Assessing the between-background stability of metabolic effects arising from lignin-related transgenic modifications, in two Populus hybrids using non-targeted metabolomics.

The advances in 'high-throughput' biology have significantly expanded our fundamental understanding of complex biological processes inherent to tree growth and development. Relative to the significant achievements attained with whole genome re-sequencing and transcriptomics efforts, the development and power of post-transcriptional tools such as proteomics and metabolomics continue to lag behind in tree biology. However, the inclusion of these powerful functional genomics platforms should substantially enable systems biology assessments of tree development, physiology and response(s) to biotic and abiotic stresses. Herein, we employ a non-targeted metabolomics platform to elucidate the metabolic plasticity of xylem lignification in distinct hybrid poplar genetic backgrounds, as well as in transgenic trees in these backgrounds expressing two common constructs: the first construct (C4H::F5H) augments monolignol content (syringyl:guaiacyl (S:G) ratio), while the second construct (C3'H-RNAi) reduces cell wall lignification. The results clearly show that genotype-specific metabolism exists, and provide an appropriate foundation for properly comparing the influence of background on the relationships between metabolic and specific phenotypic traits. Moreover, it was apparent that transgene-induced phenotypic gradients in cell wall chemical wood can be associated with global metabolism of secondary xylem biosynthesis, however in a genotype-specific manner. This result implies that the same may be true for phenotypic gradients arising through natural genetic variation, intensive breeding or environmental factors. It is also apparent that while distinct, at a global level the wood-forming metabolisms of different poplar hybrids can, to some extent, respond similarly to the influences of genetic manipulation of lignin-related genes. This further implies that with the correct approach, it may be possible to associate the emergence of specific wood traits from different genetic backgrounds-be they transgene-induced or otherwise-with stable metabolic signatures.