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

Ilka N Abreu,Björn Sundberg,Thomas Moritz,Katarzyna Sokołowska,Annika I Johansson,Nathaniel R Street,Totte Niittylä,Torgeir R Hvidsten

doi:10.1111/nph.16799

Abstract

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.

Highlights

With a growing demand for sustainable products, wood is becoming an increasingly important source of renewable biomass
Untargeted metabolomics data order wood samples according to the developmental gradient Principal component analysis (PCA) score plots of the untargeted metabolomics data from the cryosections highlighted the complementary value of the two different techniques (GC-mass spectra (MS) and LCMS): The Gas chromatography–mass spectrometry (GC-MS) profiling displays phloem and cambium samples as one cluster and expanding and mature xylem as a distinctly different second cluster (Fig. S4a)
The Liquid chromatography–mass spectrometry (LC-MS) profiling, on the other hand, shows an ordered sample distribution from phloem, through cambium and expanding xylem, to mature xylem, suggesting clear metabolite gradients coinciding with the developmental gradient of these tissues (Fig. 1a) and revealing a more complex and differentiated composition of specialized metabolites in contrast to the primary metabolites detected by GC-MS

Summary

Introduction

With a growing demand for sustainable products, wood is becoming an increasingly important source of renewable biomass. There have been very few studies profiling differences in metabolite concentrations between different cell types in the wood forming zone of angiosperm trees (Uggla et al, 2001; Andersson-Gunneras et al, 2006; Immanen et al, 2016; Ning et al, 2018). Plant hormones are important as regulators of cambial activity and differentiation. There is evidence that auxin (indole 3-acetic acid; IAA) is a key organizer of cambial growth and vascular development; for example, there is a gradient of IAA concentration across the developing cambium, suggesting that this compound plays a role in positional signaling (Uggla et al, 1996). There are data suggesting that interactions between IAA and gibberellins (GAs) can play a part in

Methods

Results

Conclusion