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Metabolomic analyses of wood attributes in tree species Robinson, Andrew Raymond

Abstract

Metabolomics is an emerging field in functional plant biology that attempts to relate patterns in the molecular intermediates and products of metabolic pathways with genetic, gene expression, environmental and phenotypic traits - at the whole-tissue and/or whole-organism level. There is enormous potential for metabolomics tools to be applied in the study of tree species, and the demand for widespread application is promoting an ongoing evolution and refinement of newly-developed techniques. This body of research addresses the application of broad-scale, non-targeted metabolomics to questions of wood formation and quality in tree systems. Overall, it was shown that variation in metabolite profiles from developing xylem tissue was indeed correlated with the strength of specific phenotypic traits. Frequently, the strength of these relationships was such that phenotypic severity could be predicted accurately on the basis of metabolite profile data alone. The specific correlative patterns and metabolite/trait pairings observed in each study provided insight into the biological mechanisms by which these traits arise. Studies of secondary xylem development were conducted on breeding populations of Douglas-fir and radiata pine, as well as genetically modified hybrid poplar. In the Douglas-fir families studied, environment-induced variation in growth rate, fibre morphology and wood chemistry were correlated with metabolite profiles from developing xylem; metabolites involved in carbohydrate and lignin biosynthesis were primarily implicated in these relationships. Similarly, in juvenile trees from a series of radiata pine families, correlations were observed between metabolite profiles of developing xylem and the internal checking wood defect, a known heritable trait. In a different approach, two poplar hybrids, each modified separately with two exogenous gene constructs related to lignin biosynthesis, provided controlled model systems in which to investigate the interaction between genotype, metabolite profiles of developing xylem, and physico-chemical wood traits. Wood traits and metabolite profiles alike were altered by the genetic modifications, and it was found that the metabolic impact of the transgenes was not confined to pathways that were directly coupled to lignin biosynthesis. In fact, the scarcity of lignin-related metabolites in profiles from either the wild-type or modified genotypes suggested that metabolite channelling phenomena operate in the lignin biosynthetic pathway. Moreover, the analyses demonstrated that transgene-induced gradients in phenotypic traits could be associated with similar gradients within broad-scale metabolite profiles, and also that the wood-forming metabolisms of different poplar hybrids can respond similarly to the influences of genetic manipulation, at a global level. To conclude, the demonstrated associations between genotype, the metabolism of wood formation, and wood phenotype, as revealed by metabolite profiles, confirm the value of non-targeted metabolomics as a systems biology approach to understanding and modeling growth and secondary cell wall biosynthesis in trees.

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