Project description:Wood, or secondary xylem, is the product of xylogenesis, a developmental process that begins with the proliferation of cambial derivatives and ends with mature xylem fibers and vessels with lignified secondary cell walls. Fully mature xylem has undergone a series of cellular processes, including cell division, cell expansion, secondary wall formation, lignification and programmed cell death. A complex network of interactions between transcriptional regulators and signal transduction pathways controls wood formation. However, the role of metabolites during this developmental process has not been comprehensively characterized. To evaluate the role of metabolites during wood formation, we performed a high spatial resolution metabolomics study of the wood-forming zone of Populus tremula, including laser dissected aspen ray and fiber cells. We show that metabolites show specific patterns within the wood-forming zone, following the differentiation process from cell division to cell death. The data from profiled laser dissected aspen ray and fiber cells suggests that these two cell types host distinctly different metabolic processes. Furthermore, by integrating previously published transcriptomic and proteomic profiles generated from the same trees, we provide an integrative picture of molecular processes, for example, deamination of phenylalanine during lignification is of critical importance for nitrogen metabolism during wood formation. GC-MS assay of Wood ring and extraxylary tissue is reported in the current study MTBLS1796.UPLC-MS assay of Wood ring and extraxylary tissue is reported in <a href='https://www.ebi.ac.uk/metabolights/MTBLS1797' rel='noopener noreferrer' target='_blank'>MTBLS1797</a>.UPLC-MS assay of Wood fibre and ray cell tissue is reported in <a href='https://www.ebi.ac.uk/metabolights/MTBLS1831' rel='noopener noreferrer' target='_blank'>MTBLS1831</a>.

Project description:Wood, or secondary xylem, is the product of xylogenesis, a developmental process that begins with the proliferation of cambial derivatives and ends with mature xylem fibers and vessels with lignified secondary cell walls. Fully mature xylem has undergone a series of cellular processes, including cell division, cell expansion, secondary wall formation, lignification and programmed cell death. A complex network of interactions between transcriptional regulators and signal transduction pathways controls wood formation. However, the role of metabolites during this developmental process has not been comprehensively characterized. To evaluate the role of metabolites during wood formation, we performed a high spatial resolution metabolomics study of the wood-forming zone of Populus tremula, including laser dissected aspen ray and fiber cells. We show that metabolites show specific patterns within the wood-forming zone, following the differentiation process from cell division to cell death. The data from profiled laser dissected aspen ray and fiber cells suggests that these two cell types host distinctly different metabolic processes. Furthermore, by integrating previously published transcriptomic and proteomic profiles generated from the same trees, we provide an integrative picture of molecular processes, for example, deamination of phenylalanine during lignification is of critical importance for nitrogen metabolism during wood formation. UPLC-MS assay of Wood ring and extraxylary tissue is reported in the current study MTBLS1797.GC-MS assay of Wood ring and extraxylary tissue is reported in <a href='https://www.ebi.ac.uk/metabolights/MTBLS1796' rel='noopener noreferrer' target='_blank'>MTBLS1796</a>.UPLC-MS assay of Wood fibre and ray cell tissue is reported in <a href='https://www.ebi.ac.uk/metabolights/MTBLS1831' rel='noopener noreferrer' target='_blank'>MTBLS1831</a>.

Project description:Woody plant material represents a vast renewable resource that has the potential to produce biofuels and other bio-based products with favourable net CO2 emissions1,2. Its potential has been demonstrated in a recent study that generated novel structural materials from flexible mouldable wood3. The study of viral infection in plants has largely focussed on detrimental symptoms, such as leaf yellowing or cell death that result in reduced crop yields. Apple rubbery wood (ARW) disease is the result of a viral infection that causes woody stems to exhibit increased flexibility4. While ARW disease is associated with the presence of an RNA virus5 (ARWV), the mechanism underlying the development of its unique symptoms is not known. We demonstrate that ARWV symptoms arise from reduced lignification within the secondary cell wall of xylem fibres, while the mid-lamellae region and xylem ray cells are largely unaffected, and results in increased wood digestibility. Gene expression and proteomic data from symptomatic xylem clearly show the downregulation of phenylalanine ammonia lyase (PAL), the enzyme catalysing the first committed step in the phenylpropanoid pathway leading 2 to lignin biosynthesis. PAL downregulation is the likely cause of the decreased lignification, which is consistent with a large increase in soluble phenolics, including the lignin precursor phenylalanine, seen in symptomatic xylem. ARWV-infection results in the accumulation of many host-derived viral activated small interfering RNAs (vasiRNAs). PAL-derived vasiRNAs are among the most abundant vasiRNAs in symptomatic xylem and are likely the cause of reduced PAL activity. Apparently, the mechanism used by the virus to alter lignin exhibits similarities to the RNAi strategy that has been used to alter lignin in genetically modified trees to generate comparable improvements in wood properties6–8. CRISPR technology was recently used to increase yields in maize by introducing the naturally occurring waxy mutation into maize9. A similar biomimetic approach for biomass improvement based upon our understanding of ARWV symptoms offers a promising route to improve wood properties and provides important context for the genetic manipulation of trees.

Project description:The within-tree variation in wood properties constitutes an exceptional model to study the mechanisms that adjust the different biosynthetic pathways providing substrates with the massive and variable demands of different biosynthetic reactions of cell wall polymers. Although a few genes have been reported as differentially expressed in differentiating compression wood compared to normal or opposite wood, the expression of a larger set of genes is expected to change due the broad range of features that distinguish this reaction wood. By combining the construction of different cDNA libraries with microarray analyses, using samples from different Pinus pinaster provenances collected in different years and geographic locations, we have identified a total of 496 genes that change their expression during differentiation of compression wood (331 up-regulated and 165 down-regulated compared to opposite wood). Consistent with the well-known structural and chemical characteristics of compression wood, a large number of genes involved in the biosynthesis of cell wall components were shown to be up-regulated during compression wood differentiation, including genes involved in synthesis of cellulose, hemicellulose, lignin and lignans. In particular, further analysis of a set of these genes involved in providing S-adenosylmethionine, ammonium recycling, lignin and lignans biosynthesis showed parallel expression profiles to levels of lignin accumulation in cells undergoing xylogenesis in vivo and in vitro. The comparative transcriptomic analysis of compression and opposite wood formation in this work have revealed a broad spectrum of coordinated transcriptional modulation of biosynthetic reactions for different cell wall polymers associated to within-tree variations in softwood structure and composition. In particular, it suggest the occurrence of a mechanism that modulates at transcriptional level genes encoding enzymes involved in S-adenosylmethionine synthesis and ammonium assimilation with coniferyl alcohol demand for lignin and lignan synthesis, as a key metabolic requirement in cells undergoing lignification. Two-condition experiment including dye-swap experiments, Compression Differentiating Xylem vs. Opposite Differentiating Xylem. Biological replicates: 4 compression xylem, 4 opposite xylew, harvested from four different individual pine trees. Two replicates per array.

Dataset Information

A metabolite roadmap of the wood-forming tissue in Populus tremula (UPLC-MS assay; Wood fibre and ray cell tissue)

Publications

A metabolite roadmap of the wood-forming tissue in Populus tremula.

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