Project description:Populus trichocarpa has been studied as a model poplar species through biomolecular approaches and was the first tree species to be genome sequenced. In this study, we employed a high throughput RNA-sequencing (RNA-seq) mediated leaf transcriptome analysis to investigate the response of four different Populus davidiana cultivars to drought stress. Following the RNA-seq, we compared the transcriptome profiles and identified two differentially expressed genes (DEGs) with contrasting expression patterns in the drought-sensitive and tolerant groups, i.e., upregulated in the drought-tolerant P. davidiana groups but downregulated in the sensitive group. Both these genes encode a 9-cis-epoxycarotenoid dioxygenase (NCED), a key enzyme required for abscisic acid (ABA) biosynthesis. The high-performance liquid chromatography (HPLC) measurements showed a significantly higher ABA accumulation in the cultivars of the drought-tolerant group following dehydration. The Arabidopsis nced3 loss-of-function mutants showed a significantly higher sensitivity to drought stress, ~90% of these plants died after 9 days of drought stress treatment. The real-time PCR analysis of several key genes indicated a strict regulation of drought stress at the transcriptional level in the P. davidiana drought-tolerant cultivars. The transgenic P. davidiana NCED3 overexpressing (OE) plants were significantly more tolerant to drought stress as compared with the NCED knock-down RNA interference (RNAi) lines. Further, the NCED OE plants accumulated a significantly higher quantity of ABA and exhibited strict regulation of drought stress at the transcriptional level. Furthermore, we identified several key differences in the amino acid sequence, predicted structure, and co-factor/ligand binding activity of NCED3 between drought-tolerant and susceptible P. davidiana cultivars. Here, we presented the first evidence of the significant role of NCED genes in regulating ABA-dependent drought stress responses in the forest tree P. davidiana and uncovered the molecular basis of NCED3 evolution associated with increased drought tolerance.
Project description:Just as animal monozygotic twins can experience different environmental conditions by being reared apart, individual genetically-identical trees of the genus Populus can also be exposed to contrasting environmental conditions by being grown in different locations. As such, clonally-propagated Populus trees provide an opportunity to interrogate the impact of individual environmental history on current response to environmental stimuli. To test the hypothesis that current responses to an environmental stimulus, drought, are contingent on environmental history, the transcriptome-level drought responses of three economically important hybrid genotypes: DN34 (Populus deltoides x P. nigra); Walker (P. deltoides var. occidentalis x (P. laurifolia x P. nigra)); and, Okanese (‘Walker’ x (P. laurifolia x P. nigra)) derived from two different locations were compared. Strikingly, differences in transcript abundance patterns in response to drought were based on differences in geographic origin of clones for two of the three genotypes. This observation was most pronounced for the genotypes with the longest time since establishment and last common propagation. Differences in genome-wide DNA methylation paralleled the transcriptome level trends, where the clones with the most divergent transcriptomes and clone history had the most marked differences in the extent of total DNA methylation, suggesting an epigenetic basis for the clone-history-dependent transcriptome divergence. The data provide insights into the interplay between genotype and environment in the ecologically and economically important Populus genus, with implications for both the industrial application of Populus trees, and the evolution and persistence of these important tree species.
Project description:Drought is a major limitation to the growth and productivity of trees in the ecologically and economically important genus Populus. The ability of Populus trees to contend with drought is a function of the responsiveness of their genome to this environmental insult, involving reconfiguration of the transcriptome to appropriately remodel growth, development and metabolism. The Populus drought transcriptome is shaped by interspecific genotypic variation, but the extent to which intraspecific variation shapes the drought transcriptome has not yet been examined. Here we test hypotheses aimed at examining the extent of intraspecific variation in the drought transcriptome. Transcriptome remodeling in response to water-deficit conditions was examined in six different Populus balsamifera L. genotypes using Affymetrix GeneChip technology. There were significant differences in the transcriptomes of the genotypes in response to water-deficit conditions; however, a common species-level response could also be identified across all individuals. Genotypes that had more similar drought-responsive transcriptomes also had fewer genotypic differences, as determined by microarray-derived single feature polymorphism (SFP) analysis, suggesting that responses may be conserved across individuals that share a greater degree of genotypic similarity. This work highlights the fact that a core species-level response can be defined; however, the underpinning genotype-derived complexities of the drought response in Populus must be taken into consideration when defining both species- and genus-level responses.
Project description:We sought to generate a comprehensive proteomic profile for a Populus plant that captures protein abundance behavioral differences in mature leaves under various water deficit conditions. The sudden infliction of severe drought is unlikely to reflect what naturally happens to soil-grown plants. Therefore, rather than exposing plants to severe dehydration via the application of concentrated osmotica (e.g., polyethylene glycol or mannitol), we aimed to monitor plants exposed to prolonged drought as well as plants frequently experiencing cyclic drought. For the progressive drought experiment, herein referred to as acute drought, water will be withheld from the plants for a certain period of time until symptoms of wilting are observed. From this drought treatment, protein abundance changes that occur because of declining water potentials that consequently lead to worsening plant health will provide new insights to biological pathways in response to severe drought conditions. On the other hand, as a consequence of simulating a more natural condition, the cyclic drought treatment will provide novel insights into drought recovery and coping mechanisms. As first noted in a meta-analysis of microarray experiments comparing different water deficit-related treatments3, one consequence of analyzing multiple treatment conditions is that we expect only a few differentially abundant proteins to be common to both treatments. Therefore, we implemented a bioinformatic framework to provide an overall integrative picture of the conserved drought markers but also meaningful divergences in functional behavioral responses between the two experiments.
Project description:As exposure to episodic drought can impinge significantly on forest health and the establishment of productive tree plantations, there is great interest in understanding the mechanisms of drought response in trees. The ecologically dominant and economically important genus Populus, with its sequenced genome, provides an ideal opportunity to examine transcriptome level changes in trees in response to a drought stimulus. The transcriptome level drought response of two commercially important hybrid Populus clones (P. deltoides · P. nigra, DN34, and P. nigra · P. maximowiczii, NM6) was characterized over a diurnal period using a 4 · 2 · 2 completely randomized factorial ANOVA experimental design (four time points, two genotypes, and two treatment conditions) using Affymetrix Poplar GeneChip microarrays. Notably, the specific genes that exhibited changes in transcript abundance in response to drought differed between the genotypes and/or the time of day that they exhibited their greatest differences. This study emphasizes the fact that it is not possible to draw simple, generalized conclusions about the drought response of the genus Populus on the basis of one species, nor on the basis of results collected at a single time point. The data derived from our studies provide insights into the variety of genetic mechanisms underpinning the Populus drought response, and provide candidates for future experiments aimed at understanding this response across this economically and ecologically important genus.