Tree physiology最新文献

Drought and episodic drought events are major impending impacts of climate change, limiting the productivity of plants and especially trees due to their inherent high transpiration rates. One common mechanism used by plants to cope with drought stress is to change the composition of their leaf cuticular waxes. Cuticular waxes are essential for controlling non-stomatal water loss and are typically composed of a homologous series of very-long-chain fatty acid-derived compounds, as well as flavonoids, tocopherols, triterpenoids, and phytosterols. In this study, we compared the cuticular waxes of 339 natural accessions of Populus trichocarpa (Torr. & Gray) (black cottonwood) grown under control and drought conditions in a common garden. A Genome-Wide Association Study (GWAS) was then used to identify candidate genes associated with cuticular wax biosynthesis and/or its regulation. Although no major differences were observed in total wax load when subject to drought conditions, the amounts of the individual wax constituents were indeed responsive to drought. Specifically, changes in alkenes, alcohols, esters and aldehydes were evident, and suggest that they contribute to the drought response/tolerance in poplar. GWAS uncovered several genes linked to fatty acid biosynthesis, including CER1, CER3, CER4, FATB, FAB1, FAR3, FAR4, KCS and a homologue of SOH1, as well as other candidate genes that may be involved in coordinating the drought responses in poplar trees. Our findings provide new evidence that genotype-specific shifts in wax composition, rather than total wax accumulation, contribute to drought adaptation in poplar. Additionally, we show that genetic variation in key wax biosynthetic genes drives cuticular wax plasticity in P. trichocarpa under drought, identifying putative molecular targets for improving stress resilience in trees. This study expands our understanding of the adaptive mechanisms of the cuticle and their potential for enhancing drought tolerance in poplar species.

The influence of nitrogen on wood formation is well established. To gain insight into the underlying molecular mechanism, we first identified genes in 14 gene families that are involved in nitrogen uptake and metabolism in European aspen (Populus tremula L.) genome annotation. Gene expression data from a de novo RNA sequencing (RNA-seq) analysis and data available from the AspWood database (plantgenie.org) provided putative candidate genes for the uptake of nitrate, ammonium and amino acids from the xylem sap as well as their further assimilation in the secondary xylem tissues of the stem. For a population-wide analysis of the nitrogen-related genes, we utilized RNA-seq data from the cambial region of the stems of 5-year-old aspen trees, representing 99 natural aspen accessions, and compared the expression of the nitrogen-related genes to stem diameter. Novel regulatory interactions were identified in expression quantitative loci and co-expression network analyses in these data. The expression of certain nitrate and amino acid transporters correlated negatively with stem diameter, suggesting that excessive nitrogen retrieval from the xylem sap suppresses radial growth of the stem. The expression of a glutamine synthetase correlated with the expression of these transporters, a link further supported by increased plant growth in transgenic glutamine synthetase overexpressing trees. This study provides insight into the genetic basis of nitrogen uptake and assimilation and its connection to wood formation, providing interesting targets for improving nitrogen-use efficiency and growth of aspen trees.

Wood is a vital renewable resource for energy, construction and pulp production. Understanding the molecular mechanisms governing wood formation is therefore crucial for both basic research and applied forestry. The xylem, a major component of wood, plays a crucial role in water transport and mechanical support in trees, requiring a robust secondary cell wall to endure water pressure and support the tree's weight. Gaining deeper insight into xylem cell differentiation is therefore important for both fundamental biological research and industrial applications. In vitro systems for inducing xylem cell differentiation have been developed in various plants, including Arabidopsis thaliana, where key regulators such as the VASCULAR-RELATED NAC DOMAIN transcription factors (TFs) have been identified. However, research on coniferous trees remains limited, with most studies focusing on morphological aspects with limited molecular analysis. In this study, we developed an efficient xylem cell induction system for Cryptomeria japonica D. Don using bikinin, a glycogen synthase kinase 3 inhibitor, in combination with cytokinin, auxin and brassinolide. This system induced ectopic xylem cells in the somatic embryos and cotyledons of seedlings within 2 weeks, significantly faster than methods reported in previous studies. We conducted a comprehensive time-series transcriptome analysis during xylem cell induction in somatic embryos and identified genes expressed throughout the course of xylem cell formation. Our analysis revealed a sequential upregulation of key regulatory genes, including VND- and MYB-like TFs, followed by genes involved in cellulose biosynthesis, suggesting their role in tracheary element formation. These findings suggest that the molecular mechanisms regulating xylem cell formation in the gymnosperm C. japonica are fundamentally conserved with the NAC-MYB transcriptional network known in angiosperms.

Efficient production and processing of poplar biomass feedstock requires costly pretreatments and enzyme additives. Transgenic alterations of poplar can reduce the need for these inputs by increasing biomass, improving lignocellulose quality and enhancing nutrient uptake. Previously, a transgenic line of poplar expressing a bacterial hyperthermophilic endoglucanase (TnCelB) in Populus alba × grandidentata (P39) was developed and characterized. This study reports the effects on the TnCelB transgenic poplar line under a reduced nutrient treatment. Overall, the nutrient treatment was the source of more observed significant differences than the genotype. Wild type and TnCelB poplar had similar responses in biomass allocation and net photosynthesis. TnCelB trees had a wrinkled leaf phenotype and relative to wild type, had reduced total biomass, reduced water-use efficiency, and a decreased proportion of cellulose to hemicellulose and lignin. In low nutrient conditions, TnCelB trees had increased structural carbohydrates with stable lignin values. The TnCelB line presents a viable option for poplar biomass feedstock, offering biomass comparable to wild type poplar and more efficient processing, with only mild negative phenotypes.

Heartwood formation is a complex process that contributes to ensuring the integrity of trunks and the longevity of trees. We examined this mechanism in the tropical angiosperm Sextonia rubra (Mez.) van der Werff in relation to the spatial distribution of specialized metabolites and their functional role at the scale of a mature individual. Heartwood formation was analyzed starting from the examination of one of its properties, namely the decay resistance, of the different S. rubra wood tissues (sapwood, heartwood and pith) using soil bed tests. Annotation and identification of the metabolites present in ethyl acetate extracts were carried out by reverse-phase liquid chromatography coupled to a tandem mass spectrometer (RPLC-ESI-MS/MS) and molecular networks. Following the application of supervised statistical analyses and the use of glutathione S-transferases enzymatic assays, the specialized metabolites of interest were quantified radially and longitudinally in the different tissues using a RPLC-ESI-HRMS system. Heartwood and pith were shown to resist degradation after a 10-month exposure to forest soil, with no effect of the heartwood cambial age. Molecular diversity was specific to each tissue type, with flavonoids and butanolides detected in bark and sapwood, while alkaloids and butyrolactones were identified in heartwood and pith. Supervised analyses and enzyme assays suggested that alkaloids and butyrolactones play a role in the resistance of internal tissues to degradation. Butyrolactone concentrations peaked in the middle heartwood but remained homogeneous longitudinally, while alkaloid concentrations were uniform longitudinally and radially in the heartwood. In conclusion, the resistance of heartwood and pith to fungal degradation was correlated with the accumulation of lactones and alkaloids. While butanolide precursors of butyrolactones have been detected in the sapwood, alkaloids appear to be directly biosynthesized in the heartwood. This suggests that the biosynthesis and accumulation of specialized metabolites during heartwood formation is specific to each molecular family.

Flooding poses a substantial challenge to plant survival and productivity, particularly in riparian genera like Populus. This study examines the physiological, morphological, metabolic and molecular responses of Populus deltoides Bartram ex Marshall 'D-124' and P. trichocarpa Torr. & Gray × P. deltoides hybrid clone '52-225' under control and inundated conditions to identify differences in flooding tolerance. Under flooding conditions, physiological and cellular stress was more pronounced in P. deltoides 'D-124' than in the hybrid clone '52-225,' as evidenced by lower transpiration (E), photosynthesis (A) and chlorophyll content. In contrast, '52-225' showed reduced reactive oxygen species accumulation, suggesting better cellular function under stress. Morphologically, '52-225' produced more shoot-born roots, which likely enhance oxygen transport and metabolic activity during flooding. Metabolite profiling revealed both overlapping and distinct patterns of sugar and amino acid accumulation between genotypes. Gene expression analysis revealed that flooding-responsive genes, including ALCOHOL DEHYDROGENASE 1 and HYPOXIA RESPONSIVE ERF 2, were activated in both genotypes, with a more pronounced response noted in '52-225'. These findings extend our understanding of flooding tolerance mechanisms in Populus by connecting physiological traits, stress responses and genetic regulation. This research contributes to the development of more flooding-resilient poplar varieties, with potential applications in breeding and restoration programs for flooding-prone environments.

The HUGO Gene Nomenclature Committee (www.genenames.org), which has been naming human genes for over 40 years, has been tasked with establishing an official gene nomenclature system for the black cottonwood tree Populus trichocarpa (Torr. & Gray). Here, we review the factors that must be considered when establishing gene nomenclature guidelines. What makes a good gene symbol, and what lessons can be learned from other nomenclature projects? Are there particular challenges associated with naming genes in poplar species? We look at the published gene symbols for Populus and highlight some issues, e.g., the same symbols being used for different genes, and diverse approaches to naming in gene families. What approaches can we take to resolving such conflicts? Since community adoption is key to the success of any nomenclature initiative, we have surveyed poplar researchers for feedback on draft guidelines and discussed some of the issues raised. Finally, we discuss the sustainability of such infrastructure projects-if we build it, will they come and who will fund the ongoing work?

How co-existing species of canopy trees and understory shrubs differentially respond to global warming may affect treeline ecotone dynamics, yet their growth trends and potential underlying ecophysiological mechanisms remain understudied. Here, we used dendrochronology and stable carbon isotope analysis to compare the stem radial growth, intrinsic water-use efficiency (iWUE) and climate sensitivity of co-occurring coniferous trees (Abies fabri Craib) and broadleaved shrubs (Rhododendron faberi subsp. prattiiradial) at a treeline ecotone site in the southeast Tibetan Plateau. The results revealed that the shrub's growth rate has increased significantly over the past 50 years (1973-2022) (P < 0.05), while the growth trend of co-existing trees did not increase significantly. Furthermore, compared with nearby trees, the radial growth of shrubs was more strongly positive correlated with temperature and moisture conditions during the growing season (May-October). Nonetheless, during the more recent 1990-2022 period, iWUE of both woody plant species steadily increased with a rising atmospheric CO2 concentration. Overall, our results suggest that at the treeline ecotone, morphological growth and functional trait differences between coniferous trees and broadleaved shrubs, as well as interactions within and between species, may drive divergent plant physiological processes and ecological strategies in response to rapid global warming.

Inorganic phosphorus (Pi) is an indispensable nutrient for plant growth and development. However, a significant portion of soil Pi is mineralized and becomes fixed in forms that are not readily available for plant uptake. In response to Pi deficiency, plants have evolved adaptive strategies to modify their root architecture, thereby optimizing Pi acquisition from the soil. However, the molecular mechanisms underpinning these responses in woody plants remain largely unexplored. In this study, we found that GROWTH-REGULATING FACTOR 1 (GRF1) expression is significantly and rapidly upregulated in both roots and leaves of poplar under Pi-limited conditions. Overexpression of GRF1 in poplar enhances root development and confers increased tolerance to Pi starvation stress, whereas poplars with knocked-down GRF1 exhibit opposite phenotypes. These results suggest that GRF1 positively influences these biological processes. Further analysis reveals that GRF1 interacts with GIF2 to up-regulate expression level of the auxin biosynthesis gene TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS 1, thereby promoting auxin content which in turn leads to modifications in root architecture under Pi deficiency for more Pi uptake. Our findings underscore the pivotal role of GRF1 in mediating root development under Pi starvation, provide novel insights into the molecular pathways involved in the Pi starvation response in woody species such as poplar, and offer potential targets for genetic engineering aimed at improving plant resilience to low Pi environments.