Developmental and Environmental Regulation of Aquaporin Gene Expression across Populus Species: Divergence or Redundancy?

Aquaporins (AQPs) are membrane channels belonging to the major intrinsic proteins family and are known for their ability to facilitate water movement. While in Populus trichocarpa, AQP proteins form a large family encompassing fifty-five genes, most of the experimental work focused on a few genes or subfamilies. The current work was undertaken to develop a comprehensive picture of the whole AQP gene family in Populus species by delineating gene expression domain and distinguishing responsiveness to developmental and environmental cues. Since duplication events amplified the poplar AQP family, we addressed the question of expression redundancy between gene duplicates. On these purposes, we carried a meta-analysis of all publicly available Affymetrix experiments. Our in-silico strategy controlled for previously identified biases in cross-species transcriptomics, a necessary step for any comparative transcriptomics based on multispecies design chips. Three poplar AQPs were not supported by any expression data, even in a large collection of situations (abiotic and biotic constraints, temporal oscillations and mutants). The expression of 11 AQPs was never or poorly regulated whatever the wideness of their expression domain and their expression level. Our work highlighted that PtTIP1;4 was the most responsive gene of the AQP family. A high functional divergence between gene duplicates was detected across species and in response to tested cues, except for the root-expressed PtTIP2;3/PtTIP2;4 pair exhibiting 80% convergent responses. Our meta-analysis assessed key features of aquaporin expression which had remained hidden in single experiments, such as expression wideness, response specificity and genotype and environment interactions. By consolidating expression profiles using independent experimental series, we showed that the large expansion of AQP family in poplar was accompanied with a strong divergence of gene expression, even if some cases of functional redundancy could be suspected.

Site index curves for European aspen ( Populus tremula L.) growing on forest land of different soils in Sweden

Summary

Clonal variation in nutrient content in woody biomass of hybrid aspen (Populus tremula L. x P. tremuloides Michx.)

Abstract

Estudi d’adaptació de clons de pollancre (Populus sp.) mitjançant models mitxes en la vall intermèdia de l’Ebre

Durant la dècada dels 80 la DGA (Diputación General de Aragon), va engegar una xarxa d’assaigs experimentals. La major part d’aquests assaigs es troben a la vall de l’Ebre. Padró el 1992 publica les dades de creixement i aporta informació sobre el comportament clonal de cada assaig. Malgrat tot, la enorme desestructura dels assaigs dificultà, en el seu moment, l’anàlisi simultani de les dades. En el treball es proposa un reanàlisi de les dades de la xarxa de la DGA basat en l’ús de models mitxes, amb l’objecte d’interpretar patrons adaptatius i amb especial interès en la descripció de la interacció genotip-ambient. S’utilitzen el models de estabilitat de Shukla, regressions de Finlay-Wilkinson y Eberhart-Russell, AMMI a on el factor ambient és aleatori i el genotip fixe.

Análisis de modelos de perfil del fuste y estudio de la cilindricidad para tres clones de chopo (Populus x euramericana) en Navarra

El presente trabajo tiene por objetivo principal analizar tres funciones de perfil del fuste sobre tres clones de Populus x euramericana (Canadá Blanco, I-214 y MC) en la Comunidad Foral de Navarra para elaborar una tarifa de cubicación con clasificación de volumen. Para minimizar el efecto de la autocorrelación entre los residuos se emplea una estructura de error continua autorregresiva de orden 2 o de orden 3 en función del clon analizado. Por otra parte, se compara el coeficiente local de forma de cada uno de los clones estudiados mediante dos metodologías: el análisis de la varianza de la estimación individual de dicho coeficiente y el contraste del estadístico de máxima verosimilitud entre ajustes, resultando ser el clon Canadá el más cónico de los tres. Los datos utilizados provienen de 143 chopos de plantaciones coetáneas y con mismo marco de plantación (marco real de 4,5 × 4,5 m).

Factors affecting the usability of aspen (Populus tremula) wood dried at different temperature levels

In this dissertation the main aim was to study the usability of aspen wood in the mechanical wood processes, especially the factors that affect the usability of aspen wood, which is dried at different temperature levels. The problematic of varying temperatures from level to another seem to have significant effects on distortions. According to the studies conducted, many practical solutions for drying of aspen timber can be made. European aspen sawn timber should be dried in relatively narrow widths, short lengths, edged and sawn pith free. The results achieved give an interesting view for the distortions of aspen wood between HT drying and heat treatment. The most significant result is that cupping seems to decrease when increasing temperature level from HT drying to heat treatment phase. The difference is significant. Other very obvious result is that bow and crook are increasing between these two temperature levels, bow significantly. Also the modelling gives a good background for this result since cupping is reduced by higher temperatures. It can also be assumed that these distortions can be affected for example by sorting out the timber used to different moisture levels before drying. This could be a very simple solution for practical purposes. From practical point of view, it was also noted during the drying tests performed that the discoloration seem to be no problem for aspen boards dried in temperatures under 150 °C. Altogether, this dissertation covers many interesting points of view of factors affecting distortions of wood in different temperature stages. Aspen as species in use of mechanical wood industries seems to be a species suitable for component production. According to the results, the best yield from aspen timber can be achieved in industry that can utilize relatively short components of sawn wood. Results achieved give a significant indication about the factors affecting distortions of wood at different temperature stages of drying, especially considering European aspen.

Comparison of mechanical properties of tension and opposite wood in Populus

In this paper we focused on the differences of mechanical properties of tension and normal wood of 1-year-old poplar trees, artificially tilted. Elastic and fracture properties have been measured and linked to the anatomy. Tension wood is well known because it prevents good surface finishing and leads to difficulties with sawing. We studied three main mechanical properties: young modulus, energy of cutting and longitudinal residual strain of maturation (with strain gauges) because of their importance in wood technology. Moreover, this work takes place in a larger project of study, the phenomena of axes re-orientation in trees (allowing by the production of reaction wood), where these data are required for biomechanical modelling. The results show that tension wood has a higher young modulus, needs a higher energy to be cut and exhibited a higher level of longitudinal residual strain of maturation than those of normal wood. The results suggest that these differences require deeper analysis of the wood than anatomy: measurement of microfibril orientation in the S2 layer and also the lignin composition in monomeric units.

Long-term acclimation of leaf production, development, longevity and quality following 3 yr exposure to free-air CO2 enrichment during canopy closure in Populus

The effects of elevated CO2 on leaf development in three genotypes of Populus were investigated during canopy closure, following exposure to elevated CO2 over 3 yr using free-air enrichment.• Leaf quality was altered such that nitrogen concentration per unit d. wt (Nmass) declined on average by 22 and 13% for sun and shade leaves, respectively, in elevated CO2. There was little evidence that this was the result of ‘dilution’ following accumulation of nonstructural carbohydrates. Most likely, this was the result of increased leaf thickness. Specific leaf area declined in elevated CO2 on average by 29 and 5% for sun and shade leaves, respectively.• Autumnal senescence was delayed in elevated CO2 with a 10% increase in the number of days at which 50% leaf loss occurred in elevated as compared with ambient CO2.• These data suggest that changes in leaf quality may be predicted following long-term acclimation of fast-growing forest trees to elevated CO2, and that canopy longevity may increase, with important implications for forest productivity.

The transcriptome of Populus in elevated CO2

The consequences of increasing atmospheric carbon dioxide for long-term adaptation of forest ecosystems remain uncertain, with virtually no studies undertaken at the genetic level. A global analysis using cDNA microarrays was conducted following 6 yr exposure of Populus × euramericana (clone I-214) to elevated [CO2] in a FACE (free-air CO2 enrichment) experiment.• Gene expression was sensitive to elevated [CO2] but the response depended on the developmental age of the leaves, and < 50 transcripts differed significantly between different CO2 environments. For young leaves most differentially expressed genes were upregulated in elevated [CO2], while in semimature leaves most were downregulated in elevated [CO2].• For transcripts related only to the small subunit of Rubisco, upregulation in LPI 3 and downregulation in LPI 6 leaves in elevated CO2 was confirmed by anova. Similar patterns of gene expression for young leaves were also confirmed independently across year 3 and year 6 microarray data, and using real-time RT–PCR.• This study provides the first clues to the long-term genetic expression changes that may occur during long-term plant response to elevated CO2.

Elevated atmospheric CO2 and humidity delay leaf fall in Betula pendula, but not in Alnus glutinosa or Populus tremula × tremuloides

Context: Anthropogenic activity has increased the level of atmospheric CO2, which is driving an increase of global temperatures and associated changes in precipitation patterns. At Northern latitudes, one of the likely consequences of global warming is increased precipitation and air humidity. Aims: In this work, the effects of both elevated atmospheric CO2 and increased air humidity on trees commonly growing in northern European forests were assessed. Methods: The work was carried out under field conditions by using Free Air Carbon dioxide Enrichment (FACE) and Free Air Humidity Manipulation (FAHM) systems. Leaf litter fall was measured over 4 years (FACE) or 5 years (FAHM) to determine the effects of FACE and FAHM on leaf phenology. Results: Increasing air humidity delayed leaf litter fall in Betula pendula, but not in Populus tremula × tremuloides. Similarly, under elevated atmospheric CO2, leaf litter fall was delayed in Betula pendula, but not in Alnus glutinosa. Increased CO2 appeared to interact with periods of low precipitation in summer and high ozone levels during these periods to effect leaf fall. Conclusions: This work shows that increased CO2 and humidity delay leaf fall, but this effect is species specific.