Über Eine in der Natur Gefundene Gigasform von Populus Tremula

Whole genome duplication of wild-type and CINNAMYL ALCOHOL DEHYDROGENASE1-downregulated hybrid poplar reduces biomass yield and causes a brittle apex phenotype in field-grown wild types

The potential of whole genome duplication to increase plant biomass yield is well-known. In Arabidopsis tetraploids, an increase in biomass yield was accompanied by a reduction in lignin content and, as a result, a higher saccharification efficiency was achieved compared with diploid controls. Here, we evaluated whether the results obtained in Arabidopsis could be translated into poplar and whether the enhanced saccharification yield upon alkaline pretreatment of hairpin-downregulated CINNAMYL ALCOHOL DEHYDROGENASE1 (hpCAD) transgenic poplar could be further improved upon a whole genome duplication. Using a colchicine treatment, wild-type (WT) Populus tremula x P. alba cv. INRA 717-1B4, a commonly used model clone in tree biotechnology research, and hpCAD tetraploids were generated and grown in the greenhouse. In parallel, WT tetraploid poplars were grown in the field. In contrast to Arabidopsis, a whole genome duplication of poplar had a negative impact on the biomass yield of both greenhouse- and field-grown trees. Strikingly, field-grown WT tetraploids developed a brittle apex phenotype, i.e., their tip broke off just below the apex. In addition, the chromosome doubling altered the biomass composition of field-grown, but not of greenhouse-grown tetraploid poplars. More specifically, the lignin content of field-grown tetraploid poplars was increased at the expense of matrix polysaccharides. This increase in lignin deposition in biomass is likely the cause of the observed brittle apex phenotype, though no major differences in stem anatomy or in mechanical properties could be found between di- and tetraploid WT poplars grown in the field. Finally, without biomass pretreatment, the saccharification efficiency of greenhouse- and field-grown WT diploids was not different from that of tetraploids, whereas that of greenhouse-grown hpCAD tetraploids was higher than that of greenhouse-grown diploids. Upon alkaline pretreatment, the saccharification yield of diploids was similar to that of tetraploids for all genotypes and growth conditions tested. This study showed that a whole genome duplication in hybrid WT and hpCAD poplar did neither result in further improvements in biomass yield, nor in improved biomass composition and, hence, saccharification performance.

Transcriptome comparison of different ploidy reveals the mechanism of photosynthetic efficiency superiority of triploid poplar

Triploid poplars have obvious growth advantages, especially in leaf development and photosynthetic characteristics, but the molecular mechanism has not been revealed yet. In order to better understand the regulation mechanisms of leaf and chlorophyll development in the triploid poplars, we combined the leaf phenotypic data with the transcriptomic data of the 5th, 10th, and 25th leaves from triploid and diploid poplars, using weighted gene co-expression network analysis (WGCNA), and revealed that PpnGRF5-1 had a strong correlation with leaf development and net photosynthetic rate (Pn). PpnGRF5-1 overexpression transgenic plants showed that the leaf area, Pn, and chlorophyll concentration were significantly increased. Transcriptomic data analysis of the third leaf from PpnGRF5-1 overexpression transgenic plants showed that PpnGRF5-1 could up-regulate the expression levels of chlorophyll synthesis genes and down-regulate the transcription of chlorophyll degradation enzymes. Overall, our studies have greatly expanded our understanding of the molecular mechanisms regulating triploid growth dominance.

Megaspore Chromosome Doubling in Eucalyptus urophylla S.T. Blake Induced by Colchicine Treatment to Produce Triploids

Triploids generally provide an advantage in vegetative growth in forest trees. However, the technique of triploid breeding is still an open field in the Eucalyptus tree species. This study aims to explore the colchicine treatment technique for megaspore chromosome doubling to establish triploids in this tree species. Cytological observation on microsporogenesis and megasporogenesis was carried out to guide megaspore chromosome doubling induced by colchicine treatment. Ploidy level in progenies was detected by flow cytometry and somatic chromosome counting. A relationship between microsporogenesis and megasporogenesis was established to guide the colchicine treatment. Seven triploids were obtained in the progenies, and the highest efficiency of triploid production was 6.25% when the flower buds underwent a 0.25% colchicine solution treatment for 6 h using an aspiration method seven days after the first observation of leptotene during microsporogenesis on the floral branch. Cytological analysis showed that the megasporocyte from leptotene to diakinesis may be the optimal period for megaspore chromosome doubling by colchicine treatment. Plant height, ground diameter, leaf area, and the photosynthetic parameter of triploid eucalypt were significantly higher than those of the diploid plant at 6 months old. Hybridization with 2n megaspores induced by colchicine treatment is an effective way for Eucalyptus triploid breeding. These results should accelerate the development of advanced germplasms in this tree species.

Molecular Identification and Karyological Analysis of a Rampant Aspen Populus tremula L. (Salicaceae) Clone

A rampant highly heterozygous aspen (Populus tremula L.) clone "Meshabash" has been revealed in course of population genetic diversity analysis in a native stand in the Republic of Tatarstan, Russia. Here we report the results of karyological analysis showing that this highly vigorous clone is diploid (2n = 38) while typically triploid aspen demonstrates increased growth rate and resistance to aspen trunk rot caused by fungus Phellinus tremulae. By means of DNA identification of a series of model trees using 14 SSR loci we outlined the area occupied by this clone (at least 1.94 ha) and demonstrated that its ramets constitute 40 out of 48 genotyped trunks on the plot with the maximal distance between ramets 254 m. Since aspen is able to regenerate after cutting or die-off of maternal tree by root suckers at a distance up to 20-35 m this assumed that current stand appeared as a result of such spreading from an ortet tree during at least 5 generations. Trunk rot damage in the wood of model trees indicated low influence of this pathogen on viability and performance of the studied clone that can be associated with its extreme heterozygosity level (0.926) exceeding all the studied trees in this research plot and in three other control samples.

Comparative analysis of growth and photosynthetic characteristics of (Populus simonii × P. nigra) × (P. nigra × P. simonii) hybrid clones of different ploidides

To evaluate differences among poplar clones of various ploidies, 12 hybrid poplar clones (P. simonii × P. nigra) × (P. nigra × P. simonii) with different ploidies were used to study phenotypic variation in growth traits and photosynthetic characteristics. Analysis of variance showed remarkable differences for each of the investigated traits among these clones (P < 0.01). Coefficients of phenotypic variation (PCV) ranged from 2.38% to 56.71%, and repeatability ranged from 0.656 to 0.987. The Pn (photosynthetic rate) photosynthetic photon flux density (PPFD) curves of the 12 clones were S-shaped, but the Pn-ambient CO2 (Ca) curves were shaped like an inverted "V". The stomatal conductance (Gs)-PPFD and transpiration rate (Tr)-PPFD curves had an upward tendency; however, with increasing PFFD, the intercellular CO2 concentration (Ci)-PPFD curves had a downward tendency in all of the clones. The Pn-PPFD and Pn-Ca curves followed the pattern of a quadratic equation. The average light saturation point and light compensation point of the triploid clones were the highest and lowest, respectively, among the three types of clones. For Pn-Ca curves, diploid clones had a higher average CO2 saturation point and average CO2 compensation point compared with triploid and tetraploid clones. Correlation analyses indicated that all investigated traits were strongly correlated with each other. In future studies, molecular methods should be used to analyze poplar clones of different ploidies to improve our understanding of the growth and development mechanisms of polyploidy.

Early selection of novel triploid hybrids of shrub willow with improved biomass yield relative to diploids

BACKGROUND

Genetic improvement of shrub willow (Salix), a perennial energy crop common to temperate climates, has led to the development of new cultivars with improved biomass yield, pest and disease resistance, and biomass composition suitable for bioenergy applications. These improvements have largely been associated with species hybridization, yet little is known about the genetic mechanisms responsible for improved yield and performance of certain willow species hybrids.

RESULTS

The top performing genotypes in this study, representing advanced pedigrees compared with those in previous studies, were mostly triploid in nature and outperformed current commercial cultivars. Of the genotypes studied, the diploids had the lowest mean yield of 8.29 oven dry Mg ha-1 yr-1, while triploids yielded 12.65 Mg ha-1 yr-1, with the top five producing over 16 Mg ha-1 yr-1. Triploids had high stem area and height across all three years of growth in addition to greatest specific gravity. The lowest specific gravity was observed among the tetraploid genotypes. Height was the early trait most correlated with and the best predictor of third-year yield.

CONCLUSIONS

These results establish a paradigm for future breeding and improvement of Salix bioenergy crops based on the development of triploid species hybrids. Stem height and total stem area are effective traits for early prediction of relative yield performance.

Plant self-defense mechanisms against oxidative injury and protection of the forest by planting trees of triploids and tetraploids

The depletion of the ozone layer, and the resulting substantial increase in incident ultraviolet (UV) irradiation and subsequent oxygen radical formation on the Earth, have caused an extensive variety of damage to the world's forests. Superoxide dismutase (SOD), catalase, and glutathione peroxidase (GSH-Px), which scavenge harmful oxygen radicals and inhibit lipid peroxides, were examined in two types of Japanese cedars, black pines, and cypresses, namely those with leaves showing premature withering, shedding, or dying and those with leaves not showing these effects prematurely. The effect of homogenates from these trees on lipid peroxide formation in a reaction system which UV light induces was also studied. The results indicate that strong black pines have significantly higher SOD activities than ordinary black pines, the leaves of which prematurely wither or die. Remarkably, trees that had triploid or tetraploid chromosomes showed higher SOD levels than diploid trees and markedly inhibited lipid peroxide formation since the SOD gene resides on a chromosome. This was especially true of plus trees of Japanese cypress, some of which had five times higher SOD activities than common Japanese cypresses although GSH-Px appears to play less of a role in this regard. Rice leaves and osmunda which are resistant to UV damage showed markedly higher SOD and GSH-Px activity. Our experiments suggest that the trees that have high SOD can protect themselves by scavenging oxygen radicals induced by UV irradiation and inhibit harmful lipid peroxide formation. In order to protect forests from oxidative damage by UV light, we should plant trees of natural mutants and artificially crossed triploids and tetraploids.