Sylleptic Branches Research Articles

Biomass production and characteristics of short rotation plantations of clones of Gmelina arborea in three spacings

Abstract The first attempts to establish energy crops in the tropical regi­on using short rotation species are premised on the utilization of clones for wood production. Therefore, the present study is aimed at examining the growth aspects (survival, diameter and tree height), leaf architecture (leaf area index [LAI], number and angle of the branches and sylleptic branches), biomass production, as well as biomass flow at the age of 24 months of two clones of Gmelina arborea in short rotation crops within three spacings (1.0x1.0 m, 0.75x0.75 m and 1.0x0.5 m). The results showed an increment with age, as the diameter increa­sed from 3.00 cm at six months to 8.0 cm at 24 months, where­as the total height increased from 2.00 m at six months to 10.00 m at 24 months. Clone survival varied from 20 to 60 %, whereas the LAI, branch angle and sylleptic branches increased with age. The differences between clones appeared after 12 months. Biomass production was similar between clones, from 6 ton/ha at six months to 67 ton/ha at 24 months, with clone 2 showing greater biomass flow than clone 1. On the basis of biomass pro­duction results and the development of diameter as well as height, clone 1 is recommended for spacing 1.0x1.0 m and clo­ne 2 for spacings 0.75x0.75 m and 1.0x0.5 m.

Inducing sylleptic branching in the interspecific pear ‘PremP109’

Use of well-feathered trees when establishing an orchard promotes early cropping; however, many pear cultivars do not readily form sylleptic branches in commercial nurseries. Observations of young trees of the interspecific pear ‘PremP109’ suggest it has an upright habit with minimal natural branching, which leads to slow canopy establishment. Plant growth regulators with cytokinin-like activity have been applied to a range of fruit trees in nurseries to induce sylleptic branching, resulting in well-feathered trees. This investigation compared the efficacy of cyclanilide (CYC) at 5, 10, 50, 100, or 1,000 ppm and 6-benzylaminopurine (BA) at 1000, or 3000 ppm treatments and two controls, on feathering of two-year-old headed ‘Premp109’ nursery trees. All treatments except one control were subsequently sprayed with four weekly applications of gibberellic acid (GA(3)) at 200 ppm, to encourage extension of any sylleptic branches that formed. The control and GA(3) only treatment produced no branches and averaged about four spurs tree(-1). Application of BA or CYC increased the number of spurs and shoots produced, with the lower concentrations of CYC being more effective than higher concentrations. The number of spurs produced doubled for the BA 3,000 ppm, CYC 5 and CYC10 ppm treatments, when compared with the controls. However, the number of extended shoots produced were low, ranging between 0.2 and 2.2 shoots tree(-1). The length of the shoots produced were longest for the BA1000 treatment averaging 203 mm, while the shoot lengths produced by the remaining effective treatments ranged between 27 and 86 mm. These results highlight the difficulty in inducing sylleptic branching in ‘PremP109’, and reinforce the need for tree training systems that utilize the natural non-branching growth habits of fruit trees such as these.

Expression of MdCCD7 in the scion determines the extent of sylleptic branching and the primary shoot growth rate of apple trees.

Branching has a major influence on the overall shape and productivity of a plant. Strigolactones (SLs) have been identified as plant hormones that have a key role in suppressing the outgrowth of axillary meristems. CAROTENOID CLEAVAGE DIOXYGENASE (CCD) genes are integral to the biosynthesis of SLs and are well characterized in annual plants, but their role in woody perennials is relatively unknown. We identified CCD7 and CCD8 orthologues from apple and demonstrated that MdCCD7 and MdCCD8 are able to complement the Arabidopsis branching mutants max3 and max4 respectively, indicating conserved function. RNAi lines of MdCCD7 show reduced gene expression and increased branching in apple. We performed reciprocal grafting experiments with combinations of MdCCD7 RNAi and wild-type 'Royal Gala' as rootstocks and scion. Unexpectedly, wild-type roots were unable to suppress branching in MdCCD7 RNAi scions. Another key finding was that MdCCD7 RNAi scions initiated phytomers at an increased rate relative to the wild type, resulting in a greater node number and primary shoot length. We suggest that localized SL biosynthesis in the shoot, rather than roots, controls axillary bud outgrowth and shoot growth rate in apple.

Impact of RAV1-engineering on poplar biomass production: a short-rotation coppice field trial

BackgroundEarly branching or syllepsis has been positively correlated with high biomass yields in short-rotation coppice (SRC) poplar plantations, which could represent an important lignocellulosic feedstock for the production of second-generation bioenergy. In prior work, we generated hybrid poplars overexpressing the chestnut gene RELATED TO ABI3/VP1 1 (CsRAV1), which featured c. 80% more sylleptic branches than non-modified trees in growth chambers. Given the high plasticity of syllepsis, we established a field trial to monitor the performance of these trees under outdoor conditions and a SRC management.ResultsWe examined two CsRAV1-overexpression poplar events for their ability to maintain syllepsis and their potential to enhance biomass production. Two poplar events with reduced expression of the CsRAV1 homologous poplar genes PtaRAV1 and PtaRAV2 were also included in the trial. Under our culture conditions, CsRAV1-overexpression poplars continued developing syllepsis over two cultivation cycles. Biomass production increased on completion of the first cycle for one of the overexpression events, showing unaltered structural, chemical, or combustion wood properties. On completion of the second cycle, aerial growth and biomass yields of both overexpression events were reduced as compared to the control.ConclusionsThese findings support the potential application of CsRAV1-overexpression to increase syllepsis in commercial elite trees without changing their wood quality. However, the syllepsis triggered by the introduction of this genetic modification appeared not to be sufficient to sustain and enhance biomass production.

Modeling final leaf length as a function of carbon availability during the elongation period

Each leaf is both a sink and a source of carbon that determines the growth of plant structure. Therefore, simulation of individual leaf expansion is essential in modeling plant structural growth. Leaf expansion has been often fitted to logistic sigmoidal functions that require initial and final leaf length, and duration of elongation to be known. A different method, based on the compound interest law, determines leaf length using initial length, relative elongation rate and duration of elongation. We aimed to evaluate which factors are most important in explaining final leaf length variability. Elongation of individual leaves on peach shoots was monitored over 21 days. Individual leaf lengths were fitted to logistic functions to determine their initial and final lengths, and durations of elongation in growing degree hours. Parameters that could affect final leaf length were evaluated: shoot characteristics below the leaf, initial length, duration of elongation, and temperature during the initial days after leaf appearance. Final leaf length had significant relationships with leaf area and length of the shoot axis excluding sylleptic branches, but it was not significantly related to initial length or duration of elongation. Total shoot leaf area and temperature during the initial days after leaf appearance also affected final leaf length. Our results showed that final leaf length is mainly determined by factors acting during leaf elongation. Based on these data, we used compound interest law and carbon availability concepts to develop a mechanistic model of final lengths of individual leaves.

Combining Genome-Wide Information with a Functional Structural Plant Model to Simulate 1-Year-Old Apple Tree Architecture.

In crops, optimizing target traits in breeding programs can be fostered by selecting appropriate combinations of architectural traits which determine light interception and carbon acquisition. In apple tree, architectural traits were observed to be under genetic control. However, architectural traits also result from many organogenetic and morphological processes interacting with the environment. The present study aimed at combining a FSPM built for apple tree, MAppleT, with genetic determinisms of architectural traits, previously described in a bi-parental population. We focused on parameters related to organogenesis (phyllochron and immediate branching) and morphogenesis processes (internode length and leaf area) during the first year of tree growth. Two independent datasets collected in 2004 and 2007 on 116 genotypes, issued from a ‘Starkrimson’ × ‘Granny Smith’ cross, were used. The phyllochron was estimated as a function of thermal time and sylleptic branching was modeled subsequently depending on phyllochron. From a genetic map built with SNPs, marker effects were estimated on four MAppleT parameters with rrBLUP, using 2007 data. These effects were then considered in MAppleT to simulate tree development in the two climatic conditions. The genome wide prediction model gave consistent estimations of parameter values with correlation coefficients between observed values and estimated values from SNP markers ranging from 0.79 to 0.96. However, the accuracy of the prediction model following cross validation schemas was lower. Three integrative traits (the number of leaves, trunk length, and number of sylleptic laterals) were considered for validating MAppleT simulations. In 2007 climatic conditions, simulated values were close to observations, highlighting the correct simulation of genetic variability. However, in 2004 conditions which were not used for model calibration, the simulations differed from observations. This study demonstrates the possibility of integrating genome-based information in a FSPM for a perennial fruit tree. It also showed that further improvements are required for improving the prediction ability. Especially temperature effect should be extended and other factors taken into account for modeling GxE interactions. Improvements could also be expected by considering larger populations and by testing other genome wide prediction models. Despite these limitations, this study opens new possibilities for supporting plant breeding by in silico evaluations of the impact of genotypic polymorphisms on plant integrative phenotypes.

Sylleptic branching in winter-headed apple (Malus × domestica) trees: accession-dependent responses and their relationships with other tree architectural characteristics

Well-feathered apple trees are essential for commercial orchards to optimize yields. However, most cultivars do not form these sylleptic branches readily in commercial nurseries due to high apical dominance. Several treatments exist to promote their formation in the nurseries, one of which is heading. However, not all cultivars are expected to react similarly to these treatments. We studied the branching response of 155 genotypes following heading and its relation to other architectural traits as a function of the cultivar’s genetic background. Trees were grown for two consecutive years after grafting in a nursery, and the main axes were headed in the winter following growth in year 1. After heading, a single shoot was retained when growth resumed in the second year. Plant architectural traits such as growth of the main shoot, internode length, sylleptic branching, etc. were measured before and after heading and were statistically compared using a mixed model. This model showed the effect of heading for all architectural traits studied. In addition significant genotype and genotype × treatment interactions were found. In general, genotypes that showed a more vigorous growth during the first year also reacted more vigorously to heading. Accounting for the genetic substructure of this collection, no clear distinction in tree response could be found except in a small group of individuals that belonged to an F1 mapping population. This study shows that heading is not favorable for all genotypes to promote sufficient sylleptic branching and that other methods are needed to promote branching in these accessions.

Branch induction via prolepsis in apple nursery trees

Branching in fruit trees is mostly cultivar-dependent. However, the branching habit of genotypes might be altered by training methods. This study has been carried out to investigate the tree quality of different methods focused on proleptic and sylleptic branching in the apple nursery. 'Golden Reinders'/'M.9' combination was used as a plant material. Knipboom tree for syllepsis and fruitful tree for prolepsis were chosen. Data were collected for tree quality (branch character, tree height, spur and brindle, tree weight, root: shoot ratio, total leaf area, etc.) and physiological criteria (total carbohydrate, nutrients, etc.). Fruitful tree significantly increased the number of branches (>25 cm) in comparison to knipboom tree. The fruitful tree produced 7.05 branches tree-1 in the first year and 6.97 branches tree-1 in the second year of the trial. The best results for branch crotch angle, spur number, brindle number, trunk diameter and tree height were obtained from fruitful tree treatment in both trial years. Proleptic branching e.g., fruitful which is a new approach in the nurseries found to be a satisfactory method to promote many tree quality and physiological characteristics.

Small GTP-binding protein PdRanBP regulates vascular tissue development in poplar.

BackgroundPrevious research has demonstrated that ectopic expression of Ran-binding protein (RanBP) in Arabidopsis results in more axillary buds and reduced apical dominance compared to WT plants. However, the function of RanBP in poplar, which has very typical secondary growth, remains unclear. Here, the Populus deltoides (Marsh.) RanBP gene (PdRanBP) was isolated and functionally characterized by ectopic expression in a hybrid poplar (P. davidiana Dode × P. bolleana Lauche).ResultsPdRanBP was predominantly expressed in leaf buds and tissues undergoing secondary wall expansion, including immature xylem and immature phloem in the stem. Overexpression of PdRanBP in poplar increased the number of sylleptic branches and the proportion of cells in the G2 phase of the cell cycle, retarded plant growth, consistently decreased the size of the secondary xylem and secondary phloem zones, and reduced the expression levels of cell wall biosynthesis genes. The downregulation of PdRanBP facilitated secondary wall expansion and increased stem height, the sizes of the xylem and phloem zones, and the expression levels of cell wall biosynthesis genes.ConclusionsThese results suggest that PdRanBP influences the apical and radial growth of poplar trees and that PdRanBP may regulate cell division during cell cycle progression. Taken together, our results demonstrated that PdRanBP is a nuclear, vascular tissue development-associated protein in P. deltoides.Electronic supplementary materialThe online version of this article (doi:10.1186/s12863-016-0403-4) contains supplementary material, which is available to authorized users.

Diverse growth and sylleptic branching patterns in Japanese maple cultivars

Branching is a key determinant of architectural quality of ornamental plants. Using plants trained to a single primary shoot, cultivars of Japanese maple (Acer sp.) 'Fireglow', 'Katsura', 'Orangeola', 'Red Emperor', 'Skeeter's Broom' and 'Sango Kaku' presented a diverse range of growth and sylleptic branching patterns. Shoot extension was more vigorous in 'Sango Kaku', which displayed uninterrupted extension to develop more than 30 metamers. In other cultivars, some primary shoots had a pause after extension of approximately six preformed metamers, forming shorter bicyclic shoots (e.g., 'Red Emperor'); and some of the shoots were monocyclic, comprising mostly preformed metamers (e.g., 'Fireglow'). Sylleptic branching in the six cultivars differed in both branching intensity and the location of branches along the primary shoot. 'Sango Kaku' and 'Katsura' featured two intensely branched zones with lower branching frequency between them. 'Orangeola' and 'Skeeter's Broom' had a single branching zone with lower branching intensity located at the basal and middle sections of the parent shoot, respectively. In addition, xylem sap of 'Red Emperor' contained more strigolactone than that of 'Sango Kaku', supporting the hypothesis that sylleptic branching appears to correlate inversely with the amount of strigolactone. The above results support the hypothesis that the occurrence of sylleptic branching and these branches' distribution along the primary shoot are subject to combined hormonal and developmental control. Possible relationships between the primary shoot organogenesis/extension and the time course of sylleptic branching are currently being investigated.

First Report of Rhodococcus Isolates Causing Pistachio Bushy Top Syndrome on 'UCB-1' Rootstock in California and Arizona.

'UCB-1' (Pistacia atlantica × Pistacia integerrima) rootstock is a hybrid cultivar widely used by the U.S. pistachio industry. In the last three years, a large number of micropropagated UCB-1 pistachio rootstocks planted in California and Arizona orchards exhibited shortened internodes, stunted growth, swollen lateral buds, bushy/bunchy growth, stem galls with multiple buds, and twisted roots with minimal lateral branching. Field T-budding success in affected orchards was reduced to approximately 30% with unusual bark cracking often observed around the bud-union. The percentage of abnormal rootstocks within affected orchards varied from 10 to 90%. We have termed the cumulative symptoms "pistachio bushy top syndrome" (PBTS) to describe these affected trees. Two isolates, both containing virulence factors from the phytopathogen Rhodococcus fascians, were identified on symptomatic trees in field and nursery samples. Micropropagated UCB-1 trees inoculated with the Rhodococcus isolates exhibited stunted growth, shortened internode length, swollen lateral buds, sylleptic branching, and differences in root morphology, compared with control UCB-1 trees. To our knowledge, this is the first report of Rhodococcus isolates, related to Rhodococcus fascians, causing disease on a commercial tree crop and the results presented indicate that this organism is responsible at least in part for PBTS in California and Arizona.

Simulation and Quantitative Analysis of Branching Patterns of the Plum Tree

Background and Aims: Pruning fruit tree is undoubtedly a critical cultural practice which leads to sustainable production along with profitability of the trees. Several limitations of classic approaches pertaining to studying pruning techniques based mostly on fruit yields and quality evaluations have kept us from thoroughly understanding the growth habits of branches under field conditions. A simulation model of branching patterns of the plum tree (Prunus salicina cv. Sanhua) introduced in this paper enables both non-professionals and professionals to better understand and predict pruning effects on branching pattern and fruiting habit of the trees. The visual comparison of branching and fruiting characteristic of the prunedparent shootprovides immediate feedback on different pruning intensities at the level of shoots.Methods: Semi-Markov chains were built with diverse initial probabilities, transition probabilities and occupancy distributions to describe the number of occurrence of girl shoots along the pruned parent shoot. Branching structures were reconstructed using AmapSim computer software with different shoot types, considering topological and geometrical functions.Key Results: The results demonstrated different branching zones in the pruned parent shoot were found in the same order. Moderate heading back and slight heading back parent shoots differed in short shoot position. Of all pruning intensities, the branching zone in severe heading back parent shoots was shorter than the sylleptic branching zone. The three-dimensional reconstruction images of pruned parent shoots displayed illustrative examples to elucidate proper pruning technique among three pruning intensities.Conclusions: Severe heading back parent shoot had a strong branching capability. In comparison with moderate heading back, slight heading back parent shoot had a higher proportion of fruiting zones, therefore the latter is usually considered balancing vegetative and reproductive growth in the conventional pruning of plum trees.The stochastic model could serve as a feasibility groundwork against which quantitative differences in branching structures of prune parent shoot under different pruning systems can be compared.

Verification of a phenotypic discrimination method for hybrid larch seedlings using DNA markers

The hybrid between Kuril larch (Larix gmelinii var. japonica) and Japanese larch (L. kaempferi) is an important afforestation tree species in Hokkaido, Japan, because of its rapid juvenile growth, straight stem, and resistance to bark gnawing by voles. To produce desirable hybrid seedlings, precise seedling discrimination is essential. However, continuous variations in morphological and phenological traits occur across L. gmelinii var. japonica × L. kaempferi and L. gmelinii var. japonica × L. gmelinii var. japonica seedlings. Therefore, we used DNA markers to verify and improve the morphological and phenological discrimination method. We collected seeds from an interspecific seed orchard and, using chloroplast DNA analysis, we showed that the hybridization rates of 1-year-old seedlings were different between years (2004, 23.2 %; 2005, 53.6 %) and between mother trees (2004, 5.8–39.4 %; 2005, 20.0–81.0 %). Discriminant analyses revealed that the root collar diameter of 2-year-old seedlings, number of sylleptic branches of 2-year-old seedlings, and day of terminal bud set in 1- and 2-year-old seedlings are traits that aid in discriminating hybrid seedlings. The proportions of correctly discriminated individuals were found to be 81.7–88.2 % when using improved phenotypic discrimination methods. These methods adopted traits with high discrimination abilities during discriminant analyses and determined the selection intensity according to the hybridization rate estimated from the DNA markers. In contrast, the proportions of correctly discriminated individuals obtained using the current method were lower, 72.7–78.5 %, because this method was based on seedling height and adopted a constant selection intensity.

USING HIDDEN SEMI-MARKOV CHAINS TO COMPARE THE SHOOT STRUCTURE OF THREE DIFFERENT ALMOND CULTIVARS

Shoot structure, resulting from lateral branching and flowering patterns, determines final tree form, fruit bearing habit, and cropping potential. The genetic make-up of different cultivars controls vegetative and reproductive growth, but few structural studies have been done to systematically describe almond shoot structure. A specific class of Markovian models, referred to as hidden semi-Markov chains (HSMC), has been proposed to identify and characterize branching and flowering patterns in fruit trees. This type of model is particularly appropriate when the shoot structure is organized as a succession of homogeneous branching zones and captures the variable character of the observed patterns. This study reports the first almond HSMC analysis of shoot structure based on data collected from epicormic shoots and five length categories of proleptic shoots in three almond cultivars with distinctly different tree architecture. 'Nonpareil' is the most important cultivar grown in California and has a relatively spreading tree habit. 'Aldrich' is a newer cultivar with an upright growth habit, and 'Winters' has a spreading habit with a high tendency for sylleptic branching on proleptic shoots. Shoots of these three cultivars were analyzed to determine different zones that could be classified according to lateral bud fates and the number of flower buds at each node. This modeling technique showed that almond shoot structures are highly organized and predictable. Substantial differences were found in the structure of the proleptic shoots of similar length, among the cultivars, but fewer differences were found among epicormic shoots. For long shoots, 'Aldrich' had the highest probability of flower buds and 'Winters' had the greatest lateral branching distributed along shoots. 'Nonpareil' had similar branching probabilities as 'Aldrich' and its probability of flower buds was similar to 'Winters'. It is anticipated that these HSMC will be useful for identifying desirable shoot structures for cultivar improvement and will help to explain the differences in tree architecture and cropping potential among cultivars. (Resume d'auteur)

Within-population variability in architectural traits and suitability to forestry conditions in Nothofagus nervosa (= N. alpina; Nothofagaceae)

There is evidence that Nothofagus nervosa (= N. alpina) is suitable for timber production in temperate regions due to its wood quality and fast growth. However, high intra-specific variability in the architectural traits of this species limits its usefulness. This study was aimed at evaluating intra-specific variability in the architecture of N. nervosa trees at the population level, with emphasis on traits related to the suitability of trees for timber production. The size of 13-year-old trees installed in an experimental field population and the extent of differentiation between trunk and branches were compared among families (trees derived from different mother trees). The large majority of trees exhibited architectural features indicative of high suitability for timber production: clear differentiation between trunk and main branches and few occurrences of permanent trunk forks, apex deaths, and sylleptic branching. Trees belonging to different families differed in height and trunk diameter. Micro-environmental conditions had a very significant effect on most architectural traits, including the trunk differentiation. N. nervosa emerges as a suitable option for timber production in temperate regions. Trunk growth seems to be under both environmental and genetic control in this species.

After initial invigoration by heading, young pear trees show reduction in axis vigour and increased propensity to flower.

Fast establishment of the canopy in young trees, followed by reduced vegetative vigour and precocity are desirable traits in fruit production. Severe heading (cutting back the primary axis of the tree after the first year of growth) to induce branching is a nursery practice to increase early fruit yield. Our aim was to provide a systematic study of the responses of young pear trees to severe heading. We used an experimental system with two scion genotypes and three rootstocks to create trees with contrasting branching habits and vigour. The trees' trunks were headed and a single bud was allowed to outgrow in the following season. Architectural analysis was used to quantify the development of regenerated trees. In the first year after heading, the growth of the primary axes and, depending on the scion genotype, the sylleptic branching of regenerating trees, were invigorated. In the second year, the percentage of budbreak was also increased, but the shoot growth was greatly reduced. Axis propensity to flower in spring of the third year of growth was increased. The new insights into the effects of heading on tree aging and flowering will be used for guiding the best approaches to managing young pear trees.

Importance of crown architecture for leaf area index of different Populus genotypes in a high-density plantation

Crown architecture is an important determinant of biomass production and yield of any bio-energy plantation since it determines leaf area display and hence light interception. Four Populus genotypes-of different species and hybrids and with contrasting productivity and leaf area-were examined in terms of their branch characteristics in relation to crown architecture during the first and second growing seasons after plantation establishment. The trees were planted at high density (8000 ha(-1)) on two different former land use types, cropland and pasture. We documented significant differences in branch architecture among the genotypes and for the first year among the former land use types. Land use effects only affected factors not related to canopy closure and wood production, and decreased after the first growing season. This suggested that both former land use types were equally suited for the establishment success of a poplar bio-energy plantation. Tree height and branch dimensions-branch diameter and branch length-were the most important determinants of wood production and maximum leaf area index. Despite the secondary importance of the number of sylleptic branches, these branches contributed significantly to the total leaf area in three out of the four studied genotypes. This indicated that enhanced syllepsis accelerates leaf area development and hence carbon assimilation, especially in the early stages of a high-density plantation with poplar.

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.

Bringing trees into the fuel line

Bringing trees into the fuel line

CsRAV1 induces sylleptic branching in hybrid poplar

• Sylleptic branching in trees may increase significantly branch number, leaf area and the general growth of the tree, particularly in its early years. Although this is a very important trait, so far little is known about the genes that control this process. • This article characterizes the Castanea sativa RAV1 gene, homologous to Arabidopsis TEM genes, by analyzing its circadian behavior and examining its winter expression in chestnut stems and buds. Transgenic hybrid poplars over-expressing CsRAV1 or showing RNA interference down-regulated PtaRAV1 and PtaRAV2 expression were produced and analyzed. • Over-expression of the CsRAV1 gene induces the early formation of sylleptic branches in hybrid poplar plantlets during the same growing season in which the lateral buds form. Only minor growth differences and no changes in wood anatomy are produced. • The possibility of generating trees with a greater biomass by manipulating the CsRAV1 gene makes CsRAV1 transgenic plants promising candidates for bioenergy production.