Tree physiology最新文献

Sulfate-proton co-transporters (SULTRs) mediate sulfate uptake, transport, storage and assimilation in plants. The SULTR family has historically been classified into four groups (SULTR1-SULTR4), with well-characterized roles for SULTR groups 1, 2 and 4. However, the functions of the large and diverse SULTR3 group remain poorly understood. Here, we present an updated phylogenetic analysis of SULTRs across angiosperms, including multiple early-divergent lineages. Our results suggest that the enigmatic SULTR3 group comprises four distinct subfamilies that predate the emergence of angiosperms, providing a basis for reclassifying the SULTR family into seven subfamilies. This expanded classification is supported by subfamily-specific gene structures and amino acid substitutions in the substrate-binding pocket. Structural modeling identified three serine residues uniquely lining the substrate-binding pocket of SULTR3.4, enabling three hydrogen bonds with the phosphate ion. The data support the proposed neofunctionalization of this subfamily for phosphate allocation within vascular tissues. Transcriptome analysis of Populus tremula × Populus alba revealed divergent tissue expression preferences among SULTR subfamilies and between genome duplicates. We observed partitioned expression in vascular tissues among the four SULTR3 subfamilies, with PtaSULTR3.4a and PtaSULTR3.2a preferentially expressed in primary and secondary xylem, respectively. Gene coexpression analysis revealed coordinated expression of PtaSULTR3.4a with genes involved in phosphate starvation responses and nutrient transport, consistent with a potential role in phosphate homeostasis. In contrast, PtaSULTR3.2a was strongly coexpressed with lignification and one-carbon metabolism genes and their upstream transcription regulators. PtaSULTR3.2a belongs to a eudicot-specific branch of the SULTR3.1 subfamily found only in perennial species, suggesting a specialized role in lignifying tissues. Together, our findings provide a refined phylogenetic framework for the SULTR family and suggest that the expanded SULTR3 subfamilies have undergone neofunctionalization during the evolution of vascular and perennial plants.

Understanding the biological mechanisms underlying tree responses to drought is critical for preserving forest biodiversity, as current global climate change is challenging the ability of drought-sensitive trees to cope with water shortage. In this study, we investigate how silver fir (Abies alba Mill.) responds to experimental drought stress, more specifically, atmospheric drought caused by high vapor pressure deficit (VPD), by analyzing the gene expression and DNA methylation profiles of different organs alongside physiological variables under well-watered, drought and recovery conditions. Roots exhibited a stronger transcriptomic response than leaves, with 50 times more altered transcripts, revealing their value for assessing water stress in this species through the expression of genes involved in water transport. In addition, brassinosteroid-related genes can serve as stress markers both in roots and leaves. VPD-induced drought also affected DNA methylation, which, like transcriptomic and physiological variables, begins to normalize once the stress is over, suggesting some resilience to drought. However, A. alba struggles to improve intrinsic water-use efficiency, which raises its vulnerability to VPD-induced drought. Our results suggest that silver fir forests might be able to cope with short drought events, but prolonged periods of water shortage, which are likely to increase with climate change, may surpass their resilience thresholds, increasing the likelihood of hydraulic failure and carbon starvation.

Members of the salicaceous genus Populus are primarily used by plant biologists as a model system for understanding the genetic underpinnings of woody plant growth and development. Beyond their importance to those conducting developmental research, Populus spp. are key members of ecosystems in the Northern Hemisphere and show promise as a vital renewable source of biomass for sustainable biofuel production. This genus also produces a class of signature herbivore-deterring and medicinally significant phenolic glycosides, commonly referred to as salicinoids. Although salicinoids in Populus are primarily associated with defense against biotic disturbances, they have also been implicated in structuring the chemotaxonomy of Populus and Salicaceae, shaping endophytic microbiomes, directing abiotic stress responses and participating in primary metabolism. Despite advancements in understanding these interactions through functional genomics and biotechnological techniques such as CRISPR/Cas9, much about their function and biosynthesis still remains obfuscated. Here, we summarize a global view of progress made in Populus salicinoid research, focusing particularly on studies conducted through a biotechnological lens, to elucidate the distribution, ecological significance, and biosynthesis of these compounds.

Wood fiber has been extensively used in the pulp and papermaking industries. The length of fiber cells is critical in determining the quality of paper. In our previous studies, we identified PdCel9A6, a gene encoding endo-1,4-β-glucanases expressed in the developing xylem to affect cell wall formation. In this study, we modified the PdCel9A6 expression specifically in xylem fiber cells. The results showed that the fiber-specific upregulation of PdCel9A6 resulted in increased plant height and internode length. The transgenics significantly increased the fiber cell length in the wood xylem. In wood cell wall components, the transgenics showed a reduction of lignin while increasing cellulose. Furthermore, the characteristics of the paper processed from the transgenics showed a significant improvement in paper strength. Transcriptome studies showed that upregulation of PdCel9A6 in fiber cells leads to changes in transcription related to cell wall remodeling and thickening during xylem development. Together, the study demonstrated a new strategy of fiber cell wall modification that could have the potential to improve forest trees for better pulping and papermaking.

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.