A Comparative Analysis of Transcription Networks Active in Juvenile and Mature Wood in Populus

Abstract

Background: Juvenile wood (JW) and mature wood (MW) have distinct physical and chemical characters, reflecting the different wood formation over the tree life-span. However, the regulatory mechanisms that distinguish or modulate the characteristics of JW and MW in relation to each other have not been mapped. Using RNA sequencing (RNA-seq) and whole genome bisulfite sequencing (WGBS), we analyzed wood properties associated with JW and MW forming tissue from Populus trees with an identical genetic background.Results: JW and MW of Populus displayed different wood properties as the result of significant differences in transcriptional programs and patterns of DNA methylation. Differences were concentrated in gene networks involved in regulating hormonal signaling pathways responsible for auxin distribution and brassinosteroids biosynthesis as well as genes active in regulating cell expansion and secondary cell wall biosynthesis. An observed correlation between gene expression profiling and DNA methylation indicated that DNA methylation affected expression of the genes related to auxin distribution and brassinosteroids signal transduction, cell expansion in JW and MW formation. Conclusions: Auxin distribution, brassinosteroids biosynthesis and signaling play critical roles in formation of JW and MW. DNA methylation is involved in formatting the transcriptional programs in different development phases which contribute to JW and MW formation. The study sheds light to better understand the molecular networks underlying regulation of wood properties which could inform improvement of wood formation.

Mechanical characterisation of the developing cell wall layers of tension wood fibres by Atomic Force Microscopy

“…The values of the indentation modulus in the different layers and the embedding resin are consistent with the (rather scattered) AFM data or nanoindentation measurements of wood cell walls available in the literature (Eder et al ., 2013), although in the low range compared literature data on the G-layer of poplar or tension wood (see Table 1). These low values can probably be partly explained by the fact that the tree used in our study was young (less than 3-month old), and the juvenile wood it produced had a high microfibril angle (MFA) in the S 2 -layer and low cellulose content (Luo et al ., 2021), and the fact that the cell used as an example in Fig. 2 was not fully mature.…”

“…These low values can be partly explained by the young age of the tree used in our study (less than 3-month old). Indeed, the juvenile wood is known for its high microfibril angle (MFA) in the S2-layer and its low cellulose content (Luo et al ., 2021). The values of the indentation modulus in the G-layer of a mature cell increased to around 18.3±3.1 GPa on average (see Fig.…”

“…These low values can be partly explained by the young age of the tree used in our study (less than 3-month old). Indeed, the juvenile wood is known for its high microfibril angle (MFA) in the S2-layer and its low cellulose content (Luo et al, 2021).…”