Summary: Black poplar (Populus nigra) is a potential feedstock for cellulosic ethanol production, although breeding for this specific end use is required. Our goal was to identify associations between single nucleotide polymorphism (SNP) markers within candidate genes encoding cellulose and lignin biosynthetic enzymes, with chemical wood property phenotypic traits, toward the aim of developing genomics‐based breeding technologies for bioethanol production. Pyrolysis molecular beam mass spectrometry was used to determine contents of five‐ and six‐carbon sugars, lignin, and syringyl : guaiacyl ratio. The association population included 599 clones from 17 half‐sib families, which were successfully genotyped using 433 SNPs from 39 candidate genes. Statistical analyses were performed to estimate genetic parameters, linkage disequilibrium (LD), and single marker and haplotype‐based associations. A moderate to high heritability was observed for all traits. The LD, across all candidate genes, showed a rapid decay with physical distance. Analysis of single marker–phenotype associations identified six significant marker–trait pairs, whereas nearly 280 haplotypes were associated with phenotypic traits, in both an individual and multiple trait‐specific manner. The rapid decay of LD within candidate genes in this population and the genetic associations identified suggest a close relationship between the associated SNPs and the causative polymorphisms underlying the genetic variation of lignocellulosic traits in black poplar.

The genetic and physiological mechanisms underlying the relationship between water-soluble carbohydrates (WSC) and water stress tolerance are scarcely known. This study aimed to evaluate the main WSC in stems, and the expression of genes involved in fructan metabolism in wheat genotypes growing in a glasshouse with water stress (WS; 50% field capacity from heading) and full irrigation (FI; 100% field capacity). Eight wheat genotypes (five tolerant and three susceptible to water stress) were evaluated initially (experiment 1) and the two most contrasting genotypes in terms of WSC accumulation were evaluated in a subsequent experiment (experiment 2). Maximum accumulation of WSC occurred 10–20 days after anthesis. Under WS, the stress-tolerant genotype exhibited higher concentrations of WSC, glucose, fructose and fructan in the stems, compared to FI. In addition, the stress-tolerant genotype exhibited higher up-regulation of the fructan 1-fructosyltransferase B (1-FFTB) and fructan 1-exohydrolase w2 (1-FEHw2) genes, whereas the susceptible cultivar presented an up-regulation of the fructan 6-fructosyltransferase (6-SFT) and fructan 1-exohydrolase w3 (1-FEHw3) genes. Our results indicated clear differences in the pattern of WSC accumulation and the expression of genes regulating fructan metabolism between the tolerant and susceptible genotypes under WS.

Aquaporins (AQPs) are transmembrane proteins essential for controlling the flow of water and other molecules required for development and stress tolerance in plants, including important crop species such as wheat (Triticum aestivum). In this study, we utilized a genomic approach for analyzing the information about AQPs available in public databases to characterize their structure and function. Furthermore, we validated the expression of a suite of AQP genes, at the transcriptional level, including accessions with contrasting responses to drought, different organs and water stress levels. We found 65 new AQP genes, from which 60% are copies expanded by polyploidization. Sequence analysis of the AQP genes showed that the purifying selection pressure acted on duplicate genes, which was related to a high conservation of the functions. This situation contrasted with the expression patterns observed for different organs, developmental stages or genotypes under water deficit conditions, which indicated functional divergence at transcription. Expression analyses on contrasting genotypes showed high gene transcription from Tonoplast Intrinsic Protein 1 (TIP1) and 2 (TIP2), and Plasma Membrane Intrinsic Protein 1 (PIP1) and 2 (PIP2) subfamilies in roots and from TIP1 and PIP1 subfamilies in leaves. Interestingly, during severe drought stress, 4 TIP genes analyzed in leaves of the tolerant accession reached up to 15-fold the level observed at the susceptible genotype, suggesting a positive relationship with drought tolerance. The obtained results extend our understanding of the structure and function of AQPs, particularly under water stress conditions.

International audienceThe main objective of this study was to describe trends in genetic parameters for wood density and radial growth through cambial age in a radiata pine progeny test established in the south of Chile. Wood samples from 31 half-sib families of radiata pine were obtained and submitted to an X-ray densitometry procedure. The analyzed traits were total ring width (TRW), ring area (RA), and average ring density (ARD). Statistical analyses were conducted to estimate the heritability of individual traits at the ring level and the ring-to-ring genetic correlation between ARD and radial growth. The pattern of change of genetic parameters with cambial age is especially affected between rings 6 to 10, which can be related with the transition from juvenile wood to adult wood. The genetic control of ring density was strong at cambial ages 2 and 3 and dropped to zero within the transition zone (rings 6 and 8). After ring 10, the genetic control of ARD varied from low to moderate. From cambial ages 3 to 9, the genetic correlation between ring density and radial growth was positive. From rings 5 to 9, the phenotypic correlation was also positive but low. At rings 8 and 9, the relationship between radial growth and density changed and strong within-plot competition effects possibly affected the phenotypic correlation between ring density and radial growth. After ring 9, the genetic correlation was negative but weak. The phenotypic correlation between ring density and radial growth increased its negative magnitude towards cambial age 14, which may have been the result of local micro site influences, such as competition for light and nutrients.Contrôle génétique de la densité et de la croissance radiale en fonction de l'âge cambial dans un test de familles de pin radiata. L'objectif de cette analyse est d'évaluer le contrôle génétique de la densité du cerne en fonction de l'âge cambial, et d'estimer les corrélations génétiques entre croissance radiale et densité du bois, en fonction également de l'âge cambial, chez le pin radiata au Chili. Des échantillons de bois provenant de 31 familles de demi-frères de pin radiata installées dans un test de descendances maternelles installé au Chili ont été récoltés et soumis à une procédure d'analyse microdensitométrique aux rayons X. Les caractères analysés sont la largeur de cerne (TRW), la surface du cerne (RA) et la densité moyenne du cerne (ARD). Des analyses statistiques ont permis d'estimer l'héritabilité de ces caractères au niveau du cerne, ainsi que les corrélations génétiques entre caractères de croissance radiale et densité du cerne en fonction de l'âge cambial. La tendance générale de l'évolution des paramètres génétiques change particulièrement au niveau des cernes 6 à 10 depuis la moelle, ce qui reflète peut-être le passage du bois juvénile au bois adulte. Le contrôle génétique de la densité du cerne est élevé aux âges cambiaux 2 et 3, et tombe à 0 au niveau des cernes 6 à 8. Après le cerne 10, le contrôle génétique de la densité du cerne devient faible à modéré. De l'âge cambial 3 à l'âge cambial 9, la corrélation génétique entre la densité du cerne et la croissance radiale est positive. Entre les cernes 5 et 9, la corrélation phénotypique entre les mêmes caractères est également positive, mais faible. Au niveau des cernes 8 et 9, la relation entre la densité et la croissance radiale change et la corrélation phénotypique entre la densité du cerne et la croissance radiale est alors probablement affectée par de forts effets compétition à l'intérieur des placeaux. Après le cerne 9, la corrélation génétique devient négative mais reste faible. Par contre, la corrélation phénotypique négative entre densité du cerne et croissance radiale devient plus intense jusqu'à culminer à l'âge cambial 14. L'ampleur de cette corrélation phénotypique est peut-être dominée par des effets microsite du type compétition pour la lumière et pour les éléments minéraux

Background: Populus trichocarpais an important forest tree species for the generation of lignocellulosic ethanol. Understanding the genomic basis of biomass production and chemical composition of wood is fundamental in supporting genetic improvement programs. Considerable variation has been observed in this species for complex traits related to growth, phenology, ecophysiology and wood chemistry. Those traits are influenced by both polygenic control and environmental effects, and their genome architecture and regulation are only partially understood. Genome wide association studies (GWAS) represent an approach to advance that aim using thousands of single nucleotide polymorphisms (SNPs). Genotyping using exome capture methodologies represent an efficient approach to identify specific functional regions of genomes underlying phenotypic variation.Results: We identified 813 K SNPs, which were utilized for genotyping 461P. trichocarpaclones, representing 101 provenances collected from Oregon and Washington, and established in California. A GWAS performed on 20 traits, considering single SNP-marker tests identified a variable number of significant SNPs (p-value < 6.1479E-8) in association with diameter, height, leaf carbon and nitrogen contents, and δ¹⁵N. The number of significant SNPs ranged from 2 to 220 per trait. Additionally, multiple-marker analyses by sliding-windows tests detected between 6 and 192 significant windows for the analyzed traits. The significant SNPs resided within genes that encode proteins belonging to different functional classes as such protein synthesis, energy/metabolism and DNA/RNA metabolism, among others.Conclusions: SNP-markers within genes associated with traits of importance for biomass production were detected. They contribute to characterize the genomic architecture ofP. trichocarpabiomass required to support the development and application of marker breeding technologies.