógenos o insectos. En este trabajo se estudió la implicación de hongos endófitos de Populus alba en la tolerancia al patógeno necrotrofo Venturia tremulae, causante de la muerte de ramillos en especies de la sección Populus, siendo P. alba más tolerante que otras especies de la sección. Se evaluó in vitro el efecto de doce cepas de endófitos enfrentándolas al patógeno con el fin de seleccionar aquellas con mayor potencial de biocontrol. Se seleccionaron diez endófitos que fueron inoculados mediante solución esporal de una mezcla de todos ellos, de forma preventiva sobre plántulas de una savia de P. alba. Transcurridos 15 días, se inoculó al patógeno. Aunque en general los síntomas mostrados por las plantas fueron bajos, la mezcla de endófitos redujo la incidencia y severidad de los síntomas causados por el patógeno. Los resultados sugieren que los endófitos de P. alba limitarían los síntomas causados por el patógeno en este hospedante

Agronomic performance of Populus deltoides trees engineered for biofuel production

Background: One of the major barriers to the development of lignocellulosic feedstocks is the recalcitrance of plant cell walls to deconstruction and saccharifcation. Recalcitrance can be reduced by targeting genes involved in cell wall biosynthesis, but this can have unintended consequences that compromise the agronomic performance of the trees under feld conditions. Here we report the results of a feld trial of fourteen distinct transgenic Populus deltoides lines that had previously demonstrated reduced recalcitrance without yield penalties under greenhouse conditions. Results: Survival and productivity of the trial were excellent in the frst year, and there was little evidence for reduced performance of the transgenic lines with modifed target gene expression. Surprisingly, the most striking phenotypic efects in this trial were for two empty-vector control lines that had modifed bud set and bud fush. This is most likely due to somaclonal variation or insertional mutagenesis. Traits related to yield, crown architecture, herbivory, patho‑ gen response, and frost damage showed few signifcant diferences between target gene transgenics and empty vector controls. However, there were a few interesting exceptions. Lines overexpressing the DUF231 gene, a putative O-acetyltransferase, showed early bud fush and marginally increased height growth. Lines overexpressing the DUF266 gene, a putative glycosyltransferase, had signifcantly decreased stem internode length and slightly higher volume index. Finally, lines overexpressing the PFD2 gene, a putative member of the prefoldin complex, had a slightly reduced volume index. Conclusions: This feld trial demonstrates that these cell wall modifcations, which decreased cell wall recalcitrance under laboratory conditions, did not seriously compromise frst-year performance in the feld, despite substantial challenges, including an outbreak of a stem boring insect (Gypsonoma haimbachiana), attack by a leaf rust pathogen (Melampsora spp.), and a late frost event. This bodes well for the potential utility of these lines as advanced biofuels feedstocks

The Atlantic-Mediterranean watershed, river basins and glacial history shape the genetic structure of Iberian poplars

Recent phylogeographic studies have elucidated the effects of Pleistocene glaciations and of Pre-Pleistocene events on populations from glacial refuge areas. This study investigates those effects in riparian trees (Populus spp.), whose particular features may convey enhanced resistance to climate fluctuations. We analysed the phylogeographic structure of 44 white (Populus alba), 13 black (Populus nigra) and two grey (Populus x canescens) poplar populations in the Iberian Peninsula using plastid DNA microsatellites and sequences. We also assessed fine-scale spatial genetic structure and the extent of clonality in four white and one grey poplar populations using nuclear microsatellites and we determined quantitative genetic differentiation (Q ST) for growth traits in white poplar. Black poplar displayed higher regional diversity and lower differentiation than white poplar, reflecting its higher cold-tolerance. The dependence of white poplar on phreatic water was evidenced by strong differentiation between the Atlantic and Mediterranean drainage basins and among river basins, and by weaker isolation by distance within than among river basins. Our results suggest confinement to the lower river courses during glacial periods and moderate interglacial gene exchange along coastlines. In northern Iberian river basins, white poplar had lower diversity, fewer private haplotypes and larger clonal assemblies than in southern basins, indicating a stronger effect of glaciations in the north. Despite strong genetic structure and frequent asexual propagation in white poplar, some growth traits displayed adaptive divergence between drainage and river basins (Q ST > F ST), highlighting the remarkable capacity of riparian tree populations to adapt to regional environmental conditions. © 2012 Blackwell Publishing Ltd

Diversidad de hongos endófitos en especies forestales y su posible papel en la defensa de su hospedante y la degradación de la madera

Los hongos endófitos juegan un papel decisivo en diferentes procesos biológicos. Se consideran implicados en la resistencia de las plantas ante diferentes tipos de estrés. Además, ante la senescencia de los tejidos que habitan, parecen ejercer un papel relevante en las fases iniciales de degradación. Con el fin de progresar en el conocimiento de sus funciones ecológicas se estudió, mediante herramientas metagenómicas, la flora endófita asociada a dos especies forestales, Ulmus minor y Eucalyptus globulus, y su implicación en la defensa de la planta ante la grafiosis y en la degradación de la madera, respectivamente. En el olmo se detectaron 164 unidades taxonómicas operacionales (OTUs) y la frecuencia de dos órdenes fúngicos se correlacionó positivamente con la resistencia de su hospedante a la grafiosis. En ramillos de eucalipto en diferentes fases de degradación se detectaron 115 OTUs, los cuales parecen actuar de forma secuencial en el proceso de acuerdo a su taxonomía y capacidad de degradación de los diferentes componentes de la madera. Los resultados sitúan a los endófitos como herramientas biotecnológicas potenciales en el control de enfermedades y la industria de la celulosa

Admixture mapping of quantitative traits in Populus hybrid zones: power and limitations

Uncovering the genetic architecture of species differences is of central importance for understanding the origin and maintenance of biological diversity. Admixture mapping can be used to identify the number and effect sizes of genes that contribute to the divergence of ecologically important traits, even in taxa that are not amenable to laboratory crosses because of their long generation time or other limitations. Here, we apply admixture mapping to naturally occurring hybrids between two ecologically divergent Populus species. We map quantitative trait loci for eight leaf morphological traits using 77 mapped microsatellite markers from all 19 chromosomes of Populus. We apply multivariate linear regression analysis allowing the modeling of additive and non-additive gene action and identify several candidate genomic regions associated with leaf morphology using an information-theoretic approach. We perform simulation studies to assess the power and limitations of admixture mapping of quantitative traits in natural hybrid populations for a variety of genetic architectures and modes of gene action. Our results indicate that (1) admixture mapping has considerable power to identify the genetic architecture of species differences if sample sizes and marker densities are sufficiently high, (2) modeling of non-additive gene action can help to elucidate the discrepancy between genotype and phenotype sometimes seen in interspecific hybrids, and (3) the genetic architecture of leaf morphological traits in the studied Populus species involves complementary and overdominant gene action, providing the basis for rapid adaptation of these ecologically important forest trees